Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	FGEN
Entity Registrant Name	FIBROGEN INC
Entity Central Index Key	0000921299
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		82,666,979
Entity Public Float			$ 1,674.4

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 673,658	$ 173,782
Short-term investments	62,060	79,397
Accounts receivable ($4,004 and $4,102 from a related party)	8,452	10,448
Prepaid expenses and other current assets	4,800	2,889
Total current assets	748,970	266,516
Restricted time deposits	5,181	6,217
Long-term investments	10,506	71,010
Property and equipment, net	129,476	123,657
Other assets	4,517	2,152
Total assets	898,650	469,552
Current liabilities:
Accounts payable	5,509	6,223
Accrued liabilities ($272 and $1,615 to a related party)	63,781	50,914
Deferred revenue	7,968	7,988
Total current liabilities	77,258	65,125
Long-term portion of lease financing obligations	97,763	97,352
Product development obligations	17,244	14,854
Deferred rent	3,657	4,212
Deferred revenue, net of current	112,231	106,709
Other long-term liabilities	8,047	6,191
Total liabilities	316,200	294,443
Commitments and Contingencies (Note 8)
Stockholders’ equity:
Preferred stock, $0.01 par value; 125,000 shares authorized at December 31, 2017 and December 31, 2016; no shares issued and outstanding at December 31, 2017 and December 31, 2016	0	0
Common stock, $0.01 par value; 225,000 shares authorized at December 31, 2017 and December 31, 2016; 82,498 and 63,665 shares issued and outstanding at December 31, 2017 and December 31, 2016	825	637
Additional paid-in capital	1,160,094	625,903
Accumulated other comprehensive loss	(1,795)	(960)
Accumulated deficit	(595,945)	(469,742)
Total stockholders’ equity	563,179	155,838
Non-controlling interests	19,271	19,271
Total equity	582,450	175,109
Total liabilities, stockholders’ equity and non-controlling interests	$ 898,650	$ 469,552

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Accounts receivable from related party	$ 4,004	$ 4,102
Accrued liabilities to related party	$ 272	$ 1,615
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	125,000,000	125,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	225,000,000	225,000,000
Common stock, shares issued	82,498,000	63,665,000
Common stock, shares outstanding	82,498,000	63,665,000

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
License and milestone revenue (includes $15,307, $24,421 and $18,701 from a related party)	$ 96,056	$ 137,352	$ 148,093
Collaboration services and other revenue (includes $1,578, $1,357 and $2,895 from a related party)	29,612	42,225	32,735
Total revenue	125,668	179,577	180,828
Operating expenses:
Research and development	196,517	187,206	214,089
General and administrative	51,760	46,025	44,364
Total operating expenses	248,277	233,231	258,453
Loss from operations	(122,609)	(53,654)	(77,625)
Interest and other, net
Interest expense	(9,706)	(10,725)	(11,033)
Interest income and other, net	6,433	2,628	3,121
Total interest and other, net	(3,273)	(8,097)	(7,912)
Loss before income taxes	(125,882)	(61,751)	(85,537)
Provision for (benefit from) income taxes	321	(71)	242
Net loss	$ (126,203)	$ (61,680)	$ (85,779)
Net loss per share - basic and diluted	$ (1.73)	$ (0.98)	$ (1.42)
Weighted average number of common shares used to calculate net loss per share - basic and diluted	72,987	62,744	60,337

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
License and milestone revenue from a related party	$ 96,056	$ 137,352	$ 148,093
Collaboration services and other revenue from a related party	29,612	42,225	32,735
Astellas Agreement [Member]
License and milestone revenue from a related party	15,307	24,421	18,701
Collaboration services and other revenue from a related party	$ 1,578	$ 1,357	$ 2,895

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (126,203)	$ (61,680)	$ (85,779)
Other comprehensive income (loss):
Foreign currency translation adjustments	(2,022)	532	1,662
Available-for-sale investments:
Unrealized gain on investments, net of tax effect	1,259	140	30
Reclassification from accumulated other comprehensive loss	(72)	19	(194)
Net change in unrealized gain on available-for-sale investments	1,187	159	(164)
Other comprehensive income (loss), net of taxes	(835)	691	1,498
Comprehensive loss	$ (127,038)	$ (60,989)	$ (84,281)

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Noncontrolling Interests [Member]
Balance at Dec. 31, 2014	$ 240,676	$ 590	$ 546,247	$ (3,149)	$ (322,283)	$ 19,271
Balance, Shares at Dec. 31, 2014		59,046,296
Net loss	(85,779)	$ 0	0	0	(85,779)	0
Change in unrealized loss on investments	(164)	0	0	(164)	0	0
Foreign currency translation adjustments	1,662	0	0	1,662	0	0
Shares issued from stock plans, net of payroll taxes paid	12,707	$ 29	12,678	0	0	0
Shares issued from stock plans, net of payroll taxes paid, Shares		2,817,988
True up of issuance costs related to initial public offering and common stock sold by FibroGen Europe	42	$ 0	42	0	0	0
Stock-based compensation	27,681	0	27,681	0	0	0
Warrants exercised	0	$ 1	(1)	0	0	0
Warrants exercised, Shares		120,795
Balance at Dec. 31, 2015	196,825	$ 620	586,647	(1,651)	(408,062)	19,271
Balance, Shares at Dec. 31, 2015		61,985,079
Net loss	(61,680)	$ 0	0	0	(61,680)	0
Change in unrealized loss on investments	159	0	0	159	0	0
Foreign currency translation adjustments	532	0	0	532	0	0
Shares issued from stock plans, net of payroll taxes paid	7,141	$ 17	7,124	0	0	0
Shares issued from stock plans, net of payroll taxes paid, Shares		1,660,759
Stock appreciation rights settled	0	$ 0	0	0	0	0
Stock appreciation rights settled, Shares		17,855
Stock-based compensation	32,132	$ 0	32,132	0	0	0
Warrants exercised	0	$ 0	0	0	0	0
Warrants exercised, Shares		1,591
Balance at Dec. 31, 2016	175,109	$ 637	625,903	(960)	(469,742)	19,271
Balance, Shares at Dec. 31, 2016		63,665,284
Net loss	(126,203)	$ 0	0	0	(126,203)	0
Change in unrealized loss on investments	1,187	0	0	1,187	0	0
Foreign currency translation adjustments	(2,022)	0	0	(2,022)	0	0
Follow-on Offerings, net of underwriting discounts, commission and issuance costs	470,226	$ 144	470,082	0	0	0
Follow-on Offerings, net of underwriting discounts, commission and issuance costs, Shares		14,428,750
Shares issued from stock plans, net of payroll taxes paid	26,614	$ 44	26,570	0	0	0
Shares issued from stock plans, net of payroll taxes paid, Shares		4,404,094
Stock-based compensation	37,539	$ 0	37,539	0	0	0
Balance at Dec. 31, 2017	$ 582,450	$ 825	$ 1,160,094	$ (1,795)	$ (595,945)	$ 19,271
Balance, Shares at Dec. 31, 2017		82,498,128

Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (126,203)	$ (61,680)	$ (85,779)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	6,099	6,040	5,679
Amortization of premium on investments	1,844	2,729	2,997
Unrealized loss (gain) on short-term investments	2	0	0
Gain on disposal of property and equipment	3	0	98
Stock-based compensation	37,539	32,132	27,681
Tax benefit on unrealized gain on available-for-sale securities	0	(211)	0
Realized gain on sales of available-for-sale securities	(143)	(37)	(203)
Changes in operating assets and liabilities:
Accounts receivable ($98, $353 and $578 from related party)	1,996	4,957	(1,952)
Prepaid expenses and other current assets	(1,911)	1,099	978
Other assets	(2,365)	(136)	(420)
Accounts payable	(714)	(298)	1,970
Accrued liabilities ($(1,343), $(430) and $(2,549) from related party)	9,196	2,965	(2,126)
Deferred revenue	5,502	16,837	27,654
Lease financing liability	1,023	814	627
Other long-term liabilities	1,619	1,897	4,225
Net cash provided by (used in) operating activities	(66,513)	7,108	(18,571)
Investing activities
Purchases of property and equipment	(8,500)	(1,252)	(1,977)
Proceeds from sale of property and equipment	5	0	2
Purchases of available-for-sale securities	(169)	(9,041)	(41,736)
Proceeds from sales of available-for-sale securities	21,109	4,298	15,342
Proceeds from maturities of available-for-sale securities	57,421	12,617	22,501
Net cash provided by (used in) investing activities	69,866	6,622	(5,868)
Financing activities
Repayments of lease liability	(403)	(403)	(403)
Proceeds from follow-on offerings, net of underwriting discounts and commission costs	471,205	0	0
Cash paid for payroll taxes on restricted stock unit releases	(8,296)	(2,740)	(2,243)
Proceeds from issuance of common stock	34,910	9,881	14,992
Payments of deferred offering costs	(944)	0	0
Net cash provided by financing activities	496,472	6,738	12,346
Effect of exchange rate change on cash and cash equivalents	51	(10)	(38)
Net increase (decrease) in cash and cash equivalents	499,876	20,458	(12,131)
Total cash and cash equivalents at beginning of period	173,782	153,324	165,455
Total cash and cash equivalents at end of period	673,658	173,782	153,324
Supplemental cash flow information:
Interest payments	255	295	335
Balance in accounts payable and accrued liabilities related to purchases of property and equipment	3,781	356	931
Deferred offering costs recorded in accounts payable and accrued liabilities	$ 35	$ 0	$ 0

Consolidated Statement of Cash Flows (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Cash Flows [Abstract]
Accounts receivable from related party	$ 98	$ 353	$ 578
Accrued liabilities from related party	$ (1,343)	$ (430)	$ (2,549)

The Company

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

The Company

1.	The Company

FibroGen, Inc. (“FibroGen” or the “Company”) was incorporated in 1993 in Delaware and is a research-based biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutics agents to treat serious unmet medical needs. The Company’s focus in the areas of fibrosis and hypoxia-inducible factor (“HIF”) biology has generated multiple programs targeting various therapeutic areas. The Company’s most advanced product candidate, roxadustat, or FG-4592, is an oral small molecule inhibitor of HIF prolyl hydroxylases (“HIF-PHs”) in Phase 3 clinical development for the treatment of anemia in chronic kidney disease (“CKD”). Pamrevlumab, or FG-3019, is the Company’s monoclonal antibody in Phase 2 clinical development for the treatment of idiopathic pulmonary fibrosis (“IPF”), pancreatic cancer, Duchenne muscular dystrophy (“DMD”) and liver fibrosis. The Company has taken a global approach with respect to the development and future commercialization of its product candidates, and this includes development and commercialization in the People’s Republic of China (“China”). The Company is capitalizing on its extensive experience in fibrosis and HIF biology and clinical development to advance a pipeline of innovative medicines for the treatment of anemia, fibrotic disease cancer, corneal blindness and other serious unmet medical needs.

On April 11, 2017, the Company closed a follow-on offering of its common stock. In this offering, the Company sold 5,228,750 shares of its common stock at a public offering price of $22.95 per share. Net proceeds from this offering were $115.1 million, after deducting underwriting discounts and commissions of $4.9 million. In addition, the offering expenses were approximately $0.6 million in total. On August 24, 2017, the Company completed another follow-on offering of its common stock. In this offering, the Company sold a total of 9,200,000 shares of its common stock at a public offering price of $40.75 per share. Net proceeds from this offering were $356.2 million, after deducting underwriting discounts and commissions of $18.7 million. In addition, the offering expenses were approximately $0.4 million in total.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

Basis of Presentation

The consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The consolidated financial statements include the accounts of the Company, its wholly owned subsidiaries and its majority-owned subsidiaries, FibroGen Europe and FibroGen China Anemia Holdings, Ltd. (“FibroGen China”). All inter-company transactions and balances have been eliminated in consolidation.

The Company operates in one segment — the discovery, development and commercialization of novel therapeutics to treat serious unmet medical needs.

Based upon the current status of, and plans for, its product development, the Company believes that its existing cash and cash equivalents and its short term and long term investments, in addition to expected milestone payments related to certain collaboration agreements, will be adequate to satisfy the Company’s capital needs through at least the next 12 months from the issuance of the consolidated financial statements. However, the process of developing and commercializing products requires significant research and development, preclinical testing and clinical trials, manufacturing arrangements as well as regulatory approvals. These costs, together with the Company’s general and administrative expenses, are expected to result in operating losses until the commercialization of the Company’s products or partner collaborations generate sufficient revenue to cover expenses. To achieve sustained profitability, the Company, alone or with others, must successfully develop its product candidates, obtain required regulatory approvals and successfully manufacture and market its products.

Foreign Currency Translation

The reporting currency of the Company and its subsidiaries is the United States (“U.S.”) dollar. The functional currency of FibroGen Europe is the Euro. The assets and liabilities of FibroGen Europe are translated to U.S. dollars at exchange rates in effect at the balance sheet date. All income statement accounts are translated at monthly average exchange rates. Resulting foreign currency translation adjustments are recorded directly in accumulated other comprehensive income (loss) as a separate component of stockholders’ equity.

The functional currency of FibroGen, Inc. and all other subsidiaries is the U.S. dollar. Accordingly, monetary assets and liabilities in the non-functional currency of these subsidiaries are remeasured using exchange rates in effect at the end of the period. Revenues and costs in local currency are remeasured using average exchange rates for the period, except for costs related to those balance sheet items that are remeasured using historical exchange rates. The resulting remeasurement gains and losses are included within interest income and other, net in the consolidated statements of operations as incurred and have not been material for all periods presented.

Use of Estimates

The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. The more significant areas requiring the use of management estimates and assumptions include valuation and recognition of revenue, estimates of accruals related to clinical trial costs, valuation allowances for deferred tax assets, and valuation and recognition of stock-based compensation. On an ongoing basis, management reviews these estimates and assumptions. Changes in facts and circumstances may alter such estimates and actual results could differ from those estimates.

Concentration of Credit Risk and Other Risks and Uncertainties

The Company is subject to risks associated with concentration of credit for cash and cash equivalents. A portion of cash on hand is invested in a diversified portfolio of investment grade corporate bonds issued by U.S. corporations as rated investment grade corporate bonds. Any remaining cash is deposited with major financial institutions in the U.S., Finland, China and the Cayman Islands. At times, such deposits may be in excess of insured limits. The Company has not experienced any loss on its deposits of cash and cash equivalents. Included in current assets are significant balances of accounts receivable as follows:

	December 31,
	2017			2016
Astellas Pharma Inc. (“Astellas”)—Related party		47	%		39	%
AstraZeneca AB (“AstraZeneca”)		53	%		61	%

The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, rapid technological change, the results of clinical trials and the achievement of milestones, market acceptance of the Company’s product candidates, competition from other products and larger companies, protection of proprietary technology, strategic relationships and dependence on key individuals.

Cash, Cash Equivalents and Restricted Time Deposits

The Company considers all highly liquid investments with maturities of three months or less and that are used in the Company’s cash management activities at the date of purchase to be cash equivalents. Cash and cash equivalents include money market accounts, various deposit accounts, and money market funds. Restricted time deposits include an irrevocable standby letter of credit as security deposit for a long-term property lease with the Company’s landlord. Restricted time deposits as of December 31, 2017 and 2016 totaled $5.2 million and $6.2 million, respectively. As of December 31, 2017, a total of $32.3 million of the Company’s cash and cash equivalents is held outside of the U.S. in the Company’s foreign subsidiaries to be used primarily for the Company’s China operations.

Investments

The Company classifies its investments as available-for-sale. Those investments with maturities less than 12 months are considered short-term investments. Those investments with maturities greater than 12 months are considered long-term investments. The Company’s investments classified as available-for-sale are recorded at fair value based upon quoted market prices at period end. Unrealized gains and losses that are deemed temporary in nature are recorded in accumulated other comprehensive income (loss) as a separate component of stockholders’ equity.

A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. Premiums and discounts are amortized (accreted) over the life of the related security as an adjustment to its yield. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of investments sold.

Fair Value of Financial Instruments

Carrying amounts of certain of the Company’s financial instruments including cash equivalents, investments, receivables, accounts payable and accrued liabilities approximate fair value (refer to Note 4).

Property and Equipment

Property and equipment (except for costs of construction of certain long-lived assets — refer to Note 8) are recorded at cost and depreciated over their estimated useful lives using the straight-line method. Computer equipment, laboratory equipment, and furniture and fixtures are depreciated over three to five years. Leasehold improvements are recorded at cost and amortized over the term of the lease or their useful life, whichever is shorter.

Impairment of Long-Lived Assets

The Company continually evaluates whether events or circumstances have occurred that indicate that the estimated remaining useful life of its long-lived assets may warrant revision or that the carrying value of these assets may be impaired. If the Company determines that an impairment trigger has been met, the Company evaluates the realizability of its long-lived assets based on a comparison of projected undiscounted cash flows from use and eventual disposition with the carrying value of the related asset. Any write-downs (which are measured based on the difference between the fair value and the carrying value of the asset) are treated as permanent reductions in the carrying amount of the assets (asset group). Based on this evaluation, the Company believes that, as of each of the balance sheet dates presented, none of the Company’s long-lived assets were impaired.

Revenue Recognition

Substantially all of the Company’s revenues to date have been generated from its collaboration agreements.

The Company’s collaboration agreements include multiple deliverables, and the Company therefore follows the guidance in Accounting Standards Codification (“ASC”) Topic 605-25, Revenue Recognition—Multiple-Element Arrangements, (“ASC 605-25”), which:

•	provides guidance on how deliverables in an arrangement should be separated and how the arrangement consideration should be allocated to the separate units of accounting;

•	requires an entity to determine the selling price of a separate deliverable using a hierarchy of (i) vendor-specific objective evidence (“VSOE”), (ii) third-party evidence (“TPE”), or (iii) best estimate of selling price (“BESP”); and

•	requires the allocation of the arrangement consideration, at the inception of the arrangement, to the separate units of accounting based on relative selling price.

The Company evaluates all deliverables within an arrangement to determine whether or not they provide value on a stand-alone basis. Based on this evaluation, the deliverables are separated into units of accounting. The arrangement consideration that is fixed or determinable at the inception of the arrangement is allocated to the separate units of accounting based on their relative selling prices. Significant judgment may be required in determining whether a deliverable provides stand-alone value, determining the amount of arrangement consideration that is fixed or determinable, and estimating the stand-alone selling price of each unit of accounting.

To date, the Company has determined that the selling price for the deliverables within its collaboration agreements should be determined using BESP, as neither VSOE nor TPE is available. The process for determining BESP involves significant judgment on the Company’s part and includes consideration of multiple factors, including assumptions related to the market opportunity and the time needed to commercialize a product candidate pursuant to the relevant license, estimated direct expenses and other costs, which include the rates normally charged by contract research and contract manufacturing organizations for development and manufacturing obligations, and rates that would be charged by qualified outsiders for committee services.

For each unit of accounting identified within an arrangement, the Company determines the period over which the deliverables are provided and the performance obligation is satisfied. Service revenue is recognized using a proportional performance method. Direct labor hours or full time equivalents are typically used as the measurement of performance. Revenue may be recognized using a straight line method when performance is expected to occur roughly consistently over a period of time.

Payments or reimbursements resulting from the Company’s research and development efforts for those arrangements where such efforts are considered as deliverables are recognized as the services are performed and are presented on a gross basis. To the extent payments are required to be made to the collaboration partners pursuant to research and development efforts, those costs are charged to research and development using the guidance pursuant to ASC 605-250, Customer Payments and Incentives, which states that cash consideration given by a vendor to a customer is presumed to be a reduction of the selling prices unless the vendor receives an identifiable benefit in exchange for the consideration that is sufficiently separable from the recipient’s purchase of the vendor’s products, and the vendor can reasonably estimate the fair value of the benefit.

Each of the Company’s collaboration agreements includes milestones for which the Company follows ASC 605-28, Revenue Recognition—Milestone Method (“ASC 605-28”). ASC 605-28 establishes the milestone method as an acceptable method of revenue recognition for certain contingent event-based payments under research and development arrangements. Under the milestone method, a payment that is contingent upon the achievement of a substantive milestone is recognized in its entirety in the period in which the milestone is achieved. A milestone is an event (i) that can only be achieved based in whole or in part on either the Company’s performance or on the occurrence of a specific outcome resulting from the Company’s performance, (ii) for which there is substantive uncertainty at the date the arrangement is entered into that the event will be achieved and (iii) that would result in additional payments being due to the Company. Determining whether a milestone is substantive is a matter of judgment and that assessment must be made at the inception of the arrangement. Milestones are considered substantive when the consideration earned from the achievement of the milestone is (i) commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the item delivered as a result of a specific outcome resulting from the Company’s performance to achieve the milestone, (ii) relates solely to past performance and (iii) is reasonable relative to all deliverables and payment terms in the arrangement. Payments for achieving milestones which are not considered substantive are treated as additional arrangement consideration and are allocated following the relative selling price method previously described.

Research and Development Expenses

Research and development expenses consist of independent research and development costs and the gross amount of costs associated with work performed under collaboration agreements. Research and development costs include employee-related expenses, expenses incurred under agreements with clinical research organizations (“CROs”), other clinical and preclinical costs and allocated direct and indirect overhead costs, such as facilities costs, information technology costs and other overhead. All research and development costs are expensed as incurred.

Clinical Trial Accruals

Clinical trial costs are a component of research and development expenses. The Company accrues and expenses clinical trial activities performed by third parties based upon actual work completed in accordance with agreements established with clinical research organizations and clinical sites. The Company determines the costs to be recorded based upon validation with the external service providers as to the progress or stage of completion of trials or services and the agreed-upon fee to be paid for such services.

General and Administrative Expenses

General and administrative expenses consist primarily of employee-related expenses for executive, operational, finance, legal and human resource functions. Other general and administrative expenses include facility-related costs and professional service fees, other outside services, recruiting fees and expenses associated with obtaining and maintaining patents.

Income Taxes

The Company utilizes the asset and liability method of accounting for income taxes which requires the recognition of deferred tax assets and liabilities for expected future consequences of temporary differences between the financial reporting and income tax bases of assets and liabilities using enacted tax rates. Management makes estimates, assumptions and judgments to determine the Company’s provision for income taxes and also for deferred tax assets and liabilities, and any valuation allowances recorded against the Company’s deferred tax assets. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent the Company believes that recovery is not likely, the Company must establish a valuation allowance.

The calculation of the Company’s current provision for income taxes involves the use of estimates, assumptions and judgments while taking into account current tax laws, interpretation of current tax laws and possible outcomes of future tax audits. The Company has established reserves to address potential exposures related to tax positions that could be challenged by tax authorities. Although the Company believes its estimates, assumptions and judgments to be reasonable, any changes in tax law or its interpretation of tax laws and the resolutions of potential tax audits could significantly impact the amounts provided for income taxes in the Company’s consolidated financial statements.

The calculation of the Company’s deferred tax asset balance involves the use of estimates, assumptions and judgments while taking into account estimates of the amounts and type of future taxable income. Actual future operating results and the underlying amount and type of income could differ materially from the Company’s estimates, assumptions and judgments thereby impacting the Company’s financial position and results of operations.

The Company has adopted ASC 740-10, Accounting for Uncertainty in Income Taxes, that prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of uncertain tax positions taken or expected to be taken in the Company’s income tax return, and also provides guidance on derecognition, classification, interest and penalties, accounting in interim periods, disclosure and transition.

The Company includes interest and penalties related to unrecognized tax benefits within income tax expense in the Consolidated Statements of Operations.

Stock-Based Compensation

The Company maintains equity incentive plans under which incentive and nonqualified stock options are granted to employees and non-employee consultants. Compensation expense relating to non-employee stock options has not been material for all the periods presented.

The Company measures and recognizes compensation expense for all stock options and restricted stock units (“RSUs”) granted to its employees and directors based on the estimated fair value of the award on the grant date. The Company uses the Black-Scholes valuation model to estimate the fair value of stock option awards. The fair value is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award, on a straight-line basis. The Company believes that the fair value of stock options granted to non-employees is more reliably measured than the fair value of the services received. As such, the fair value of the unvested portion of the options granted to non-employees is re-measured each period. The resulting increase in value, if any, is recognized as expense during the period the related services are rendered on a straight-line basis. The determination of the grant date fair value of options using an option pricing model is affected by the Company’s estimated Common Stock fair value and requires management to make a number of assumptions including the expected life of the option, the volatility of the underlying stock, the risk-free interest rate and expected dividends.

Comprehensive Income (Loss)

The Company is required to report all components of comprehensive income (loss), including net loss, in the consolidated financial statements in the period in which they are recognized. Comprehensive income (loss) is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources, including unrealized gains and losses on investments and foreign currency translation adjustments. Comprehensive gains (losses) have been reflected in the consolidated statements of comprehensive income (loss) for all periods presented.

Recently Issued and Adopted Accounting Guidance

In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-09, Compensation - Stock Compensation (Topic 718). This guidance identifies areas for simplification involving several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, an option to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. This guidance was effective for the annual reporting period beginning after December 15, 2016, including interim periods within that reporting period. The Company adopted this guidance as of January 1, 2017 and has elected to continue with its existing policy to estimate forfeitures expected to occur when calculating stock compensation expense. Upon adoption, the Company recorded a retrospective increase of $19.5 million in deferred tax assets for previously unrecognized excess tax benefits that existed as of December 31, 2016, and a corresponding increase of $19.5 million in the valuation allowance against these deferred tax assets, as substantially all of the Company’s U.S. and foreign deferred tax assets, net of deferred tax liabilities, are subject to a full valuation allowance. As such, the net impact from these retrospective adjustments was zero to the Company’s accumulated deficit. The adoption of this guidance had no impact to the Company’s consolidated financial statements for the year ended December 31, 2017.

Recently Issued Accounting Guidance Not Yet Adopted

In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting. This guidance provides guidance about which changes to the terms or conditions of a stock-based payment award require an entity to apply modification accounting in Topic 718. This guidance is effective for annual reporting period beginning after December 15, 2017, including interim periods, with early adoption permitted. While the Company is in the process of finalizing its assessment, it expects the impact on its consolidated financial statements to be immaterial upon the adoption of this guidance.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This guidance requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability. This guidance is effective for the annual reporting period beginning after December 15, 2019, including interim periods within that reporting period. The Company is currently evaluating the impact on its consolidated financial statements upon the adoption of this guidance.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). Under this guidance, an entity is required to recognize right-of-use assets and lease liabilities on its balance sheet and disclose key information about leasing arrangements. This guidance offers specific accounting guidance for a lessee, a lessor and sale and leaseback transactions. Lessees and lessors are required to disclose qualitative and quantitative information about leasing arrangements to enable a user of the financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. This guidance is effective for the annual reporting period beginning after December 15, 2018, including interim periods within that reporting period, and requires a modified retrospective adoption, with early adoption permitted. The Company is currently evaluating the impact on its consolidated financial statements upon the adoption of this guidance.

In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10). This guidance requires equity investments that are not accounted for under the equity method of accounting to be measured at fair value with changes recognized in net income, simplifies the impairment assessment of certain equity investments, and updates certain presentation and disclosure requirements. This guidance is effective for the annual reporting period beginning after December 15, 2017 and interim periods within those annual periods. While the Company is in the process of finalizing its assessment, it expects the impact on its consolidated financial statements to be immaterial upon the adoption of this guidance.

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which supersedes the revenue recognition requirements in Accounting Standards Codification (“ASC”) 605, Revenue Recognition. ASU 2014-09 is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. Subsequently, the FASB has issued the following standards related to ASU 2014-09: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (“ASU 2016-08”); ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing (“ASU 2016-10”); ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”); and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers (“ASU 2016-20”). The Company must adopt ASU 2016-08, ASU 2016-10, ASU 2016-12 and ASU 2016-20 with ASU 2014-09 (collectively, the “new revenue standards”). The amendments may be applied retrospectively to each prior period (full retrospective) or retrospectively with the cumulative effect recognized as of the date of initial application (modified retrospective). The Company has substantially completed its evaluation related to the adoption of ASU 2014-09, applying the five-step model of the new standard to its various revenue related arrangement. The Company has concluded that its collaboration agreements with Astellas Pharma Inc. and AstraZeneca AB are the only material contracts which will be impacted by the adoption of the new revenue standards. The Company has concluded the distinct criteria evaluated under ASC 605-25 for each performance obligation will result in a similar conclusion under the new revenue standards. With respect to milestones that were previously recognized under ASC 605-28, the milestone method is not applicable under the new revenue standards, and they are considered part of the overall arrangement consideration which will result in a deferral of revenue under the new revenue standards as part of the adoption. The Company will adopt the new revenue standards in the first quarter of 2018 and apply the full retrospective method to restate each prior reporting period presented in the consolidated financial statements. Based on the current evaluation, the Company expects to record an increase in revenue of $5.3 million and $3.6 million for the years ended December 31, 2017 and 2016, respectively, a reduction in revenue of $8.4 million for the year ended December 31, 2015, and an increase in the opening accumulative deficit of $35.2 million as of e January 1, 2015. The new revenue standard is principle based and interpretation of those principles may vary from company to company based on their unique circumstances. It is possible that interpretation, industry practice, and guidance may evolve as companies and the accounting profession work to implement this new standard. The Company is still in the process of finalizing its evaluation of the effect of the new revenue standards on the Company’s historical financial statements and disclosures. As the Company completes its evaluation of these new revenue standards, new information may arise that could change the Company's current understanding of the impact to revenues recognized and its views on the expected impact to the periods prior to adoption.

Collaboration Agreements

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Collaboration Agreements

3.	Collaboration Agreements

Astellas Agreements

Japan Agreement

In June 2005, the Company entered into a collaboration agreement with Astellas Pharma Inc. (“Astellas”) for the development and commercialization (but not manufacture) of roxadustat for the treatment of anemia in Japan (“Japan Agreement”). Under this agreement, Astellas paid license fees and other consideration totaling $40.1 million (such amounts were fully received as of February 2009). The Japan Agreement also provides for additional development and regulatory approval milestone payments up to $117.5 million, a commercial sales related milestone of $15.0 million and additional consideration based on net sales (as defined) in the low 20% range after commercial launch. A clinical milestone payment of $12.5 million was received in 2013. During the second quarter of 2016, the Company recognized $10.0 million revenue as a result of the initiation by Astellas of the first Phase 3 clinical study in Japan of roxadustat for treatment of anemia associated with chronic kidney disease in patients on dialysis. The amount was received in early July 2016. The Company evaluated the criteria under ASC 605-28 and concluded that the aforementioned milestone was substantive.

Europe Agreement

In April 2006, the Company entered into a separate collaboration agreement with Astellas for the development and commercialization of roxadustat for the treatment of anemia in Europe, the Middle East, the Commonwealth of Independent States and South Africa (“Europe Agreement”). Under the terms of the Europe Agreement, Astellas paid license fees and other upfront consideration totaling $320.0 million (such amounts were fully received as of February 2009). The Europe Agreement also provides for additional development and regulatory approval milestone payments up to $425.0 million. Clinical milestone payments of $40.0 million and $50.0 million were received in 2010 and 2012, respectively. The Company evaluated the criteria under ASC 605-28 and concluded that each of those milestones was substantive. Under the Europe Agreement, Astellas committed to fund 50% of joint development costs for Europe and North America, and all territory-specific costs. The Europe Agreement also provides for tiered payments based on net sales of product (as defined) in the low 20% range.

AstraZeneca Agreements

U.S./Rest of World Agreement

Effective July 30, 2013, the Company entered into a collaboration agreement with AstraZeneca for the development and commercialization of roxadustat for the treatment of anemia in the U.S. and all other countries in the world, other than China, not previously licensed under the Astellas Europe and Astellas Japan Agreements (“U.S./RoW Agreement”). It also excludes China, which is covered by a separate agreement with AstraZeneca described below. Under the terms of the U.S./RoW Agreement, AstraZeneca has agreed to pay upfront, non-contingent and time-based payments totaling $374.0 million, which were fully received in various amounts through June 2016. In addition, the U.S./RoW Agreement also provides for development and regulatory approval based milestone payments of up to $550.0 million, which include potential future indications which the companies choose to pursue, and commercial related milestone payments of up to $325.0 million. During the second quarter of 2015, the Company received a $15.0 million development milestone payment as a result of the finalization of its two audited pre-clinical carcinogenicity study reports. The Company evaluated the criteria under ASC 605-28 and concluded that the aforementioned milestone was substantive.

Under the U.S./RoW Agreement, the Company and AstraZeneca will share equally in the development costs of roxadustat not already paid for by Astellas, up to a total of $233.0 million (i.e. the Company’s share of development costs is $116.5 million, which was reached during the fourth quarter of 2015). Any additional development costs incurred by FibroGen during the development period in excess of the $233.0 million (aggregated spend) will be fully reimbursed by AstraZeneca. AstraZeneca will pay the Company tiered royalty payments on AstraZeneca’s future net sales (as defined in the agreement) of roxadustat in the low 20% range. In addition, the Company will receive a transfer price for delivery of commercial product based on a percentage of AstraZeneca’s net sales (as defined in the agreement) in the low- to mid-single digit range.

China Agreement

Effective July 30, 2013, the Company (through its subsidiaries affiliated with China) entered into a collaboration agreement with AstraZeneca for the development and commercialization (but not manufacture) of roxadustat for the treatment of anemia in China (“China Agreement”). Under the terms of the China Agreement, AstraZeneca agreed to pay upfront consideration totaling $28.2 million, which were fully received in 2014. In addition, the China Agreement provides for AstraZeneca to pay regulatory approval and other approval related milestones of up to $161.0 million. The China Agreement also provides for sales related milestone payments of up to $167.5 million and contingent payments of $20.0 million related to possible future compounds. The China Agreement is structured as a 50/50 profit or loss share (as defined) and provides for joint development costs (including capital and equipment costs for construction of the manufacturing plant in China), to be shared equally during the development.

In September 2016, AstraZeneca approved the protocol related to the development of roxadustat for the treatment of anemia in patients with myelodysplastic syndrome (“MDS”), for which the Company has received approval from the China Food and Drug Administration for its clinical trial application for a Phase 2/3 trial and acceptance of its Investigational New Drug Application from the U.S. Food and Drug Administration for a Phase 3 trial. As a result, for revenue recognition purposes, during the third quarter of 2016, the Company extended the estimated joint development service period for the AstraZeneca agreements from the end of 2018 to the end of 2020, to allow for development of MDS.

In October 2017, the China Food and Drug Administration accepted the Company’s recently submitted New Drug Application (“NDA”) for registration of roxadustat for anemia in dialysis-dependent CKD and non-dialysis-dependent CKD (NDD-CKD) patients. This NDA submission triggered a $15.0 million milestone payment to the Company by AstraZeneca, which has been received and fully recognized under the Company’s current revenue recognition policy as license and milestone revenue in the fourth quarter of 2017.

Accounting for the Astellas Agreements

For each of the Astellas agreements, the Company has evaluated the deliverables within the respective arrangements and has separated them into various units of accounting.

Deliverables that did not provide standalone value have been combined with other deliverables to form a unit of accounting that collectively has standalone value, with revenue being recognized on the combined unit of accounting, rather than the individual deliverables. There are no right-of-return provisions for the delivered items in the Astellas agreements.

For the Astellas agreements, the Company allocated arrangement consideration to various units of accounting based on BESP of each deliverable within each unit of accounting using the relative selling price method as the Company did not have VSOE or TPE of selling price for such deliverables. Arrangement consideration includes non-contingent upfront payments of $360.1 million and cumulative co-development billings of $151.7 million (for Europe Agreement) as of December 31, 2017.

For the technology license under the Japan Agreement and Europe Agreement, BESP was determined primarily by using the discounted cash flow (“DCF”) method, which aggregates the present value of future cash flows to determine the valuation as of the effective date of each of the agreements. The DCF method involves the following key steps: 1) the determination of cash flow forecasts and 2) the selection of a range of comparative risk-adjusted discount rates to apply against the cash flow forecasts. The discount rates selected were based on expectations of the total rate of return, the rate at which capital would be attracted to the Company and the level of risk inherent within the Company. The discounts applied in the DCF analysis ranged from 17.5% to 20.0%. The Company’s cash flow forecasts were derived from probability-adjusted revenue and expense projections by territory. Such projections included consideration of taxes and cash flow adjustments. The probability adjustments were made after considering the likelihood of technical success at various stages of clinical trials and regulatory approval phases. BESP also considered certain future royalty payments associated with commercial performance of the Company’s compounds, transfer prices and expected gross margins.

The units of accounting that were analyzed, along with their general timing of delivery or performance of service and general timing of revenue recognition, are as follows:

•

License to the Company’s technology existing at the effective date of the agreements. For both of the Astellas agreements, the license was delivered at the beginning of the agreement terms, or when the agreements were signed, and any contingencies had been removed. In both cases, the Company concluded at the time of the agreement that its collaboration partner, Astellas, would have the knowledge and capabilities to exploit the licenses without the Company’s further involvement. However, the Japan Agreement with Astellas has contractual limitations that might affect Astellas’ ability to exploit the license and therefore, potentially, the conclusion as to whether the license provides stand-alone value. In the Japan agreement, Astellas does not have the right to manufacture commercial supplies of the drug. In order to determine whether this characteristic of the agreement should lead to a conclusion that the license did not have stand-alone value, the Company considered the intent of the parties and the substantive reasons that led to that feature of the agreement.

•

Manufacturing rights. In the case of the Japan Agreement, the Company retained manufacturing rights largely because of the way the parties chose for FibroGen to be compensated under the agreement. At the time the agreement was signed, the Company believed that it was more advantageous upon commercialization to have a transfer price revenue model in place as opposed to a traditional sales-based model. The Company and Astellas could have structured the arrangement with a transfer of manufacturing rights and compensated the Company through a royalty or other feature without significantly diminishing the prospects of the drug product. Therefore, the Company determined that the license in Japan provides stand-alone value to the customer despite the lack of manufacturing rights.

•

License to the Company’s technology developed during the term of the agreement and development (referred to as “when and if available”) and information sharing services. These deliverables are generally delivered throughout the term of the agreements and are recognized as revenue as the services are provided.

•

Co-development services (Europe Agreement). This deliverable relates to co-development services that were reasonably expected to be performed by the Company at the time the collaboration agreement was signed. Revenue is recognized as reimbursements for such co-development services are earned. The period related to this deliverable represented the Company’s determination of the non-contingent performance period, which was estimated to be 36 months for the Europe Agreement from the signing of the agreement. There was no provision for co-development services in the Japan agreement.

•

Manufacturing of clinical supplies of products. This deliverable is satisfied as supplies for clinical product are delivered for use in the Company’s clinical trial programs during the development period, or pre-commercialization period. Revenue is recognized based on the estimated proportion of the development services performed during the development period. These estimates are made at the beginning of each accounting period and will likely change throughout the course of the terms of both agreements. As new information related to these estimates becomes available, the Company may adjust the timing of revenue recognition related to this unit of accounting.

•

Manufacturing commercial supplies of products. This deliverable is satisfied and revenue is recognized as supplies are shipped for commercial use during the commercialization period. As this deliverable is considered a contingent deliverable, it is outside the scope of the initial allocation of upfront and other consideration.

•	Committee service. This deliverable is satisfied and revenue is recognized throughout the course of the various agreements as meetings are attended.

Any consideration received for each Astellas agreement after the initial proceeds on the agreement signing date were also (and will be also) allocated to the various units of accounting above per agreement using the relative selling price method under ASC 605-25.

Under the Japan Agreement, the Company is also eligible to receive from Astellas an aggregate of approximately $132.5 million in potential milestone payments, comprised of (i) up to $22.5 million in substantive milestone payments upon achievement of specified clinical and development milestone events, (ii) up to $95.0 million in substantive milestone payments upon achievement of specified regulatory milestone events, and (iii) up to approximately $15.0 million in milestone payments upon the achievement of specified commercial sales milestone.

Under the Europe Agreement, the Company is also eligible to receive from Astellas an aggregate of approximately $425.0 million in potential milestone payments, comprised of (i) up to $90.0 million in substantive milestone payments upon achievement of specified clinical and development milestone events, (ii) up to $335.0 million in substantive milestone payments upon achievement of specified regulatory milestone events, including up to $25.0 million in milestone payments in connection with receipt of marketing approval in Russia.

Accounting for the AstraZeneca Agreements

The Company evaluated whether the U.S./RoW and China Agreements should be accounted for as a single arrangement and concluded that the agreements should be accounted for as a single arrangement with the presumption that two or more agreements executed with a single customer at or around the same time should be presumed to be a single arrangement. Accordingly, upfront and other non-contingent arrangement consideration received and to be received has been and will be pooled together and allocated to each of the units of accounting in both the U.S./RoW and China Agreements based on their relative fair values.

The Company evaluated the deliverables within the arrangement and has separated them into various units of accounting. Deliverables that did not provide stand-alone value have been combined with other deliverables to form a unit of accounting that collectively has stand-alone value, with revenue being recognized on the combined unit of accounting, rather than the individual deliverables. There are no right-of-return provisions for the delivered items in the agreements.

For the technology license under the AstraZeneca U.S./RoW Agreement, BESP was determined based on a two-step process. The first step involved determining an implied royalty rate that would result in the net present value of future cash flows to equal to zero (i.e. where the implied royalty rate on the transaction would equal the target return for the investment). This results in an upper bound estimation of the magnitude of royalties that a hypothetical acquirer would reasonably pay for the forecasted cash flow stream. The Company’s cash flow forecasts were derived from probability-adjusted revenue and expense projections. Such projections included consideration of taxes and cash flow adjustments. The probability adjustments were made after considering the likelihood of technical success at various stages of clinical trials and regulatory approval phases. The second step involved applying the implied royalty rate, which was determined to be 40%, against the probability-adjusted projected net revenues by territory and determining the value of the license as the net present value of future cash flows after adjusting for taxes. The discount rate utilized was 17.5%.

U.S./RoW Agreement:

The units of accounting that were analyzed, along with their general timing of delivery or performance of service and general timing of revenue recognition, are as follows:

•

License to the Company’s technology existing at the effective date of the agreements. For the U.S./RoW Agreement, the license was delivered at the beginning of the agreement terms as all contingencies had been removed. The Company concluded that AstraZeneca has the knowledge and capabilities to exploit the U.S./RoW license without the Company’s further involvement.

•

Co-development services. This deliverable relates to co-development services which were reasonably expected to be performed by the Company at the time the Agreement was signed. Revenue is recognized as reimbursements for such co-development services are earned. The period related to this deliverable represented the Company’s determination of the non-contingent performance period, which was estimated to be 89 months from the signing of the U.S./RoW Agreement.

•

Manufacturing of clinical supplies of products. This deliverable is satisfied as supplies for clinical product are delivered for use in the Company’s clinical trial programs during the development period, or pre-commercialization period. Revenue is recognized based on the estimated proportion of the development services performed during the development period. These estimates are made at the beginning of each accounting period and will likely change throughout the course of the agreements. As new information related to these estimates becomes available, the Company may adjust the timing of revenue recognition related to this unit of accounting.

•

•	Committee service. This deliverable is satisfied and revenue is recognized throughout the course of the various agreements as meetings are attended.

Under the terms of the U.S./RoW Agreement, AstraZeneca has agreed to pay upfront, non-contingent and time-based payments totaling $374.0 million. Out of this amount, $82.0 million was determined to be fixed and determinable upon the execution of the collaboration agreement. Out of the remaining payments of $292.0 million, which are contractually due, $230.0 million had extended payment terms and, accordingly, were not considered to be fixed or determinable upon the execution of the agreement. As such, for these remaining payments, the amount of revenue recognized was limited to the amount of cash consideration received; additionally, for each of the amounts received, the amount of revenue recognized was determined on the basis of applying the relative selling price method to each of the units of accounting underlying the agreement. Further, $62.0 million of the remaining payment was contingent upon the occurrence of a specified event and accordingly was also not considered fixed or determinable. The payments of totaling $374.0 million were fully received in various amounts through June 2016.

Under the U.S./RoW Agreement, the Company is also eligible to receive from AstraZeneca an aggregate of approximately $875.0 million in potential milestone payments, comprised of (i) up to $65.0 million in substantive milestone payments upon achievement of specified clinical and development milestone events, (ii) up to $325.0 million in substantive milestone payments upon achievement of specified regulatory milestone events, (iii) up to $160.0 million in non-substantive deferred approval milestone, which would be paid if certain competitors do not launch an HIF compound in the U.S. on or before January 1, 2023 and (iv) up to approximately $325.0 million in milestone payments upon the achievement of specified commercial sales events.

China Agreement:

The units of accounting that were analyzed, along with their general timing of delivery or performance of service and general timing of revenue recognition, are as follows:

•

License to the Company’s technology existing at the effective date of the agreement. The license was delivered at the beginning of the agreement term as all contingencies had been removed. However, the China Agreement with AstraZeneca has contractual limitations that might affect AstraZeneca’s ability to exploit the license and therefore, potentially, the conclusion as to whether the license provides stand-alone value. In the China Agreement, AstraZeneca does not have the right to manufacture commercial supplies of the drug. In order to determine whether this characteristic of the arrangement should lead to a conclusion that the license did not have stand-alone value, the Company considered the intent of the parties and the substantive reasons that led to that feature of the agreement.

For the China Agreement, the Company retained manufacturing rights as an essential part of a strategy to pursue domestic regulatory pathway for product approval which requires the regulatory licensure of the manufacturing facility in order to commence commercial shipment. The prospects for the collaboration as a whole would have been substantially different had manufacturing rights been provided to AstraZeneca. Because the retention of manufacturing rights by the Company was a significant factor in the collaboration strategy, rather than simply a mechanism to properly compensate FibroGen, management concluded that the license and development services do not have stand-alone value apart from the manufacturing rights. Accordingly, all the deliverables identified, including co-development services, under the China Agreement have been treated as a single unit of account and all revenue allocable to this unit of account is deferred until delivery of commercial drug product has begun. Upon commencement of delivery of commercial drug product, revenue would be recognized in a pattern consistent with estimated deliveries of the commercial drug product.

Under the terms of the China Agreement, AstraZeneca agreed to pay upfront consideration totaling $28.2 million, of which $16.2 million was received as of December 31, 2013 and was determined to be fixed and determinable upon the execution of the collaboration agreement. The remainder of the upfront payments of $12.0 million had extended payment terms and, accordingly, was not considered to be fixed or determinable upon the execution of the agreement. This payment of $12.0 million was received as of March 31, 2014.

Under the China Agreement, the Company is also eligible to receive from AstraZeneca an aggregate of approximately $348.5 million in potential milestone payments, comprised of (i) up to $15.0 million in substantive milestone payments upon achievement of specified clinical and development milestone events, (ii) up to $146.0 million in substantive milestone payments upon achievement of specified regulatory milestone events, and (iii) up to approximately $187.5 million in milestone payments upon the achievement of specified commercial sales and other events.

As the Company is accounting for both the U.S./RoW and China Agreements as one arrangement, any consideration received after the initial proceeds on the agreement signing date were also (and will be also) allocated to the various units of accounting above using the relative selling price method under ASC 605-25.

Summary of revenue recognized under the collaboration agreements

The table below summarizes the accounting treatment for the various deliverables pursuant to each of the Astellas and AstraZeneca agreements. License amounts identified below are included in the “License and milestone revenue” line item in the consolidated statements of operations. All other elements identified below are included in the “Collaboration services and other revenue” line item in the consolidated statements of operations.

Amounts recognized as revenue under the Japan Agreement are shown below (in thousands):

		Years Ended December 31,
Agreement	Deliverable	2017		2016		2015
Japan	License	$	1,310	$	3,465	$	1,024
	Milestones		—		10,000		—
	Total license and milestone revenue	$	1,310	$	13,465	$	1,024
	Collaboration services revenue*	$	64	$	166	$	198

When and if available compounds, manufacturing — clinical supplies and committee services have each been identified as separate units of accounting with standalone value and amounts allocable to these elements have been recognized and classified within the Collaboration services revenue line item within the consolidated statements of operations.

The total arrangement consideration has been allocated to each of the following deliverables under the Japan Agreement, along with any associated deferred revenue as follows (in thousands):

	Cumulative Revenue Through December 31, 2017		Deferred Revenue at December 31, 2017		Total Consideration Through December 31, 2017
License	$	47,020	$	—	$	47,020
When and if available compounds		25		24		49
Manufacturing--clinical supplies		2,180		—		2,180
Committee services		21		—		21
Total license and collaboration services revenue	$	49,246	$	24	$	49,270

Amounts recognized as revenue under the Europe Agreement were as follows (in thousands):

		Years Ended December 31,
Agreement	Deliverable	2017		2016		2015
Europe	License	$	13,997	$	10,956	$	17,677
	Milestones		—		—		—
	Total license and milestone revenue	$	13,997	$	10,956	$	17,677
	Collaboration services revenue*	$	1,514	$	1,191	$	2,697

When and if available compounds, manufacturing — clinical supplies, development services — in progress at the time of signing of the agreement, and committee services have each been identified as a separate unit of accounting with standalone value and amounts allocable to these units have been recognized in revenue as services are performed and classified within the Collaboration services revenue line item within the consolidated statements of operations.

The total arrangement consideration has been allocated to each of the following deliverables under the Europe Agreement, along with any associated deferred revenue as follows (in thousands):

	Cumulative Revenue Through December 31, 2017		Deferred Revenue at December 31, 2017		Total Consideration Through December 31, 2017
License	$	426,270	$	—	$	426,270
When and if available compounds		423		388		811
Manufacturing--clinical supplies		10,210		—		10,210
Development services--in progress		34,153		—		34,153
Committee services		295		—		295
Total license and collaboration services revenue	$	471,351	$	388	$	471,739

Amounts recognized as revenue under the U.S./RoW and China Agreements were as follows (in thousands):

		Years Ended December 31,
Agreement	Deliverable	2017		2016		2015
U.S. / RoW and China	License	$	65,749	$	112,931	$	114,392
	Milestones		15,000		—		15,000
	Total license and milestone revenue	$	80,749	$	112,931	$	129,392
	Collaboration services revenue*	$	28,010	$	40,738	$	29,731
	China single unit of accounting**	$	—	$	—	$	—

Co-development, information sharing, and committee services have been combined into a single unit of accounting because the requirements to share information and serve on committees are useful only in combination with the development services, and because all three items are delivered over the same period while manufacturing — clinical supplies has been identified as a separate unit of accounting with standalone value and amounts allocable to this unit of accounting have been recognized and classified within the Collaboration services revenue line item within the consolidated statements of operations.

All revenues attributable to the China unit of accounting are deferred until all deliverables are met. The China license and collaboration services elements have been combined into a single unit of accounting and consideration allocable to this unit is being deferred due to FibroGen’s retention of manufacturing rights and lack of standalone value.

The total arrangement consideration has been allocated to each of the following deliverables under the U.S./RoW and China Agreements, along with any associated deferred revenue as follows (in thousands):

	Cumulative Revenue Through December 31, 2017		Deferred Revenue at December 31, 2017		Total Consideration Through December 31, 2017
License	$	468,446	$	—	$	468,446
Co-development, information sharing & committee services		118,679		23,744		142,423
Manufacturing--clinical supplies		463		24		487
China-single unit of accounting		—		96,019		96,019
Total license and collaboration services revenue	$	587,588	$	119,787	$	707,375

Other Revenues

Other revenues consist primarily of collagen material sold for research purposes. Other revenues were immaterial for each of the three years ended December 31, 2017.

Deferred Revenue

Deferred revenue represents amounts billed to the Company’s collaboration partners for which the related revenues have not been recognized because one or more of the revenue recognition criteria have not been met. The current portion of deferred revenue represents the amount to be recognized within one year from the balance sheet date based on the estimated performance period of the underlying deliverables. The long term portion of deferred revenue represents amounts to be recognized after one year through the end of the non-contingent performance period of the underlying deliverables. The long term portion of deferred revenue also includes amounts allocated to the China unit of accounting under the AstraZeneca arrangement as revenue recognition associated with this unit of accounting is tied to the commercial launch of the products within China, which is not expected to occur within the next year.

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

4.	Fair Value Measurements

In accordance with the authoritative guidance on fair value measurements and disclosures under U.S. GAAP, the Company presents all financial assets and liabilities and any other assets and liabilities that are recognized or disclosed at fair value on a nonrecurring basis. The guidance defines fair value, establishes a framework for measuring fair value in generally accepted accounting principles and expands disclosures about fair-value measurements. The guidance also requires fair value measurements be classified and disclosed in one of the following three categories:

Level 1: Quoted prices in active markets for identical assets or liabilities.

Level 2: Observable inputs other than quoted prices in active markets for identical assets or liabilities.

Level 3: Unobservable inputs.

The Company values certain assets and liabilities, focusing on the inputs used to measure fair value, particularly in instances where the measurement uses significant unobservable (Level 3) inputs. The Company’s financial instruments are valued using quoted prices in active markets (Level 1) or based upon other observable inputs (Level 2). The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and considers factors specific to the asset or liability. In addition, the categories presented do not suggest how prices may be affected by the size of the purchases or sales, particularly with the largest highly liquid financial issuers who are in markets continuously with non-equity instruments, or how any such financial assets may be impacted by other factors such as U.S. government guarantees. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement.

The fair values of the Company’s financial assets that are measured on a recurring basis are as follows (in thousands):

	December 31, 2017
	Level 1		Level 2		Level 3		Total
Corporate bonds	$	—	$	53,943	$	—	$	53,943
Bond and mutual funds		18,402		—		—		18,402
Equity investments		221		—		—		221
Money market funds		569,942		—		—		569,942
Total	$	588,565	$	53,943	$	—	$	642,508

	December 31, 2016
	Level 1		Level 2		Level 3		Total
Corporate bonds	$	—	$	126,683	$	—	$	126,683
Bond and mutual funds		22,462		—		—		22,462
Equity investments		225		—		—		225
Money market funds		94,543		—		—		94,543
Certificate of deposits		—		1,037		—		1,037
Total	$	117,230	$	127,720	$	—	$	244,950

The Company’s Level 2 investments are valued using third-party pricing sources. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar investments, issuer credit spreads, benchmark investments, prepayment/default projections based on historical data and other observable inputs.

The fair values of the Company’s financial liabilities that are carried at historical cost are as follows (in thousands):

	December 31, 2017
	Level 1		Level 2		Level 3		Total
Lease financing obligations	$	—	$	—	$	98,476	$	98,476

	December 31, 2016
	Level 1		Level 2		Level 3		Total
Lease financing obligations	$	—	$	—	$	97,856	$	97,856

The fair value of the Company’s financial liabilities were each derived by using an income approach which required Level 3 inputs such as discounted estimated future cash flows.

There were no transfers of assets or liabilities between levels for the years ended December 31, 2017, 2016 or 2015.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Balance Sheet Components

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Components

5.	Balance Sheet Components

Cash and Cash Equivalents

Cash and cash equivalents consisted of the following (in thousands):

	December 31,
	2017		2016
Cash	$	103,716	$	79,239
Money market funds		569,942		94,543
Total cash and cash equivalents	$	673,658	$	173,782

Property and Equipment

Property and equipment consisted of the following (in thousands):

	December 31,
	2017			2016
Laboratory equipment	$	19,497		$	18,533
Computer equipment		6,006			5,678
Furniture and fixtures		5,575			5,533
Leasehold improvements		93,758			93,564
Building shell (Refer to Note 8)		53,879			53,879
Construction in progress		10,402			109
Total property and equipment	$	189,117		$	177,296
Less: accumulated depreciation		(59,641	)		(53,639	)
Property and equipment, net	$	129,476		$	123,657

Depreciation expense for the years ended December 31, 2017, 2016 and 2015 was $6.1 million, $6.0 million, and $5.7 million, respectively.

Investments

All investments are classified as available-for-sale. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s available-for-sale investments by major investments type are summarized in the tables below (in thousands):

	December 31, 2017
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Corporate bonds	$	53,985	$	4	$	(46	)	$	53,943
Bond and mutual funds		17,249		1,153		—			18,402
Equity investments		126		95		—			221
Total investments	$	71,360	$	1,252	$	(46	)	$	72,566

	December 31, 2016
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Corporate bonds	$	126,550	$	182	$	(49	)	$	126,683
Certificate of deposits		1,037		—		—			1,037
Bond and mutual funds		22,305		157		—			22,462
Equity investments		125		100		—			225
Total investments	$	150,017	$	439	$	(49	)	$	150,407

The contractual maturities of available-for-sale investments were as follows (in thousands):

	December 31, 2017
Within one year	$	53,943
After one year through four years		—
Total debt investments		53,943
Bond and mutual funds		18,402
Equity investments		221
Total investments	$	72,566

Available-for-sale investments are reported at fair value and as such, their associated unrealized gains and losses are reported as a separate component of stockholders’ equity within accumulated other comprehensive income (loss).

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31,
	2017		2016
Preclinical and clinical trial accruals	$	32,321	$	29,550
Payroll and related accruals		18,810		14,232
Property taxes and other		4,201		451
Professional services		1,991		1,252
Other		6,458		5,429
Total accrued liabilities	$	63,781	$	50,914

Product Development Obligations

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Product Development Obligations

6.	Product Development Obligations

The Technology Development Center of the Republic of Finland (“TEKES”) product development obligations consist of 11 separate advances (each in the form of a note agreement) received by FibroGen Europe between 1996 and 2008 from TEKES. These advances are granted on a project by project basis to fund various product development efforts undertaken by FibroGen Europe only. Each separate note bears interest (not compounded) calculated as one percentage point less than the Bank of Finland rate in effect at the time of the note, but no less than 3.0%.

If the research work funded by TEKES does not result in an economically profitable business or does not meet its technological objectives, TEKES may, on application from FibroGen Europe, forgive each of these loans, including accrued interest, either in full or in part. As of December 31, 2017 and 2016, the Company had $11.3 million and $9.9 million of principal outstanding, respectively, and $5.9 million and $4.9 million of interest accrued, respectively, which were presented in the product development obligations line on the consolidated balance sheets.

The Company is not a guarantor of these loans, and these loans are not repayable by FibroGen Europe until it has distributable funds.

Convertible Note Payable

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Convertible Note Payable

7.	Convertible Note Payable

In January 2013, FibroGen China entered into a $0.6 million convertible promissory note. The note bears simple interest at a rate of two percent (2.00%) per annum, accrued on an annual basis in arrears. The outstanding principal balance and unpaid accrued interest on the note is due and payable upon the earlier of (a) the effectiveness of the initial public offering of FibroGen China or (b) the eight year anniversary of the date of the note. The total outstanding principal balance and unpaid accrued interest on the note will be converted into Series A Preferred Stock of FibroGen China at the option of the lender or by the Company at its discretion.

Commitment and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

8.	Commitments and Contingencies

Operating Leases

Future minimum lease payments under all non-cancelable operating lease obligations as of December 31, 2017 are as follows (in thousands):

Year Ending	Operating Leases
2018	$	445
2019		310
2020		155
2021		25
2022		16
Total minimum payments	$	951

Facility Lease Financing Obligations

FibroGen, Inc.

In September 2006, the Company entered into a long-term property lease with Shorenstein Properties LLC (“Alexandria” or “landlord”) providing the Company with 234,249 square feet of space for an initial term of 15 years. Upon signing, a stand-by letter of credit was established in the amount of $7.3 million which has been included in restricted time deposits. Starting the fourth quarter of 2016, on an annual basis, 1/8^th of this letter of credit was released. As a result, the restriction of a $1.0 million was removed, and the amount was reclassified from restricted time deposits to short-term investment during the fourth quarter of 2016 and 2017, respectively. The agreement included an expansion option to occupy part of an adjacent building within 31 months of the lease commencement date of November 20, 2008. In June 2012, the Company gave notice to its landlord that it would not exercise this expansion option, which resulted in a $5.0 million payment liability to the landlord which is being financed over the remaining lease term of its lease.

In connection with this lease, the Company was responsible for approximately 60% of the construction costs for the tenant improvements. The Company is deemed, for accounting purposes only, to be the accounting owner of the entire project including the building shell, even though it is not the legal owner. The balance of the tenant improvements were paid by Alexandria in the form of a tenant improvement allowance of $140.50 per square foot of rentable space, or $32.5 million.

In connection with the Company’s accounting for this transaction, the Company capitalized Alexandria’s costs of constructing the building shell which totaled $50.8 million, and recognized a corresponding lease financing obligation. The Company also recognized, as an additional lease financing obligation, the reimbursements totaling $32.5 million from landlord for tenant improvements since these reimbursements are also deemed to be a financing obligation.

A portion of the monthly lease payment is allocated to land rent and recorded as an operating lease expense and the non-interest portion of the amortized lease payments to the landlord related to rent of the building is applied to the lease financing liability.

In addition, the Company had a leased facility located in South San Francisco, California, which was used as its corporate headquarters prior to moving to its current facility in 2008. The South San Francisco facility is approximately 106,000 square feet and was fully subleased. This lease and associated subleases terminated in February 2015.

FibroGen China

In February 2013, the Company entered into a long-term property lease with Beijing Economic-Technological Development Area (“BDA”) Management Committee for a pilot plant located in Beijing Yizhuang Biomedical Park (“BYBP”) of BDA. The leased space is 4,820 square meters over an eight (8) year term starting February 1, 2013.

In connection with this lease, the Company was responsible for approximately 100% of the construction costs for the tenant improvements. The Company is deemed, for accounting purposes only, to be the accounting owner of the entire project, including the building shell, even though it is not the legal owner.

In connection with the Company’s accounting for this transaction, the Company capitalized BDA Management Committee’s costs of constructing the building shell which totaled $3.1 million, and recognized a corresponding lease financing obligation. The Company also recognized, as an additional lease financing obligation, the reimbursements totaling $0.5 million from BYBP for a rent subsidy since this reimbursement is also deemed to be a financing obligation.

Future minimum lease payments, on a consolidated basis, under the Company’s facility lease financing obligations as of December 31, 2017 are as follows (in thousands):

Year Ending	Lease financing obligations
2018	$	14,250
2019		14,466
2020		14,687
2021		14,171
2022		14,335
Thereafter		12,873
Total minimum payments	$	84,782

Apart from the property leases with Alexandria and BDA Management Committee, rent expense for leased facilities under operating lease commitments was $3.0 million, $2.8 million, and $2.7 million for the years ended December 31, 2017, 2016 and 2015, respectively. The Company received sublease income of $3.9 million, $3.8 million, and $3.4 million for the years ended December 31, 2017, 2016 and 2015, respectively, which were recorded as a reduction of research and development expenses and general and administrative expenses for the respective periods.

Indemnification Agreements

The Company enters into standard indemnification arrangements in the ordinary course of business, including for example, service, manufacturing and collaboration agreements. Pursuant to these arrangements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified parties for losses suffered or incurred by the indemnified party, including in connection with intellectual property infringement claims by any third party with respect to its technology. The term of these indemnification agreements is generally perpetual any time after the execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these arrangements is not determinable. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements. As a result, the Company believes the estimated fair value of these arrangements is minimal.

The Company has entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the extent permissible under applicable law.

Equity and Stock-based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity and Stock-based Compensation

9.	Equity and Stock-based Compensation

Subsidiary Stock and Non-Controlling Interests

FibroGen Europe

As of December 31, 2017 and 2016, respectively, FibroGen Europe had a total of 42,619,022 shares of Preferred Stock outstanding, of which there were 1,700,845 shares of Series A Preferred Stock, 1,875,000 shares of Series B Preferred Stock, 1,599,503 shares of Series C Preferred Stock, 1,520,141 shares of Series D Preferred Stock, 459,565 shares of Series E Preferred Stock, 5,714,332 shares of Series F Preferred Stock, 9,927,500 shares of Series G Preferred Stock and 19,822,136 shares of Series H Preferred Stock, all of which shares no longer have any right to be exchanged for FibroGen, Inc. Common Stock.

The holders of FibroGen Europe’s shares of Preferred Stock (“Preferred Shares”) have the following rights, preferences and privileges:

Dividend Rights — When the assets of FibroGen Europe are distributed (except for distribution in a liquidation), Preferred Shares shall have the same rights to dividend or other forms of distribution as shares of Common Stock of FibroGen Europe. In the event of a merger, holders of Preferred Shares do not have the right to demand FibroGen Europe to redeem all or part of their Preferred Shares. FibroGen Europe may repurchase shares of Common Stock or Preferred Shares for consideration.

Pre-emptive Right — Preferred Shares shall have pre-emptive subscription right in accordance with the Finnish Limited Liability Companies Act if additional shares are issued, option rights are given, or convertible loan is taken, provided, however, that the foregoing pre-emptive right does not apply to a directed share issue, for which two thirds (2/3) of the voting shares represented at a general meeting of shareholders approve for an important legitimate cause.

Redemption Right — If a Preferred Share can be redeemed by a majority shareholder owning more than ninety percent (90%) of the shares of FibroGen Europe in accordance with the provisions of the Finnish Limited Liability Companies Act, the minority holders of Preferred Shares have the right to request redemption of their shares.

Voting Right — Each share has one vote. Preferred Shares have voting rights only in situations that are specifically provided in the Articles of Association, which include a merger transaction and directed share issue. In addition, Preferred Shares have right to vote in a general shareholder meeting for amending the Articles of Association if the amendment will affect the rights of Preferred Shares.

Conversion Right (1-for-1 basis into Common Stock of FibroGen Europe):

•

Voluntary conversion right: Preferred Shares can be converted into common shares upon the written request of a shareholder provided that the conversion is feasible within the maximum and minimum amounts of shares of classes of FibroGen Europe as set forth in its Articles of Association. Such request can be withdrawn before the notification of conversion is filed with the Finnish Trade Register.

•

Compulsory conversion right: Preferred Shares will be converted into common shares if (i) FibroGen Europe’s shares are listed in a stock exchange or other trading system in the European Economic Area, or (ii) FibroGen Europe’s recombinant collagen and gelatin production technology is being put into commercial use in the area of EU and certain other European states. Commercial use means there is income generated from the first commercial sale of the products incorporating the above mentioned technology and does not include license fees, development financing, milestone payments or income from test products or equipment used in research. The board of directors of FibroGen Europe shall notify the shareholders of the compulsory conversion in writing, and the shareholders shall request to convert their shares within the timeframe provided in the notification. Should the shareholders fail to make the conversion request within the time limit, FibroGen Europe may redeem the shares of such shareholders.

Liquidation Right — In the event of a dissolution of FibroGen Europe, holders of Preferred Shares are entitled to be paid in an amount equal to the subscription price of the shares before any distribution is made to holders of common shares. Among holders of Preferred Shares, holders of shares of Series F Preferred Stock are entitled to be paid in an amount equal to the subscription price of Series F Preferred Stock before any distribution is made to holders of other Preferred Shares.

FibroGen China

FibroGen China had 6,758,000 Series A Preference Shares outstanding as of December 31, 2017 and 2016, respectively. The holders of the FibroGen China Series A Preference Shares have the following rights, preferences and privileges:

Liquidation — In the event of liquidation, dissolution, or winding up of the Company, either voluntary or involuntary, including by means of a merger, the holders of FibroGen China Series A Preference Shares are entitled to be paid an amount equal to the product of the number of shares held by a holder of shares of FibroGen China Series A Preference Shares and the original issue price of $1.00 (subject to equitable adjustment for any stock dividend, combination, split, reclassification, recapitalization) plus all declared and unpaid dividends thereon.

Conversion — Each share of FibroGen China Series A Preference Shares is convertible into the number of fully paid and non-assessable shares of Common Stock of FibroGen China that results from dividing the original issue price by the conversion price in effect at the time of the conversion, subject to adjustments for stock splits, stock dividends, reclassifications and like events. The FibroGen China Series A Preference Shares have a conversion price that is equal to the original issuance price such that the conversion ratio to FibroGen China Common Stock is 1:1 as of all periods presented.

Voting — The holders of FibroGen China Series A Preference Shares are entitled to vote together with the FibroGen China Common Stock holders on all matters submitted for a vote of the stockholders. The holder of each share of FibroGen China Series A Preference Shares has the number of votes equal to the number of shares of FibroGen China Common Stock into which it is convertible.

Dividends — The holders of FibroGen China Series A Preference Shares are entitled to receive cash dividends when and if declared, at a rate of 6%.

Non-Controlling Interests

Non-controlling interest positions related to the issuance of subsidiary stock as described above are reported as a separate component of consolidated equity from the equity attributable to the Company’s stockholders at December 31, 2017 and 2016. In addition, the Company does not allocate losses to the non-controlling interests as the outstanding shares representing the non-controlling interest do not represent a residual equity interest in the subsidiary. Upon the initial public offering and as described above, all eligible FibroGen Europe preferred shares were exchanged for 958,996 shares of FibroGen Common Stock. No other FibroGen Europe shares have the right to be exchanged for FibroGen, Inc. Common Stock.

Common Stock

Each share of Common Stock is entitled to one vote. The holders of Common Stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors, subject to the prior rights of holders of all classes of stock outstanding.

Shares of Common Stock outstanding, shares of stock plans outstanding and shares reserved for future issuance related to stock options and RSUs grant and the Company’s Employee Stock Purchase Plan (“ESPP”) purchases are as follows (in thousands):

	December 31,
	2017		2016
Common stock outstanding		82,498		63,665
Stock options outstanding		11,550		13,660
RSUs outstanding		1,562		1,211
Common stock warrants outstanding		4		4
Shares reserved for future stock options and RSUs grant		4,190		4,032
Shares reserved for future ESPP offering		2,024		1,638
Total shares of common stock reserved		101,828		84,210

Stock Plans

Stock Option and RSU Plans

Under the Company’s Amended and Restated 2005 Stock Plan (“2005 Stock Plan”), the Company may issue shares of Common Stock and options to purchase Common Stock and other forms of equity incentives to employees, directors and consultants. Options granted under the 2005 Stock Plan may be incentive stock options or nonqualified stock options. Incentive stock options (“ISO”) may be granted only to employees and officers of the Company. Nonqualified stock options (“NSO”) and stock purchase rights may be granted to employees, directors and consultants. The board of directors has the authority to determine to whom options will be granted, the number of options, the term and the exercise price. Options are to be granted at an exercise price not less than fair market value for an ISO or an NSO. Options generally vest over four years. Options expire no more than 10 years after date of grant. Upon the effective date of the registration statement related to the Company’s initial public offering, the 2005 Plan was amended to cease the grant of any additional awards thereunder, although the Company will continue to issue common stock upon the exercise of previously granted stock options under the 2005 Plan.

In September 2014, the Company adopted a 2014 Equity Incentive Plan (the “2014 Plan”) which became effective on November 13, 2014. The 2014 Plan is the successor equity compensation plan to the 2005 Plan. The 2014 Plan will terminate on November 12, 2024. The 2014 Plan provides for the grant of incentive stock options, nonqualified stock options, restricted stock awards, stock appreciation rights, performance stock awards, performance cash awards, restricted stock units and other stock awards to employees, directors and consultants. Stock options granted must be at prices not less than 100% of the fair market value at date of grant. Option vesting schedules are determined by the Company at the time of issuance and generally have a four year vesting schedule (25% vesting on the first anniversary of the vesting base date and quarterly thereafter over the next 3 years). Options generally expire ten years from the date of grant unless the optionee is a 10% stockholder, in which case the term will be five years from the date of grant. Unvested options exercised are subject to the Company’s repurchase right. Shares reserved for issuance increases on January 1 of each year commencing on January 1, 2016 and ending on January 1, 2024 by the lesser of (i) the amount equal to 4% of the number of shares issued and outstanding on December 31 immediately prior to the date of increase or (ii) such lower number of shares as may be determined by the board of directors. As of December 31, 2017, the Company has reserved 4,190,412 shares of its common stock that remains unissued for issuance under the 2014 Plan.

Issuance of shares upon share option exercise or share unit conversion is made through issuance of new shares authorized under the plan.

Certain Common Stock option holders have the right to exercise unvested options, subject to a right held by the Company to repurchase the stock, at the original exercise price, in the event of voluntary or involuntary termination of employment of the stockholder. The shares are generally released from repurchase provisions ratably over four years. The Company accounts for the cash received in consideration for the early exercised options as a liability. At December 31, 2017 and 2016, no shares of Common Stock were subject to repurchase by the Company.

Stock option transactions, including forfeited options granted under the 2014 Plan as well as prior plans, are summarized below:

	Shares (In thousands)			Weighted Average Exercise per Share		Weighted Average Remaining Contractual Life (In Years)		Aggregate Intrinsic Value (In thousands)
Outstanding at December 31, 2016		13,660		$	11.35
Granted		1,923			26.95
Exercised		(3,827	)		8.10
Expired		(34	)		24.58
Forfeited		(172	)		22.05
Outstanding at December 31, 2017		11,550			14.82		5.80	$	376,670
Vested and expected to vest, December 31, 2017		11,550			14.82		5.80		376,670
Exercisable at December 31, 2017		8,319		$	10.98		4.71	$	303,049

The total intrinsic value of options exercised during the years ended December 31, 2017, 2016, and 2015 was $111.9 million, $17.9 million, and $48.7 million, respectively.

The following table summarizes RSU activity:

	Shares (In thousands)			Fair Value at Grant
Unvested at December 31, 2016		1,211		$	21.60
Granted		978			26.59
Vested		(563	)		21.34
Forfeited		(64	)		23.34
Unvested at December 31, 2017		1,562		$	24.75

Among the vested RSUs during the year ended December 31, 2017, 326,626 shares were released and issued, while the remaining was withheld for the related payroll taxes. The estimated weighted-average fair value of the awards granted during the years ended December 31, 2017, 2016 and 2015 was $26.59, $19.37 and $29.66, respectively.

ESPP

In September 2014, the Company adopted a 2014 ESPP which became effective on November 13, 2014. The 2014 ESPP is designed to enable eligible employees to periodically purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation, subject to any plan or IRS limitations. At the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last day of the offering period. Purchases are accomplished through participation in discrete offering periods. The 2014 ESPP is intended to qualify as an ESPP under Section 423 of the Internal Revenue Code. The Company has reserved 1,600,000 shares of its common stock for issuance under the 2014 ESPP and shares reserved for issuance increases January 1 of each year commencing January 1, 2016 by the lesser of (i) a number of shares equal to 1% of the total number of outstanding shares of common stock on December 31 immediately prior to the date of increase; (ii) 1,200,000 shares or (iii) such number of shares as may be determined by the board of directors. There were 250,834 shares, 266,720 shares and 315,385 shares purchased by employees under the 2014 Purchased Plan for the years ended December 31, 2017, 2016 and 2015, respectively.

The expected term of 2014 ESPP shares is the average of the remaining purchase periods under each offering period.

Stock-Based Compensation

Stock-based compensation expense allocated to research and development and general and administrative expense for the years ended December 31, 2017, 2016, and 2015 was as follows (in thousands):

	Years Ended December 31,
	2017		2016		2015
Research and development	$	21,807	$	19,070	$	16,987
General and administrative		15,732		13,062		10,694
Total stock-based compensation expense	$	37,539	$	32,132	$	27,681

The Company estimates the fair value of stock options using the Black-Scholes option valuation model. The fair value of employee stock options is being amortized on a straight-line basis over the requisite service period of the awards.

The Company, in making its determinations of the fair value of its Common Stock, considered a variety of quantitative and qualitative factors, including (i) net present value of the Company’s projected earnings, (ii) fair market value of the stock of comparable publicly-traded companies, (iii) any third party transactions involving the Company’s convertible preferred stock, (iv) liquidation preferences of the Company’s preferred stock and the likelihood of conversion of the preferred stock, (v) changes in the Company’s business operations, financial condition and results of operations over time, including cash balances and burn-rate, (vi) the status of new product development, and (vii) general financial market conditions. Subsequent to the IPO, the fair market value of common stock is based on the closing price of the Company’s common stock as reported on the NASDAQ Global Select Market on the date of the grant.

The fair value of employee stock options was estimated using the following assumptions:

Expected Term. Expressed as a weighted-average, the expected life of the options is based on the average period the stock options are expected to be outstanding and was based on the Company’s historical information of the option exercise patterns and post-vesting termination behavior as well as contractual terms of the instruments.

Expected Volatility. While the Company considers its historical data regarding the volatility of its Common Stock, the expected volatility is currently based upon the historical volatility of comparable public entities. In evaluating comparable companies, the Company considered factors such as industry, stage of life cycle, size and duration as a public company.

Risk-Free Interest Rate. Expressed as a weighted-average, the risk-free interest rate assumption is based on the U.S. Treasury instruments whose term was consistent with the expected term of the Company’s stock options.

Expected Dividend Yield. The Company has never declared or paid any cash dividends and does not plan to pay cash dividends in the foreseeable future.

The assumptions used to estimate the fair value of stock options granted and ESPPs using the Black-Scholes option valuation model were as follows:

	Years Ended December 31,
	2017			2016			2015
Stock Options
Expected term (in years)		5.7			5.3			5.2
Expected volatility		71.5	%		69.9	%		69.9	%
Risk-free interest rate		2.2	%		1.4	%		1.7	%
Expected dividend yield		—			—			—
Weighted average estimated fair value	$	16.96		$	11.49		$	16.12

ESPPs
Expected term (in years)	0.5 - 2.0			0.5 - 2.0			0.4 - 2.0
Expected volatility	52.8 - 77.2		%	61.9 - 80.7		%	58.5 - 69.0		%
Risk-free interest rate	0.5 - 1.6		%	0.2 - 1.0		%	0.1 - 0.6		%
Expected dividend yield		—			—			—
Weighted average estimated fair value	$	9.41		$	9.94		$	13.03

As of December 31, 2017, there was $37.6 million of total unrecognized compensation costs, net of estimated forfeitures, related to non-vested stock option awards granted that will be recognized on a straight-line basis over the weighted-average period of 2.39 years. As of December 31, 2017, there was $29.6 million of total unrecognized compensation costs, net of estimated forfeitures, related to non-vested RSUs granted that will be recognized on a straight-line basis over the weighted-average period of 2.70 years.

Warrants

The following warrants to purchase shares of Common Stock were issued in connection with certain facility and equipment lease financing arrangements and are outstanding at December 31, 2017:

Year of Issuance	Number of Shares		Exercise Price per Share		Reason for Issuance	Expiration Date
2000		4,430	$	15.00	Issued in connection with lease agreement	Five years after initial public offering or upon merger or sale of the Company’s assets, whichever occurs first
		4,430

Net Loss Per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Loss Per Share

10.	Net Loss Per Share

The following securities were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive for the three years presented (in thousands):

	Years Ended December 31,
	2017		2016		2015
Employee stock options		11,550		13,660		13,583
RSUs outstanding		1,562		1,211		865
Warrants		4		4		7
		13,116		14,875		14,455

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

12.	Income Taxes

The components of loss before income taxes are as follows (in thousands):

	Years Ended December 31,
	2017			2016			2015
Domestic	$	(101,234	)	$	(38,156	)	$	(66,411	)
Foreign		(24,648	)		(23,595	)		(19,126	)
Loss before provision for income taxes	$	(125,882	)	$	(61,751	)	$	(85,537	)

The provision for (benefit from) income taxes consists of the following (in thousands):

	Years Ended December 31,
	2017		2016			2015
Current:
Federal	$	—	$	—		$	—
State		2		2			2
Foreign		319		139			240
Total current	$	321	$	141		$	242
Deferred:
Federal	$	—	$	(212	)	$	—
State		—		—			—
Foreign		—		—			—
Total deferred	$	—	$	(212	)	$	—
Total provision for (benefit from) income taxes	$	321	$	(71	)	$	242

The following is the reconciliation between the statutory federal income tax rate and the Company’s effective tax rate:

	Years Ended December 31,
	2017			2016			2015
Tax at statutory federal rate		34.0	%		34.0	%		34.0	%
State tax		—	%		—	%		—	%
Stock-based compensation expense		18.5	%		(7.9	)%		(4.6	)%
Change in deferred tax assets due to rate change		43.9	%		—	%		—	%
Change in valuation allowance due to rate change		(43.9	)%		—	%		—	%
Net operating losses not benefitted		(43.8	)%		(12.9	)%		(21.7	)%
Foreign net operating losses benefitted		(6.7	)%		(13.0	)%		(7.6	)%
Orphan drug credit		(2.0	)%		—	%		—	%
Other		(0.3	)%		(0.1	)%		(0.4	)%
Total		(0.3	)%		0.1	%		(0.3	)%

Significant components of the Company’s deferred tax assets are as follows (in thousands):

	December 31,
	2017			2016
Federal and state net operating loss carryforwards	$	71,256		$	42,900
Tax credit carryforwards		39,488			29,846
Foreign net operating loss carryforwards		15,052			11,704
Stock-based compensation		7,835			11,231
Lease obligations		2,737			4,414
Reserves and accruals		4,851			5,465
Deferred revenue		18,103			22,909
Other		420			741
Subtotal		159,742			129,210
Less: Valuation allowance		(159,540	)		(128,995	)
Net deferred tax assets		202			215

Fixed assets		(181	)		(122	)
Other		(21	)		(93	)
Net deferred tax liabilities		(202	)		(215	)
Total net deferred tax assets	$	—		$	—

A valuation allowance has been provided to reduce the deferred tax assets to an amount management believes is more likely than not to be realized. Expected realization of the deferred tax assets for which a valuation allowance has not been recognized is based on upon the reversal of existing temporary differences and future taxable income.

The valuation allowance increased by $30.5 million, $12.3 million and $22.0 million for the years ended December 31, 2017, 2016 and 2015, respectively. Due to uncertainty surrounding the realization of the favorable tax attributes in the future tax returns, the Company has established a valuation allowance against its otherwise recognizable net deferred tax assets.

At December 31, 2017, the Company had net operating loss carryforwards available to offset future taxable income of approximately $306.0 million and $143.4 million for federal and state tax purposes, respectively. These carryforwards will begin to expire in 2026 for federal and 2018 for state purposes, if not utilized before these dates. The Company also had foreign net operating loss carryforwards of approximately $63.5 million which expire between 2018 and 2027 if not utilized.

At December 31, 2017, the Company had approximately $38.8 million of federal and $22.9 million of California research and development tax credit and other tax credit carryforwards available to offset future taxable income. The federal credits begin to expire in 2018 and the California research credits have no expiration dates.

On December 22, 2017, the Tax Cuts and Jobs Act (“Tax Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as. The Company has calculated its best estimate of the impact of the Tax Act in accordance with our understanding of the Tax Act and guidance available as of the issuance of the consolidated financial statements. The tax rate decrease resulted in a reduction of $55.2 million in the Company’s deferred tax assets, and a corresponding decrease of the same amount in the valuation allowance against these deferred tax assets, as substantially all of the Company’s U.S. and foreign deferred tax assets, net of deferred tax liabilities, are subject to a full valuation allowance.

Due to the adoption of ASU 2016-09 in 2017, the Company recorded a retrospective increase of $19.5 million in the deferred tax assets for previously unrecognized excess tax benefits that existed as of December 31, 2016, and a corresponding increase of $19.5 million in the valuation allowance against these deferred tax assets. In addition, all excess tax benefits and deficiencies are recognized as income tax expense and will result in increased volatility in the Company’s income tax.

Federal and state tax laws impose substantial restrictions on the utilization of net operating loss and credit carryforwards in the event of an “ownership change” for tax purposes, as defined in IRC Section 382. The Company reviewed its stock ownership for year ended December 31, 2017 and concluded no ownership changes occurred which would result in a reduction of its net operating loss or in its research and development credits expiring unused. If additional ownership change occurs, the utilization of net operating loss and credit carryforwards could be significantly reduced.

Uncertain Tax Positions

The Company had unrecognized tax benefits of approximately $23.3 million as of December 31, 2017. Approximately $0.4 million of unrecognized tax benefits, if recognized, would affect the effective tax rate. The interest accrued as of December 31, 2017 and 2016 was immaterial.

A reconciliation of the beginning and ending amounts of unrecognized income tax benefits during the three years ended December 31, 2017 is as follows (in thousands):

	Federal and State
Balance as of December 31, 2014	$	19,122
Decrease due to prior positions		(2,382	)
Increase due to current year position		7,473
Balance as of December 31, 2015		24,213
Decrease due to prior positions		(7,109	)
Increase due to current year position		2,550
Balance as of December 31, 2016		19,654
Increase due to prior positions		303
Increase due to current year position		5,448
Decrease due to U.S. tax rate change		(2,044	)
Balance as of December 31, 2017	$	23,361

Unrecognized tax benefits may change during the next twelve months for items that arise in the ordinary course of business. The Company does not anticipate a material change to its unrecognized tax benefits over the next twelve months that would affect the Company’s effective tax rate.

The Company classifies interest and penalties as a component of tax expense, if any.

The Company files income tax returns in the U.S. federal jurisdiction, U.S. state and other foreign jurisdictions. The U.S. federal and U.S. state taxing authorities may choose to audit tax returns for tax years beyond the statute of limitation period due to significant tax attribute carryforwards from prior years, making adjustments only to carryforward attributes. The foreign statute of limitation generally remains open from 2008 to 2017. The Company is not currently under audit in any tax jurisdiction.

Related Party Transactions

12 Months Ended

Dec. 31, 2017

Related Party Transactions

13.	Related Party Transactions

Astellas is an equity investor in the Company and considered a related party. During the years ended December 31, 2017, 2016 and 2015, the Company recorded revenue related to collaboration agreements with Astellas of $16.9 million, $25.8 million, and $21.6 million, respectively. During the years ended December 31, 2017, 2016 and 2015, the Company recorded expense related to collaboration agreements with Astellas of $1.0 million, $6.4 million and $9.8 million, respectively.

As of December 31, 2017 and 2016, accounts receivable from Astellas were $4.0 million and $4.1 million, respectively, and amounts due to Astellas were $0.3 million and $1.6 million, respectively. The amounts due are included in accrued liabilities on the consolidated balance sheets.

Julian N. Stern, a director of the Company from November 1996 through June 2017, is currently serving as corporate secretary of the Company and is of counsel to the law firm of Goodwin Procter LLP, which he joined in 2008. He has received, and continues to receive, no compensation from Goodwin Procter LLP since joining as counsel. The Company retains Goodwin Procter LLP as legal counsel for various matters, primarily consisting of intellectual property matters. There was no payment to Goodwin Procter LLP during the year ended December 31, 2017. During the year ended December 31, 2016, the Company’s payment to Goodwin Procter LLP was immaterial. During the year ended December 31, 2015, the Company made payments to Goodwin Procter LLP of $0.4 million. There was no accrued liability due to Goodwin Procter LLP in the consolidated balance sheet as of December 31, 2017 or 2016.

Segment and Geographic Information

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Segment and Geographic Information

14.	Segment and Geographic Information

The Company has determined that the chief executive officer is the chief operating decision maker (“CODM”). The CODM reviews financial information presented for the Company’s various clinical trial programs as well as results on a consolidated basis. License, milestone and collaboration services revenues received are not allocated to various programs for purposes of determining a profit measure and resource allocation decisions are made by the CODM based primarily on consolidated results. As such, the Company has concluded that it operates as one segment. Supplemental enterprise-wide information has been presented below.

Geographic Revenues

Geographic revenues, which are based on the bill to region, are as follows (in thousands):

	Years Ended December 31,
	2017		2016		2015
Europe	$	108,759	$	153,669	$	159,123
Japan (related party)		16,885		25,778		21,596
All other		24		130		109
Total revenue	$	125,668	$	179,577	$	180,828

Geographic Long-Lived Assets

Property and equipment, net by geographic location are as follows (in thousands):

	December 31,
	2017		2016
United States	$	107,228	$	109,886
China		22,248		13,771
Total property and equipment	$	129,476	$	123,657

Customer Concentration

Substantially all of the Company’s revenues to date have been generated from the following collaboration partners that respectively accounted for more than 10% of the Company’s total revenue and accounts receivable:

	Percentage of Revenue									Percentage of Accounts Receivable
	Years Ended December 31,									December 31,
	2017			2016			2015			2017			2016
Astellas—Related party		13	%		14	%		12	%		47	%		39	%
AstraZeneca		87	%		86	%		88	%		53	%		61	%

Schedule II - Valuation and Qualifying Accounts

12 Months Ended

Dec. 31, 2017

Valuation And Qualifying Accounts [Abstract]

Schedule II - Valuation and Qualifying Accounts

Schedule II: Valuation and Qualifying Accounts

(in thousands)

			Charged		Charged
	Balance at		(Credited)		to Other
	Beginning of		to Statement		Accounts -		Deductions,		Balance at
	Year		of Operation		Equity		Net		End of Year
Valuation allowances for deferred tax assets
Year ended December 31, 2017	$	128,995	$	11,039	$	19,506	$	—	$	159,540
Year ended December 31, 2016	$	116,718	$	12,277	$	—	$	—	$	128,995
Year ended December 31, 2015	$	94,731	$	21,987	$	—	$	—	$	116,718

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Presentation

The Company operates in one segment — the discovery, development and commercialization of novel therapeutics to treat serious unmet medical needs.

Foreign Currency Translation

Use of Estimates

Concentration of Credit Risk and Other Risks and Uncertainties

	December 31,
	2017			2016
Astellas Pharma Inc. (“Astellas”)—Related party		47	%		39	%
AstraZeneca AB (“AstraZeneca”)		53	%		61	%

Cash, Cash Equivalents and Restricted Time Deposits

Investments

Fair Value of Financial Instruments

Property and Equipment

Impairment of Long-Lived Assets

Revenue Recognition

Substantially all of the Company’s revenues to date have been generated from its collaboration agreements.

•	provides guidance on how deliverables in an arrangement should be separated and how the arrangement consideration should be allocated to the separate units of accounting;

•	requires an entity to determine the selling price of a separate deliverable using a hierarchy of (i) vendor-specific objective evidence (“VSOE”), (ii) third-party evidence (“TPE”), or (iii) best estimate of selling price (“BESP”); and

•	requires the allocation of the arrangement consideration, at the inception of the arrangement, to the separate units of accounting based on relative selling price.

Research and Development Expenses

Clinical Trial Accruals

General and Administrative Expenses

Income Taxes

The Company includes interest and penalties related to unrecognized tax benefits within income tax expense in the Consolidated Statements of Operations.

Stock-Based Compensation

The fair value of employee stock options was estimated using the following assumptions:

Expected Dividend Yield. The Company has never declared or paid any cash dividends and does not plan to pay cash dividends in the foreseeable future.

Comprehensive Income (Loss)

Recently Issued and Adopted Accounting Guidance

Recently Issued Accounting Guidance Not Yet Adopted

Collaboration Arrangements

Accounting for the Astellas Agreements

For each of the Astellas agreements, the Company has evaluated the deliverables within the respective arrangements and has separated them into various units of accounting.

The units of accounting that were analyzed, along with their general timing of delivery or performance of service and general timing of revenue recognition, are as follows:

•

•	Committee service. This deliverable is satisfied and revenue is recognized throughout the course of the various agreements as meetings are attended.

Accounting for the AstraZeneca Agreements

U.S./RoW Agreement:

The units of accounting that were analyzed, along with their general timing of delivery or performance of service and general timing of revenue recognition, are as follows:

•

Manufacturing of clinical supplies of products. This deliverable is satisfied as supplies for clinical product are delivered for use in the Company’s clinical trial programs during the development period, or pre-commercialization period. Revenue is recognized based on the estimated proportion of the development services performed during the development period. These estimates are made at the beginning of each accounting period and will likely change throughout the course of the agreements. As new information related to these estimates becomes available, the Company may adjust the timing of revenue recognition related to this unit of accounting.

•

•	Committee service. This deliverable is satisfied and revenue is recognized throughout the course of the various agreements as meetings are attended.

China Agreement:

The units of accounting that were analyzed, along with their general timing of delivery or performance of service and general timing of revenue recognition, are as follows:

•

Other Revenues

Other revenues consist primarily of collagen material sold for research purposes. Other revenues were immaterial for each of the three years ended December 31, 2017.

Deferred Revenue

Fair Value Measurements

Level 1: Quoted prices in active markets for identical assets or liabilities.

Level 2: Observable inputs other than quoted prices in active markets for identical assets or liabilities.

Level 3: Unobservable inputs.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of Significant Balance of Accounts Receivable

The Company has not experienced any loss on its deposits of cash and cash equivalents. Included in current assets are significant balances of accounts receivable as follows:

	December 31,
	2017			2016
Astellas Pharma Inc. (“Astellas”)—Related party		47	%		39	%
AstraZeneca AB (“AstraZeneca”)		53	%		61	%

Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2017

Japan [Member]

Summary of Revenue Recognized under Agreement

Amounts recognized as revenue under the Japan Agreement are shown below (in thousands):

		Years Ended December 31,
Agreement	Deliverable	2017		2016		2015
Japan	License	$	1,310	$	3,465	$	1,024
	Milestones		—		10,000		—
	Total license and milestone revenue	$	1,310	$	13,465	$	1,024
	Collaboration services revenue*	$	64	$	166	$	198

Total Arrangement Consideration Allocated to Deliverables along with Associated Deferred Revenue

The total arrangement consideration has been allocated to each of the following deliverables under the Japan Agreement, along with any associated deferred revenue as follows (in thousands):

	Cumulative Revenue Through December 31, 2017		Deferred Revenue at December 31, 2017		Total Consideration Through December 31, 2017
License	$	47,020	$	—	$	47,020
When and if available compounds		25		24		49
Manufacturing--clinical supplies		2,180		—		2,180
Committee services		21		—		21
Total license and collaboration services revenue	$	49,246	$	24	$	49,270

Europe [Member]

Summary of Revenue Recognized under Agreement

Amounts recognized as revenue under the Europe Agreement were as follows (in thousands):

		Years Ended December 31,
Agreement	Deliverable	2017		2016		2015
Europe	License	$	13,997	$	10,956	$	17,677
	Milestones		—		—		—
	Total license and milestone revenue	$	13,997	$	10,956	$	17,677
	Collaboration services revenue*	$	1,514	$	1,191	$	2,697

Total Arrangement Consideration Allocated to Deliverables along with Associated Deferred Revenue

The total arrangement consideration has been allocated to each of the following deliverables under the Europe Agreement, along with any associated deferred revenue as follows (in thousands):

	Cumulative Revenue Through December 31, 2017		Deferred Revenue at December 31, 2017		Total Consideration Through December 31, 2017
License	$	426,270	$	—	$	426,270
When and if available compounds		423		388		811
Manufacturing--clinical supplies		10,210		—		10,210
Development services--in progress		34,153		—		34,153
Committee services		295		—		295
Total license and collaboration services revenue	$	471,351	$	388	$	471,739

U.S./RoW [Member]

Summary of Revenue Recognized under Agreement

Amounts recognized as revenue under the U.S./RoW and China Agreements were as follows (in thousands):

		Years Ended December 31,
Agreement	Deliverable	2017		2016		2015
U.S. / RoW and China	License	$	65,749	$	112,931	$	114,392
	Milestones		15,000		—		15,000
	Total license and milestone revenue	$	80,749	$	112,931	$	129,392
	Collaboration services revenue*	$	28,010	$	40,738	$	29,731
	China single unit of accounting**	$	—	$	—	$	—

Total Arrangement Consideration Allocated to Deliverables along with Associated Deferred Revenue

	Cumulative Revenue Through December 31, 2017		Deferred Revenue at December 31, 2017		Total Consideration Through December 31, 2017
License	$	468,446	$	—	$	468,446
Co-development, information sharing & committee services		118,679		23,744		142,423
Manufacturing--clinical supplies		463		24		487
China-single unit of accounting		—		96,019		96,019
Total license and collaboration services revenue	$	587,588	$	119,787	$	707,375

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Values of Financial Assets Measured on Recurring Basis

The fair values of the Company’s financial assets that are measured on a recurring basis are as follows (in thousands):

	December 31, 2017
	Level 1		Level 2		Level 3		Total
Corporate bonds	$	—	$	53,943	$	—	$	53,943
Bond and mutual funds		18,402		—		—		18,402
Equity investments		221		—		—		221
Money market funds		569,942		—		—		569,942
Total	$	588,565	$	53,943	$	—	$	642,508

	December 31, 2016
	Level 1		Level 2		Level 3		Total
Corporate bonds	$	—	$	126,683	$	—	$	126,683
Bond and mutual funds		22,462		—		—		22,462
Equity investments		225		—		—		225
Money market funds		94,543		—		—		94,543
Certificate of deposits		—		1,037		—		1,037
Total	$	117,230	$	127,720	$	—	$	244,950

Fair Values of Financial Liabilities Carried at Historical Cost

The fair values of the Company’s financial liabilities that are carried at historical cost are as follows (in thousands):

	December 31, 2017
	Level 1		Level 2		Level 3		Total
Lease financing obligations	$	—	$	—	$	98,476	$	98,476

	December 31, 2016
	Level 1		Level 2		Level 3		Total
Lease financing obligations	$	—	$	—	$	97,856	$	97,856

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Cash and Cash Equivalents

Cash and cash equivalents consisted of the following (in thousands):

	December 31,
	2017		2016
Cash	$	103,716	$	79,239
Money market funds		569,942		94,543
Total cash and cash equivalents	$	673,658	$	173,782

Schedule of Property and Equipment

Property and equipment consisted of the following (in thousands):

	December 31,
	2017			2016
Laboratory equipment	$	19,497		$	18,533
Computer equipment		6,006			5,678
Furniture and fixtures		5,575			5,533
Leasehold improvements		93,758			93,564
Building shell (Refer to Note 8)		53,879			53,879
Construction in progress		10,402			109
Total property and equipment	$	189,117		$	177,296
Less: accumulated depreciation		(59,641	)		(53,639	)
Property and equipment, net	$	129,476		$	123,657

Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Available-for-Sale Investments

	December 31, 2017
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Corporate bonds	$	53,985	$	4	$	(46	)	$	53,943
Bond and mutual funds		17,249		1,153		—			18,402
Equity investments		126		95		—			221
Total investments	$	71,360	$	1,252	$	(46	)	$	72,566

	December 31, 2016
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Corporate bonds	$	126,550	$	182	$	(49	)	$	126,683
Certificate of deposits		1,037		—		—			1,037
Bond and mutual funds		22,305		157		—			22,462
Equity investments		125		100		—			225
Total investments	$	150,017	$	439	$	(49	)	$	150,407

Summary of Contractual Maturities Available-for-Sale Investments at Fair Value

The contractual maturities of available-for-sale investments were as follows (in thousands):

	December 31, 2017
Within one year	$	53,943
After one year through four years		—
Total debt investments		53,943
Bond and mutual funds		18,402
Equity investments		221
Total investments	$	72,566

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31,
	2017		2016
Preclinical and clinical trial accruals	$	32,321	$	29,550
Payroll and related accruals		18,810		14,232
Property taxes and other		4,201		451
Professional services		1,991		1,252
Other		6,458		5,429
Total accrued liabilities	$	63,781	$	50,914

Commitment and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments Under all Non-Cancelable Operating Lease Obligations

Future minimum lease payments under all non-cancelable operating lease obligations as of December 31, 2017 are as follows (in thousands):

Year Ending	Operating Leases
2018	$	445
2019		310
2020		155
2021		25
2022		16
Total minimum payments	$	951

Schedule of Future Minimum Lease Payments on Consolidated Basis Under Company's Facility Financing Lease Obligations

Future minimum lease payments, on a consolidated basis, under the Company’s facility lease financing obligations as of December 31, 2017 are as follows (in thousands):

Year Ending	Lease financing obligations
2018	$	14,250
2019		14,466
2020		14,687
2021		14,171
2022		14,335
Thereafter		12,873
Total minimum payments	$	84,782

Equity and Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Common Stock Reserved for Future Issuance

	December 31,
	2017		2016
Common stock outstanding		82,498		63,665
Stock options outstanding		11,550		13,660
RSUs outstanding		1,562		1,211
Common stock warrants outstanding		4		4
Shares reserved for future stock options and RSUs grant		4,190		4,032
Shares reserved for future ESPP offering		2,024		1,638
Total shares of common stock reserved		101,828		84,210

Summary of Stock Option Transactions

Stock option transactions, including forfeited options granted under the 2014 Plan as well as prior plans, are summarized below:

	Shares (In thousands)			Weighted Average Exercise per Share		Weighted Average Remaining Contractual Life (In Years)		Aggregate Intrinsic Value (In thousands)
Outstanding at December 31, 2016		13,660		$	11.35
Granted		1,923			26.95
Exercised		(3,827	)		8.10
Expired		(34	)		24.58
Forfeited		(172	)		22.05
Outstanding at December 31, 2017		11,550			14.82		5.80	$	376,670
Vested and expected to vest, December 31, 2017		11,550			14.82		5.80		376,670
Exercisable at December 31, 2017		8,319		$	10.98		4.71	$	303,049

Summary of RSU Activity

The following table summarizes RSU activity:

	Shares (In thousands)			Fair Value at Grant
Unvested at December 31, 2016		1,211		$	21.60
Granted		978			26.59
Vested		(563	)		21.34
Forfeited		(64	)		23.34
Unvested at December 31, 2017		1,562		$	24.75

Schedule of Allocated Stock-Based Compensation Expense

Stock-based compensation expense allocated to research and development and general and administrative expense for the years ended December 31, 2017, 2016, and 2015 was as follows (in thousands):

	Years Ended December 31,
	2017		2016		2015
Research and development	$	21,807	$	19,070	$	16,987
General and administrative		15,732		13,062		10,694
Total stock-based compensation expense	$	37,539	$	32,132	$	27,681

Schedule of Assumptions used to Estimate Fair Value of Stock Options Granted and Employee Stock Purchase Plans

The assumptions used to estimate the fair value of stock options granted and ESPPs using the Black-Scholes option valuation model were as follows:

	Years Ended December 31,
	2017			2016			2015
Stock Options
Expected term (in years)		5.7			5.3			5.2
Expected volatility		71.5	%		69.9	%		69.9	%
Risk-free interest rate		2.2	%		1.4	%		1.7	%
Expected dividend yield		—			—			—
Weighted average estimated fair value	$	16.96		$	11.49		$	16.12

ESPPs
Expected term (in years)	0.5 - 2.0			0.5 - 2.0			0.4 - 2.0
Expected volatility	52.8 - 77.2		%	61.9 - 80.7		%	58.5 - 69.0		%
Risk-free interest rate	0.5 - 1.6		%	0.2 - 1.0		%	0.1 - 0.6		%
Expected dividend yield		—			—			—
Weighted average estimated fair value	$	9.41		$	9.94		$	13.03

Schedule of Warrants to Purchase Shares of Common Stock

The following warrants to purchase shares of Common Stock were issued in connection with certain facility and equipment lease financing arrangements and are outstanding at December 31, 2017:

Year of Issuance	Number of Shares		Exercise Price per Share		Reason for Issuance	Expiration Date
2000		4,430	$	15.00	Issued in connection with lease agreement	Five years after initial public offering or upon merger or sale of the Company’s assets, whichever occurs first
		4,430

- Definition

Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable.

+ References + Details

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Schedule of Anti-dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share

The following securities were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive for the three years presented (in thousands):

	Years Ended December 31,
	2017		2016		2015
Employee stock options		11,550		13,660		13,583
RSUs outstanding		1,562		1,211		865
Warrants		4		4		7
		13,116		14,875		14,455

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Components of Loss Before Income Taxes

The components of loss before income taxes are as follows (in thousands):

	Years Ended December 31,
	2017			2016			2015
Domestic	$	(101,234	)	$	(38,156	)	$	(66,411	)
Foreign		(24,648	)		(23,595	)		(19,126	)
Loss before provision for income taxes	$	(125,882	)	$	(61,751	)	$	(85,537	)

Schedule of Components of Provision For (Benefit From) Income Taxes

The provision for (benefit from) income taxes consists of the following (in thousands):

	Years Ended December 31,
	2017		2016			2015
Current:
Federal	$	—	$	—		$	—
State		2		2			2
Foreign		319		139			240
Total current	$	321	$	141		$	242
Deferred:
Federal	$	—	$	(212	)	$	—
State		—		—			—
Foreign		—		—			—
Total deferred	$	—	$	(212	)	$	—
Total provision for (benefit from) income taxes	$	321	$	(71	)	$	242

Schedule of Reconciliation Between Statutory Federal Income Tax Rate and Effective Tax Rate

The following is the reconciliation between the statutory federal income tax rate and the Company’s effective tax rate:

	Years Ended December 31,
	2017			2016			2015
Tax at statutory federal rate		34.0	%		34.0	%		34.0	%
State tax		—	%		—	%		—	%
Stock-based compensation expense		18.5	%		(7.9	)%		(4.6	)%
Change in deferred tax assets due to rate change		43.9	%		—	%		—	%
Change in valuation allowance due to rate change		(43.9	)%		—	%		—	%
Net operating losses not benefitted		(43.8	)%		(12.9	)%		(21.7	)%
Foreign net operating losses benefitted		(6.7	)%		(13.0	)%		(7.6	)%
Orphan drug credit		(2.0	)%		—	%		—	%
Other		(0.3	)%		(0.1	)%		(0.4	)%
Total		(0.3	)%		0.1	%		(0.3	)%

Schedule of Significant Components of Deferred Tax Assets

Significant components of the Company’s deferred tax assets are as follows (in thousands):

	December 31,
	2017			2016
Federal and state net operating loss carryforwards	$	71,256		$	42,900
Tax credit carryforwards		39,488			29,846
Foreign net operating loss carryforwards		15,052			11,704
Stock-based compensation		7,835			11,231
Lease obligations		2,737			4,414
Reserves and accruals		4,851			5,465
Deferred revenue		18,103			22,909
Other		420			741
Subtotal		159,742			129,210
Less: Valuation allowance		(159,540	)		(128,995	)
Net deferred tax assets		202			215

Fixed assets		(181	)		(122	)
Other		(21	)		(93	)
Net deferred tax liabilities		(202	)		(215	)
Total net deferred tax assets	$	—		$	—

Schedule of Reconciliation of the Beginning and Ending Amounts of Unrecognized Income Tax Benefits

A reconciliation of the beginning and ending amounts of unrecognized income tax benefits during the three years ended December 31, 2017 is as follows (in thousands):

	Federal and State
Balance as of December 31, 2014	$	19,122
Decrease due to prior positions		(2,382	)
Increase due to current year position		7,473
Balance as of December 31, 2015		24,213
Decrease due to prior positions		(7,109	)
Increase due to current year position		2,550
Balance as of December 31, 2016		19,654
Increase due to prior positions		303
Increase due to current year position		5,448
Decrease due to U.S. tax rate change		(2,044	)
Balance as of December 31, 2017	$	23,361

Segment and Geographic Information (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Schedule of Revenue by Geographic Area

Geographic revenues, which are based on the bill to region, are as follows (in thousands):

	Years Ended December 31,
	2017		2016		2015
Europe	$	108,759	$	153,669	$	159,123
Japan (related party)		16,885		25,778		21,596
All other		24		130		109
Total revenue	$	125,668	$	179,577	$	180,828

Schedule of Long Lived Assets by Geographic Area

Property and equipment, net by geographic location are as follows (in thousands):

	December 31,
	2017		2016
United States	$	107,228	$	109,886
China		22,248		13,771
Total property and equipment	$	129,476	$	123,657

Schedule of Customer Concentration by Collaboration Partners

	Percentage of Revenue									Percentage of Accounts Receivable
	Years Ended December 31,									December 31,
	2017			2016			2015			2017			2016
Astellas—Related party		13	%		14	%		12	%		47	%		39	%
AstraZeneca		87	%		86	%		88	%		53	%		61	%

The Company - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Aug. 24, 2017	Apr. 11, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Description [Line Items]
Net proceeds from offering			$ 34,910	$ 9,881	$ 14,992
Follow On Offering
Business Description [Line Items]
Common stock shares sold	9,200,000	5,228,750
Public offering price	$ 40.75	$ 22.95
Net proceeds from offering	$ 356,200	$ 115,100
Underwriting discounts and commissions	18,700	4,900
Offering expenses	$ 400	$ 600

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jan. 01, 2015 USD ($)
Accounting Policy [Line Items]
Number of operating segment \| Segment	1
Highly liquid investment maturity period	three months or less
Restricted time deposits	$ 5,181,000	$ 6,217,000
Cash and cash equivalents	$ 673,658,000	173,782,000	$ 153,324,000	$ 165,455,000
Long term Investments Maturity	12 months
Short term investments Maturity	12 months
Impairment of long-lived assets	$ 0
Increase in valuation allowance	30,500,000	12,300,000		$ 22,000,000
New Revenue Standards [Member] \| Revenue [Member]
Accounting Policy [Line Items]
Increase (reduction) in revenue	5,300,000	$ 3,600,000	$ (8,400,000)
ASU 2016-09 [Member]
Accounting Policy [Line Items]
Retrospective increase in deferred tax assets for previously unrecognized excess tax benefits	19,500,000
Increase in valuation allowance	19,500,000
Net impact to accumulated deficit	$ 0
ASU 2014-09 [Member] \| Accumulated Deficit [Member]
Accounting Policy [Line Items]
Increase in accumulative deficit					$ 35,200,000
Minimum [Member] \| Computer Equipment [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life	3 years
Minimum [Member] \| Laboratory Equipment [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life	3 years
Minimum [Member] \| Furniture and Fixtures [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life	3 years
Maximum [Member] \| Computer Equipment [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life	5 years
Maximum [Member] \| Laboratory Equipment [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life	5 years
Maximum [Member] \| Furniture and Fixtures [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life	5 years
Foreign subsidiaries [Member]
Accounting Policy [Line Items]
Cash and cash equivalents	$ 32,300,000

Summary of Significant Accounting Policies - Schedule of Significant Balance of Accounts Receivable (Detail) - Accounts Receivable [Member] - Credit Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Astellas Agreement [Member]
Accounting Policy [Line Items]
Concentration risk, percentage	47.00%	39.00%
AstraZeneca Agreements [Member]
Accounting Policy [Line Items]
Concentration risk, percentage	53.00%	61.00%

Collaboration Agreements - Astellas Agreements - Additional Information (Detail) - Astellas Agreement [Member] - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended						35 Months Ended	45 Months Ended
	Apr. 30, 2006	Jun. 30, 2005	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010	Feb. 28, 2009	Feb. 28, 2009
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received											$ 360,100
Japan [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received											$ 40,100
Development and regulatory approval milestones		$ 117,500
Commercial sales milestone		$ 15,000
Additional consideration based on net sales description				Low 20% range
Clinical development milestones							$ 12,500
Milestones revenue			$ 10,000	$ 0	$ 10,000	$ 0
Europe [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received										$ 320,000
Development and regulatory approval milestones	$ 425,000
Additional consideration based on net sales description				Low 20% range
Clinical development milestones								$ 50,000	$ 40,000
Milestones revenue				$ 0	$ 0	$ 0
Percentage of joint development costs committed to fund	50.00%

Collaboration Agreements - AstraZeneca Agreements - Additional Information 1 (Detail) - AstraZeneca Agreements [Member] - USD ($) $ in Thousands		3 Months Ended				12 Months Ended
	Jul. 30, 2013	Dec. 31, 2017	Sep. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S./RoW [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected upfront, non-contingent and time-based payments	$ 374,000
Development and regulatory approval milestones	550,000
Commercial sales milestone	325,000
Shared development costs				$ 233,000
Additional consideration based on net sales description						Low 20% range
Contingent payment	62,000
Milestone payment, revenue recognition						$ 15,000	$ 0	$ 15,000
U.S./RoW [Member] \| FibroGen, Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Shared development costs				$ 116,500
U.S./RoW [Member] \| Development Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receipt of development milestone payment					$ 15,000
China [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development and regulatory approval milestones	161,000
Commercial sales milestone	167,500
Proceeds from upfront payments	28,200
Contingent payment	$ 20,000
Estimated joint development service period			2018
Estimated joint development extended service period			2020
Milestone payment, revenue recognition		$ 15,000

Collaboration Agreements - Accounting for the Astellas Agreements - Additional Information 2 (Detail) - Astellas Agreement [Member] - USD ($) $ in Millions	1 Months Ended		12 Months Ended	35 Months Ended	45 Months Ended	141 Months Ended
	Apr. 30, 2006	Jun. 30, 2005	Dec. 31, 2017	Feb. 28, 2009	Feb. 28, 2009	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received					$ 360.1
Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Discount rate applied			17.50%
Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Discount rate applied			20.00%
Europe [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received				$ 320.0
Development costs						$ 151.7
Non-contingent performance period	36 months
Total potential milestones	$ 425.0
Europe [Member] \| Clinical and Development Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones	90.0
Europe [Member] \| Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones	335.0
Europe [Member] \| Marketing approval milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones	$ 25.0
Japan [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received					$ 40.1
Total potential milestones		$ 132.5
Commercial sales milestone		15.0
Japan [Member] \| Clinical and Development Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones		22.5
Japan [Member] \| Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones		$ 95.0

Collaboration Agreements - Accounting for the AstraZeneca Agreements - Additional Information 3 (Detail) - AstraZeneca Agreements [Member] - USD ($) $ in Millions			9 Months Ended	12 Months Ended	36 Months Ended
	Dec. 31, 2013	Jul. 30, 2013	Mar. 31, 2014	Dec. 31, 2017	Jun. 30, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate against projected net revenues				40.00%
Discount rate applied				17.50%
U.S./RoW [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-contingent performance period		89 months
Upfront, non-contingent and time-based payments received		$ 82.0			$ 374.0
Remaining up-front, non-contingent and time-based payments		292.0
Upfront, non-contingent and time-based payments with extended payment terms		230.0
Contingent payment		62.0
Total potential milestones		875.0
Non-substantive milestones		160.0
Commercial sales milestone		325.0
U.S./RoW [Member] \| Clinical and Development Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones		65.0
U.S./RoW [Member] \| Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones		325.0
China [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received	$ 16.2
Upfront, non-contingent and time-based payments with extended payment terms		12.0
Contingent payment		20.0
Total potential milestones		348.5
Commercial sales milestone		167.5
Proceeds from upfront payments		28.2
Upfront payments received			$ 12.0
Commercial sales and other events milestone		187.5
China [Member] \| Clinical and Development Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones		15.0
China [Member] \| Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Substantive milestones		$ 146.0

Collaboration Agreements - Summary of Revenue Recognized under Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total license and milestone revenue		$ 96,056	$ 137,352	$ 148,093
Collaboration services revenue		29,612	42,225	32,735
Revenue recognized		125,668	179,577	180,828
Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Revenue recognized		108,759	153,669	159,123
Astellas Agreement [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total license and milestone revenue		15,307	24,421	18,701
Collaboration services revenue		1,578	1,357	2,895
Astellas Agreement [Member] \| Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
License revenue		1,310	3,465	1,024
Milestones revenue	$ 10,000	0	10,000	0
Total license and milestone revenue		1,310	13,465	1,024
Collaboration services revenue		64	166	198
Astellas Agreement [Member] \| Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
License revenue		13,997	10,956	17,677
Milestones revenue		0	0	0
Total license and milestone revenue		13,997	10,956	17,677
Collaboration services revenue		1,514	1,191	2,697
AstraZeneca Agreements [Member] \| China-single unit of accounting [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Revenue recognized		0	0	0
AstraZeneca Agreements [Member] \| U.S./RoW [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
License revenue		65,749	112,931	114,392
Milestones revenue		15,000	0	15,000
Total license and milestone revenue		80,749	112,931	129,392
Collaboration services revenue		$ 28,010	$ 40,738	$ 29,731

Collaboration Agreements - Total Arrangement Consideration Allocated to Deliverables along with Associated Deferred Revenue (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Astellas Agreement [Member] \| Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	$ 49,246
Deferred Revenue	24
Total Consideration	49,270
Astellas Agreement [Member] \| Japan [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	47,020
Deferred Revenue	0
Total Consideration	47,020
Astellas Agreement [Member] \| Japan [Member] \| When and if available compounds [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	25
Deferred Revenue	24
Total Consideration	49
Astellas Agreement [Member] \| Japan [Member] \| Manufacturing-clinical supplies [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	2,180
Deferred Revenue	0
Total Consideration	2,180
Astellas Agreement [Member] \| Japan [Member] \| Committee services [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	21
Deferred Revenue	0
Total Consideration	21
Astellas Agreement [Member] \| Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	471,351
Deferred Revenue	388
Total Consideration	471,739
Astellas Agreement [Member] \| Europe [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	426,270
Deferred Revenue	0
Total Consideration	426,270
Astellas Agreement [Member] \| Europe [Member] \| When and if available compounds [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	423
Deferred Revenue	388
Total Consideration	811
Astellas Agreement [Member] \| Europe [Member] \| Manufacturing-clinical supplies [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	10,210
Deferred Revenue	0
Total Consideration	10,210
Astellas Agreement [Member] \| Europe [Member] \| Committee services [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	295
Deferred Revenue	0
Total Consideration	295
Astellas Agreement [Member] \| Europe [Member] \| Development services-in progress [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	34,153
Deferred Revenue	0
Total Consideration	34,153
AstraZeneca Agreements [Member] \| U.S./RoW [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	587,588
Deferred Revenue	119,787
Total Consideration	707,375
AstraZeneca Agreements [Member] \| U.S./RoW [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	468,446
Deferred Revenue	0
Total Consideration	468,446
AstraZeneca Agreements [Member] \| U.S./RoW [Member] \| Manufacturing-clinical supplies [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	463
Deferred Revenue	24
Total Consideration	487
AstraZeneca Agreements [Member] \| U.S./RoW [Member] \| Co-development, information sharing & committee services [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	118,679
Deferred Revenue	23,744
Total Consideration	142,423
AstraZeneca Agreements [Member] \| U.S./RoW [Member] \| China-single unit of accounting [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	0
Deferred Revenue	96,019
Total Consideration	$ 96,019

Fair Value Measurements - Fair Values of Financial Liabilities Carried at Historical Cost (Detail) - Lease financing obligations [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value disclosure	$ 98,476	$ 97,856
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value disclosure	0	0
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value disclosure	0	0
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value disclosure	$ 98,476	$ 97,856

Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Transfers of assets from level 1 to 2	$ 0	$ 0	$ 0
Transfers of assets from level 2 to 1	0	0	0
Transfers of liabilities from level 1 to 2	0	0	0
Transfers of liabilities from level 2 to 1	0	0	0
Transfers of assets into level 3	0	0	0
Transfers of assets out of level 3	0	0	0
Transfers of liabilities into level 3	0	0	0
Transfers of liabilities out of level 3	$ 0	$ 0	$ 0

Balance Sheet Components - Schedule of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash And Cash Equivalents [Abstract]
Cash	$ 103,716	$ 79,239
Money market funds	569,942	94,543
Total cash and cash equivalents	$ 673,658	$ 173,782	$ 153,324	$ 165,455

Balance Sheet Components - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 189,117	$ 177,296
Less: accumulated depreciation	(59,641)	(53,639)
Property and equipment, net	129,476	123,657
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	19,497	18,533
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	6,006	5,678
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	5,575	5,533
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	93,758	93,564
Building shell [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	53,879	53,879
Construction in progress [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 10,402	$ 109

Balance Sheet Components - Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Available-for-Sale Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 71,360	$ 150,017
Gross Unrealized Holding Gains	1,252	439
Gross Unrealized Holding Losses	(46)	(49)
Fair Value	72,566	150,407
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53,985	126,550
Gross Unrealized Holding Gains	4	182
Gross Unrealized Holding Losses	(46)	(49)
Fair Value	53,943	126,683
Certificate of deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,037
Gross Unrealized Holding Gains		0
Gross Unrealized Holding Losses		0
Fair Value		1,037
Bond and mutual funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,249	22,305
Gross Unrealized Holding Gains	1,153	157
Gross Unrealized Holding Losses	0	0
Fair Value	18,402	22,462
Equity investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	126	125
Gross Unrealized Holding Gains	95	100
Gross Unrealized Holding Losses	0	0
Fair Value	$ 221	$ 225

Balance Sheet Components - Summary of Contractual Maturities Available-for-Sale Investments at Fair Value(Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments Schedule [Abstract]
Within one year	$ 53,943
After one year through four years	0
Total debt investments	53,943
Bond and mutual funds	18,402
Equity investments	221
Total investments	$ 72,566	$ 150,407

Balance Sheet Components - Schedule of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities Current [Abstract]
Preclinical and clinical trial accruals	$ 32,321	$ 29,550
Payroll and related accruals	18,810	14,232
Property taxes and other	4,201	451
Professional services	1,991	1,252
Other	6,458	5,429
Total accrued liabilities	$ 63,781	$ 50,914

Product Development Obligations - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) DevelopmentObligation	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Number of product development obligations \| DevelopmentObligation	11
Accrued product development costs excluding interest	$ 11.3	$ 9.9
Accrued Interest	$ 5.9	$ 4.9
Bank of Finland Interest Rate [Member]
Debt Instrument [Line Items]
Percentage points deducted to reference rate to compute effective interest rate	1.00%
Minimum [Member]
Debt Instrument [Line Items]
Interest rate on product development advances	3.00%

Convertible Note Payable - Additional Information (Detail) - FibroGen China [Member] - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2013	Dec. 31, 2017
Debt Instrument [Line Items]
Convertible promissory note	$ 0.6
Interest rate of convertible promissory note	2.00%
Anniversary date of promissory note		8 years

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under all Non-Cancelable Operating Lease Obligations (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 445
2019	310
2020	155
2021	25
2022	16
Total minimum payments	$ 951

Commitment and Contingencies - Additional Information (Detail) $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Feb. 28, 2013 USD ($) ft²	Sep. 30, 2006 USD ($) ft² $ / ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2012 USD ($)
Commitments And Contingencies [Line Items]
Restricted time deposits			$ 5,181	$ 6,217	$ 5,181	$ 6,217
FibroGen, Inc. [Member]
Commitments And Contingencies [Line Items]
Land subject to leases \| ft²		234,249
Initial term of lease contract		15 years
Restricted time deposits		$ 7,300
Percentage of letter of credit released				0.125%
Description of lessee leasing arrangements, operating leases					The agreement included an expansion option to occupy part of an adjacent building within 31 months of the lease commencement date of November 20, 2008.
Lease incentive receivable from land lord through expansion option not used								$ 5,000
Percentage of construction costs for tenant improvement		60.00%
Tenant improvement price per square foot of rental space \| $ / ft²		140.50
Tenant improvements allowance of rental space		$ 32,500
Cost of construction capitalized		50,800
Reimbursements from landlord for tenant improvements		$ 32,500
FibroGen, Inc. [Member] \| South San Francisco [Member]
Commitments And Contingencies [Line Items]
Land subject to sublease \| ft²		106,000
Lease and sublease termination date		Feb. 28, 2015
FibroGen, Inc. [Member] \| Reclassified from Restricted Cash to Short-term Investments [Member]
Commitments And Contingencies [Line Items]
Prior period reclassification adjustment			$ 1,000	$ 1,000
FibroGen China [Member]
Commitments And Contingencies [Line Items]
Land subject to leases \| ft²	4,820
Initial term of lease contract	8 years
Percentage of construction costs for tenant improvement	100.00%
Cost of construction capitalized	$ 3,100
Reimbursements from landlord for tenant improvements	$ 500
Lease starting date	Feb. 01, 2013
Rent expenses for leased facilities					$ 3,000	2,800	$ 2,700
FibroGen China [Member] \| Research and Development Expenses and General and Administrative Expenses [Member]
Commitments And Contingencies [Line Items]
Sublease income received					$ 3,900	$ 3,800	$ 3,400

Commitment and Contingencies - Schedule of Future Minimum Lease Payments on Consolidated Basis Under Company's Facility Financing Lease Obligations (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 14,250
2019	14,466
2020	14,687
2021	14,171
2022	14,335
Thereafter	12,873
Total minimum payments	$ 84,782

Equity and Stock-based Compensation - Subsidiary Stock and Non-Controlling Interests - Additional information (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Nov. 19, 2014
Class Of Stock [Line Items]
Preferred stock, shares outstanding	0	0
IPO [Member]
Class Of Stock [Line Items]
Conversion rights, shares issued upon conversion of each preferred share			958,996
FibroGen Europe [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	42,619,022	42,619,022
Preferred stock redemption percentage	If a Preferred Share can be redeemed by a majority shareholder owning more than ninety percent (90%) of the shares of FibroGen Europe in accordance with the provisions of the Finnish Limited Liability Companies Act, the minority holders of Preferred Shares have the right to request redemption of their shares.
Minimum percentage of shareholder's approval to call for redemption of preferred shares	90.00%
Preferred stock, voting rights	one vote
Conversion rights, shares issued upon conversion of each preferred share	1
FibroGen Europe [Member] \| Series A [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	1,700,845	1,700,845
FibroGen Europe [Member] \| Series B [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	1,875,000	1,875,000
FibroGen Europe [Member] \| Series C [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	1,599,503	1,599,503
FibroGen Europe [Member] \| Series D [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	1,520,141	1,520,141
FibroGen Europe [Member] \| Series E [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	459,565	459,565
FibroGen Europe [Member] \| Series F [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	5,714,332	5,714,332
FibroGen Europe [Member] \| Series G [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	9,927,500	9,927,500
FibroGen Europe [Member] \| Series H [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	19,822,136	19,822,136
FibroGen China [Member]
Class Of Stock [Line Items]
Conversion rights, shares issued upon conversion of each preferred share	1
FibroGen China [Member] \| Series A [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	6,758,000	6,758,000
Preferred shares issued, price per share	$ 1.00
Cash dividend percentage	6.00%

Equity and Stock-based Compensation - Summary of Common Stock Reserved for Future Issuance (Detail) - shares shares in Thousands	Dec. 31, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Common stock outstanding	82,498	63,665
Stock options outstanding	11,550	13,660
RSUs outstanding	1,562	1,211
Common stock warrants outstanding	4	4
Shares reserved for future stock options and RSUs grant	4,190	4,032
Total shares of common stock reserved	101,828	84,210
ESPP [Member]
Class Of Stock [Line Items]
Shares reserved for future ESPP offering	2,024	1,638

Equity and Stock-based Compensation - Stock Plans - Additional information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total intrinsic value of options exercised		$ 303,049
RSUs released and issued net of shares withheld for taxes		326,626
Weighted-average fair value of awards granted		$ 26.59	$ 19.37	$ 29.66
2005 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of stock options		4 years
2005 Stock Plan \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration period of stock options		10 years
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of stock options		5 years
Expiration period of stock options		10 years
Termination date of equity incentive plan		Nov. 12, 2024
Option vesting term		Option vesting schedules are determined by the Company at the time of issuance and generally have a four year vesting schedule (25% vesting on the first anniversary of the vesting base date and quarterly thereafter over the next 3 years).
Number of common stock reserved for issuance		4,190,412
Common stock reserved for future issuance, Description		Shares reserved for issuance increases on January 1 of each year commencing on January 1, 2016 and ending on January 1, 2024 by the lesser of (i) the amount equal to 4% of the number of shares issued and outstanding on December 31 immediately prior to the date of increase or (ii) such lower number of shares as may be determined by the board of directors. As of December 31, 2017, the Company has reserved 4,190,412 shares of its common stock that remains unissued for issuance under the 2014 Plan.
Percentage of common stock reserved for future issuance	4.00%
Number of common stock repurchased		0	0
Total intrinsic value of options exercised		$ 111,900	$ 17,900	$ 48,700
2014 Equity Incentive Plan \| First Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of vesting rights		25.00%
2014 Equity Incentive Plan \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of fair value exercise price grant date		100.00%

Equity and Stock-based Compensation - Stock Plans - Summary of Stock Option Transactions (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding, Beginning Balance, Shares \| shares	13,660
Granted, Shares \| shares	1,923
Exercised, Shares \| shares	(3,827)
Expired, Shares \| shares	(34)
Forfeited, Shares \| shares	(172)
Outstanding, Ending Balance, Shares \| shares	11,550
Vested and expected to vest, Shares \| shares	11,550
Exercisable, Shares \| shares	8,319
Outstanding, Beginning Balance, Weighted Average Exercise per Share \| $ / shares	$ 11.35
Granted, Weighted Average Exercise per Share \| $ / shares	26.95
Exercised, Weighted Average Exercise per Share \| $ / shares	8.10
Expired, Weighted Average Exercise per Share \| $ / shares	24.58
Forfeited, Weighted Average Exercise per Share \| $ / shares	22.05
Outstanding, Ending Balance, Weighted Average Exercise per Share \| $ / shares	14.82
Vested and expected to vest, Weighted Average Exercise per Share \| $ / shares	14.82
Exercisable, Weighted Average Exercise per Share \| $ / shares	$ 10.98
Outstanding, Weighted Average Remaining Contractual Life	5 years 9 months 18 days
Vested and expected to vest, Weighted Average Remaining Contractual Life	5 years 9 months 18 days
Exercisable, Weighted Average Remaining Contractual Life	4 years 8 months 15 days
Outstanding, Aggregate Intrinsic Value \| $	$ 376,670
Vested and expected to vest, Aggregate Intrinsic Value \| $	376,670
Exercisable, Aggregate Intrinsic Value \| $	$ 303,049

Equity and Stock-based Compensation - Summary of RSU Activity (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested, Shares, Beginning Balance	1,211
Unvested, Shares, Ending Balance	1,562	1,211
Granted, Fair value at Grant	$ 26.59	$ 19.37	$ 29.66
Restricted Stock Unit [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested, Shares, Beginning Balance	1,211
Granted, Shares	978
Vested, Shares	(563)
Forfeited, Shares	(64)
Unvested, Shares, Ending Balance	1,562	1,211
Unvested, Fair value at Grant, Beginning Balance	$ 21.60
Granted, Fair value at Grant	26.59
Vested, Fair value at Grant	21.34
Forfeited, Fair value at Grant	23.34
Unvested, Fair value at Grant, Ending Balance	$ 24.75	$ 21.60

Equity and Stock-based Compensation - Employee Stock Purchase Plan - Additional information (Detail) - 2014 ESPP [Member] - shares	1 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase of common stock shares at discount	15.00%
Percentage of fair value exercise price grant date	85.00%
Number of common stock reserved for issuance	1,600,000
Common stock reserved for future issuance, Description		The Company has reserved 1,600,000 shares of its common stock for issuance under the 2014 ESPP and shares reserved for issuance increases January 1 of each year commencing January 1, 2016 by the lesser of (i) a number of shares equal to 1% of the total number of outstanding shares of common stock on December 31 immediately prior to the date of increase; (ii) 1,200,000 shares or (iii) such number of shares as may be determined by the board of directors.
Percentage of common stock reserved for future issuance	1.00%
Increase in number of shares of common stock reserved for future issuance, shares	1,200,000
Shares purchased by employees		250,834	266,720	315,385

Equity and Stock-based Compensation - Schedule of Allocated Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 37,539	$ 32,132	$ 27,681
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	21,807	19,070	16,987
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 15,732	$ 13,062	$ 10,694

Equity and Stock-based Compensation - Schedule of Assumptions used to Estimate Fair Value of Stock Options Granted and Employee Stock Purchase Plans (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 8 months 12 days	5 years 3 months 18 days	5 years 2 months 12 days
Expected volatility	71.50%	69.90%	69.90%
Risk-free interest rate	2.20%	1.40%	1.70%
Expected dividend yield	0.00%	0.00%	0.00%
Weighted average estimated fair value	$ 16.96	$ 11.49	$ 16.12
Employee stock purchase plans [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	52.80%	61.90%	58.50%
Expected volatility, maximum	77.20%	80.70%	69.00%
Risk-free interest rate, minimum	0.50%	0.20%	0.10%
Risk-free interest rate, maximum	1.60%	1.00%	0.60%
Expected dividend yield	0.00%	0.00%	0.00%
Weighted average estimated fair value	$ 9.41	$ 9.94	$ 13.03
Employee stock purchase plans [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	4 months 24 days
Employee stock purchase plans [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	2 years	2 years	2 years

Equity and Stock-based Compensation - Stock-Based Compensation - Additional information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Stock Option Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs	$ 37.6
Non-vested stock option awards granted that will be recognized on a straight-line basis over the weighted-average period	2 years 4 months 20 days
Restricted Stock Unit [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested stock option awards granted that will be recognized on a straight-line basis over the weighted-average period	2 years 8 months 12 days
Unrecognized compensation costs	$ 29.6

Equity and Stock-based Compensation - Schedule of Warrants to Purchase Shares of Common Stock (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Class Of Warrant Or Right [Line Items]
Number of Shares	4,430
Year of Issuance 2000 [Member]
Class Of Warrant Or Right [Line Items]
Year of Issuance	2000
Number of Shares	4,430
Exercise Price per Share \| $ / shares	$ 15.00
Reason for Issuance	Issued in connection with lease agreement
Expiration Date	Five years after initial public offering or upon merger or sale of the Company’s assets, whichever occurs first

Net Loss Per Share - Schedule of Anti-dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of net loss per share	13,116	14,875	14,455
Employee stock options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of net loss per share	11,550	13,660	13,583
RSUs outstanding [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of net loss per share	1,562	1,211	865
Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of net loss per share	4	4	7

Income Taxes - Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components Of Income Tax Expense Benefit Continuing Operations [Abstract]
Domestic	$ (101,234)	$ (38,156)	$ (66,411)
Foreign	(24,648)	(23,595)	(19,126)
Loss before income taxes	$ (125,882)	$ (61,751)	$ (85,537)

Income Taxes - Schedule of Components of Provision For (Benefit From) Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 0	$ 0	$ 0
State	2	2	2
Foreign	319	139	240
Total current	321	141	242
Deferred:
Federal	0	(212)	0
State	0	0	0
Foreign	0	0	0
Total deferred	0	(212)	0
Total provision for (benefit from) income taxes	$ 321	$ (71)	$ 242

Income Taxes - Schedule of Reconciliation Between Statutory Federal Income Tax Rate and Effective Tax Rate (Detail)		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Tax at statutory federal rate	35.00%	34.00%	34.00%	34.00%
State tax		0.00%	0.00%	0.00%
Stock-based compensation expense		18.50%	(7.90%)	(4.60%)
Change in deferred tax assets due to rate change		43.90%	0.00%	0.00%
Change in valuation allowance due to rate change		(43.90%)	0.00%	0.00%
Net operating losses not benefitted		(43.80%)	(12.90%)	(21.70%)
Foreign net operating losses benefitted		(6.70%)	(13.00%)	(7.60%)
Orphan drug credit		(2.00%)	0.00%	0.00%
Other		(0.30%)	(0.10%)	(0.40%)
Total		(0.30%)	0.10%	(0.30%)

Income Taxes - Schedule of Significant Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Components Of Deferred Tax Assets And Liabilities [Abstract]
Federal and state net operating loss carryforwards	$ 71,256	$ 42,900
Tax credit carryforwards	39,488	29,846
Foreign net operating loss carryforwards	15,052	11,704
Stock-based compensation	7,835	11,231
Lease obligations	2,737	4,414
Reserves and accruals	4,851	5,465
Deferred revenue	18,103	22,909
Other	420	741
Subtotal	159,742	129,210
Less: Valuation allowance	(159,540)	(128,995)
Net deferred tax assets	202	215
Fixed assets	(181)	(122)
Other	(21)	(93)
Net deferred tax liabilities	(202)	(215)
Total net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Information (Detail) - USD ($)		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Increase in valuation allowance			$ 30,500,000	$ 12,300,000		$ 22,000,000
Federal and state net operating loss carryforwards			71,256,000	42,900,000
Foreign net operating loss carryforwards			$ 15,052,000	$ 11,704,000
Tax at statutory federal rate	35.00%		34.00%	34.00%	34.00%
Reduction in deferred tax assets			$ 55,200,000
Percentage of ownership changes			0.00%
Unrecognized tax benefits			$ 23,300,000
Unrecognized tax benefits that would affect effective tax rate			400,000
Accrued interest, unrecognized tax benefits			$ 0	$ 0
Unrecognized tax benefits description			The Company does not anticipate a material change to its unrecognized tax benefits over the next twelve months that would affect the Company’s effective tax rate.
Earliest Tax Year [Member]
Income Taxes [Line Items]
Foreign statute of limitation generally remains open in the year			2008
Latest Tax Year [Member]
Income Taxes [Line Items]
Foreign statute of limitation generally remains open in the year			2017
ASU 2016-09 [Member]
Income Taxes [Line Items]
Increase in valuation allowance			$ 19,500,000
Retrospective increase in deferred tax assets for previously unrecognized excess tax benefits			19,500,000
Scenario, Forecast [Member]
Income Taxes [Line Items]
Tax at statutory federal rate		21.00%
Foreign net operating loss [Member]
Income Taxes [Line Items]
Foreign net operating loss carryforwards			$ 63,500,000
Foreign net operating loss [Member] \| Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards expiration year			2018
Foreign net operating loss [Member] \| Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards expiration year			2027
Federal [Member]
Income Taxes [Line Items]
Federal and state net operating loss carryforwards			$ 306,000,000
Operating loss carryforwards expiration year			2026
Other tax credit carryforwards			$ 38,800,000
Other tax credit carryforwards expiration year			2018
State [Member]
Income Taxes [Line Items]
Federal and state net operating loss carryforwards			$ 143,400,000
Operating loss carryforwards expiration year			2018
State [Member] \| California [Member]
Income Taxes [Line Items]
Other tax credit carryforwards			$ 22,900,000

Income Taxes - Reconciliation of the Beginning and Ending Amounts of Unrecognized Income Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Ending Balance	$ 23,300
Federal and State [Member]
Income Tax Contingency [Line Items]
Beginning balance	19,654	$ 24,213	$ 19,122
Decrease due to prior positions		(7,109)	(2,382)
Increase due to current year position	5,448	2,550	7,473
Increase due to prior positions	303
Decrease due to U.S. tax rate change	(2,044)
Ending Balance	$ 23,361	$ 19,654	$ 24,213

Related Party Transactions - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Accounts receivable from related party	$ 4,004,000	$ 4,102,000
Accrued liabilities to related party	272,000	1,615,000
Astellas [Member] \| Collaborative Arrangement [Member]
Related Party Transaction [Line Items]
Revenue related to collaboration agreements	16,900,000	25,800,000	$ 21,600,000
Expense related to collaboration agreements	1,000,000	6,400,000	9,800,000
Accounts receivable from related party	4,000,000	4,100,000
Accrued liabilities to related party	300,000	1,600,000
Goodwin Procter LLP [Member]
Related Party Transaction [Line Items]
Accrued liabilities to related party	0	$ 0
Goodwin Procter LLP [Member] \| Intellectual Property [Member]
Related Party Transaction [Line Items]
Payments for legal matters	$ 0		$ 400,000

Segment and Geographic Information - Schedule of Revenue by Geographic Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue recognized	$ 125,668	$ 179,577	$ 180,828
Europe [Member]
Segment Reporting Information [Line Items]
Revenue recognized	108,759	153,669	159,123
Japan [Member] \| Related Party [Member]
Segment Reporting Information [Line Items]
Revenue recognized	16,885	25,778	21,596
All other [Member]
Segment Reporting Information [Line Items]
Revenue recognized	$ 24	$ 130	$ 109

Segment and Geographic Information - Schedule of Long Lived Assets by Geographic Area (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment, net	$ 129,476	$ 123,657
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment, net	107,228	109,886
China [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment, net	$ 22,248	$ 13,771

Segment and Geographic Information - Schedule of Customer Concentration by Collaboration Partners (Detail) - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Percentage of Revenue [Member] \| Astellas-Related party [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	13.00%	14.00%	12.00%
Percentage of Revenue [Member] \| AstraZeneca [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	87.00%	86.00%	88.00%
Percentage of Accounts Receivable [Member] \| Astellas-Related party [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	47.00%	39.00%
Percentage of Accounts Receivable [Member] \| AstraZeneca [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	53.00%	61.00%

Schedule II - Valuation and Qualifying Accounts (Detail) - Valuation Allowances for Deferred Tax Assets [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 128,995	$ 116,718	$ 94,731
Charged (Credited) to Statement of Operation	11,039	12,277	21,987
Charged to Other Accounts - Equity	19,506	0	0
Deductions, Net	0	0	0
Balance at End of Year	$ 159,540	$ 128,995	$ 116,718

FibroGen, Inc. 401(k) Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Defined contribution plan, maximum annual contributions per employee, percent	60.00%
Defined contribution plan, employer matching contributions	$ 2.5	$ 2.3	$ 2.5

Equity and Stock-based Compensation - Common Stock - Additional information (Detail)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Common stock voting rights	one vote

Segment and Geographic Information - Additional information (Detail)	12 Months Ended
	Dec. 31, 2017 Segment
Segment Reporting [Abstract]
Number of operating segment	1