Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 31, 2015	Apr. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	FGEN
Entity Registrant Name	FIBROGEN INC
Entity Central Index Key	0000921299
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		59,268,249

Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 128,369	$ 165,455
Short-term investments	14,322	14,364
Accounts receivable ($5,278 and $5,033 from a related party)	6,963	13,453
Prepaid expenses and other current assets	5,746	4,966
Total current assets	155,400	198,238
Restricted cash	7,254	7,254
Long-term investments	139,518	144,269
Property and equipment, net	131,660	132,171
Other assets	1,708	1,596
Total assets	435,540	483,528
Current liabilities:
Accounts payable	2,433	4,551
Accrued liabilities ($4,564 and $4,594 to related parties)	42,466	48,985
Deferred revenue	9,058	9,218
Total current liabilities	53,957	62,754
Long-term portion of lease financing obligations	96,873	96,818
Product development obligations	14,774	16,465
Deferred rent	5,024	5,131
Deferred revenue, net of current	60,326	60,988
Other long-term liabilities	699	696
Total liabilities	231,653	242,852
Commitments and Contingencies
Stockholders' equity:
Preferred stock, $0.01 par value; 125,000 shares authorized at March 31, 2015 and December 31, 2014; no shares issued and outstanding at March 31, 2015 and December 31, 2014	0	0
Common stock, $0.01 par value; 225,000 shares authorized at March 31, 2015 and December 31, 2014; 59,268 and 59,046 shares issued and outstanding at March 31, 2015 and December 31, 2014	593	590
Additional paid-in capital	553,411	546,247
Accumulated other comprehensive loss	(738)	(3,149)
Accumulated deficit	(368,650)	(322,283)
Total stockholders' equity	184,616	221,405
Non-controlling interests	19,271	19,271
Total equity	203,887	240,676
Total liabilities and equity	$ 435,540	$ 483,528

Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Accounts receivable from related party	$ 5,278	$ 5,033
Accrued liabilities to related parties	$ 4,564	$ 4,594
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	59,268,000	59,046,000
Common stock, shares outstanding	59,268,000	59,046,000

Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revenue:
License and milestone revenue (includes $4,692 and $2,742 from a related party)	$ 11,506	$ 14,685
Collaboration services and other revenue (includes $634 and $750 from a related party)	4,792	3,191
Total revenue	16,298	17,876
Operating expenses:
Research and development	50,539	25,650
General and administrative	10,482	6,432
Total operating expenses	61,021	32,082
Loss from operations	(44,723)	(14,206)
Interest expense	(2,758)	(2,726)
Interest and other income, net	843	692
Loss before income taxes	(46,638)	(16,240)
Benefit from income taxes	271	0
Net loss	$ (46,367)	$ (16,240)
Net loss per basic and diluted share	$ (0.78)	$ (1.23)
Weighted average number of common shares used in net loss per basic and diluted share	59,197	13,210

Condensed Consolidated Statements of Operations (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
License and milestone revenue from a related party	$ 11,506	$ 14,685
Collaboration services and other revenue from a related party	4,792	3,191
Astellas Agreement [Member]
License and milestone revenue from a related party	4,692	2,742
Collaboration services and other revenue from a related party	$ 634	$ 750

Condensed Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (46,367)	$ (16,240)
Other comprehensive income (loss):
Foreign currency translation adjustments	1,705	10
Available-for-sale investments:
Unrealized gain (loss) on investments, net of tax effect	711	(540)
Reclassification from accumulated other comprehensive loss	(5)
Net change in unrealized gain (loss) on available-for-sale investments	706	(540)
Other comprehensive income (loss), net of taxes:	2,411	(530)
Comprehensive loss	$ (43,956)	$ (16,770)

Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating activities
Net loss	$ (46,367)	$ (16,240)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,388	912
Amortization of premium on investments	768	171
Stock-based compensation	6,446	795
Tax benefit on unrealized gain on available-for-sale securities	(271)	0
Changes in operating assets and liabilities:
Accounts receivable	6,490	(3,650)
Prepaid expenses and other current assets	(780)	(230)
Other assets	(112)	(80)
Accounts payable	(2,118)	81
Accrued liabilities	(7,048)	(726)
Deferred revenue	(822)	3,195
Lease financing liability	156	150
Other long-term liabilities	80	101
Net cash used in operating activities	(42,190)	(15,521)
Investing activities
Purchases of property and equipment	(448)	(2,331)
Proceeds from maturities of available-for-sale securities	5,000	14,546
Net cash provided by investing activities	4,552	12,215
Financing activities
Repayments of lease liability	(101)	(101)
Proceeds from issuance of common stock upon exercise of stock options	721	37
Net cash provided by (used in) financing activities	620	(64)
Effect of exchange rate change on cash and cash equivalents	(68)	(9)
Net decrease in cash and cash equivalents	(37,086)	(3,379)
Cash and cash equivalents at beginning of period	165,455	76,332
Cash and cash equivalents at end of period	$ 128,369	$ 72,953

Description of Operations and Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2015

Accounting Policies [Abstract]

Description of Operations and Summary of Significant Accounting Policies

1.	Description of Operations and Summary of Significant Accounting Policies

Description of Operations

FibroGen, Inc. (“FibroGen,” the “Company,” or “we” and other similar pronouns) was incorporated in 1993 in Delaware and is a research-based biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutics to treat serious unmet medical needs. Our focus in the areas of fibrosis and hypoxia-inducible factor (“HIF”) biology has generated multiple programs targeting various therapeutic areas. Our 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”). FG-3019 is our monoclonal antibody in Phase 2 clinical development for the treatment of idiopathic pulmonary fibrosis (“IPF”), pancreatic cancer and liver fibrosis. We have taken a global approach with respect to the development and future commercialization of our product candidates, and this includes development and commercialization in the People’s Republic of China (“China”).

On November 10, 2014, we effected a 1-for-2.5 reverse split of our common stock. Upon the effectiveness of the reverse stock split, (i) every 2.5 shares of outstanding common stock were combined into one share of common stock, (ii) the number of shares of common stock for which each outstanding option or warrant to purchase common stock is exercisable was proportionally decreased on a 1-for-2.5 basis, (iii) the exercise price of each outstanding option or warrant to purchase common stock was proportionately increased on a 1-for- 2.5 basis, (iv) the exchange ratio for each share of outstanding FibroGen Europe Oy (“FibroGen Europe”) share of stock which is exchangeable into our common stock was proportionately reduced on a 1-for-2.5 basis, and (v) the conversion ratio for each share of outstanding preferred stock which is convertible into our common stock was proportionately reduced on a 1-for-2.5 basis. All of the outstanding common stock share numbers (including shares of common stock which our outstanding preferred stock shares were convertible into), common stock warrants, share prices, exercise prices and per share amounts have been adjusted in these condensed consolidated financial statements, on a retroactive basis, to reflect this 1-for-2.5 reverse stock split for all periods presented. The par value per share and the authorized number of shares of common stock and preferred stock were not adjusted as a result of the reverse stock split.

On November 19, 2014, we closed the initial public offering of our common stock. In our initial public offering, we sold 9,315,000 shares of our common stock at a public offering price of $18.00 per share. Net proceeds from our initial public offering and concurrent private placement were $171.8 million, after deducting underwriting discounts and commissions of $11.7 million and offering expenses of $4.1 million. AstraZeneca AB (“AstraZeneca”), one of our collaboration partners, agreed to purchase from us concurrently with the closing of our initial public offering in a private placement shares of our common stock with an aggregate purchase price of $20.0 million at a price per share equal to the initial public offering price. Upon the closing of our initial public offering, all outstanding shares of our convertible preferred stock automatically converted into 33,919,954 shares of common stock. Upon the closing of our initial public offering, 958,996 shares of FibroGen Europe convertible preferred stock were converted into shares of our common stock. Our proceeds from the sale of the common stock sold in the concurrent private placement were $20.0 million.

Basis of Presentation

The condensed consolidated financial statements include the accounts of FibroGen, 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. We operate in one segment—the discovery, development and commercialization of novel therapeutics to treat serious unmet medical needs.

The condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial reporting and the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) and, therefore, do not include all information and footnote disclosures normally included in the annual consolidated financial statements. The December 31, 2014 condensed consolidated balance sheet data contained within this Form 10-Q was derived from audited consolidated financial statements included in our Form 10-K for the year ended December 31, 2014, but does not include all disclosures required by accounting principles generally accepted in the United States.

The preparation of the condensed 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. Actual results could differ from those estimates. In our opinion, the accompanying unaudited condensed consolidated financial statements include all normal recurring adjustments necessary for a fair presentation of our financial position, results of operations and cash flows for the interim periods presented.

Fair Value of Financial Instruments

We define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date.

Our valuation techniques are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect our market assumptions. We classify these inputs into the following hierarchy:

Level 1—Quoted prices for identical instruments in active markets.

Level 2—Quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations whose inputs are observable or whose significant value drivers are observable.

Level 3—Unobservable inputs and little, if any, market activity for the assets.

The 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.

Carrying amounts of certain of our financial instruments including cash equivalents, investments, receivables, accounts payable and accrued liabilities approximate fair value due to their short maturities.

Revenue Recognition

Substantially all of our revenues to date have been generated from our collaboration agreements.

Our collaboration agreements include multiple deliverables, and we, therefore, follow the guidance in Accounting Standards Codification (“ASC”) Topic 605-25, “Revenue Recognition–Multiple-Element Arrangements” (“ASC 605-25”). ASC 605-25:

•

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.

We evaluate 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, we have determined that the selling price for the deliverables within our collaboration agreements should be determined using BESP, as neither VSOE nor TPE is available. The process for determining BESP involves significant judgment on our 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, we determine 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 our 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 Topic 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 our collaboration agreements includes milestones for which we follow ASC Topic 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 our performance or on the occurrence of a specific outcome resulting from our 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 us. 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 our performance to achieve the milestone or the enhancement of the value of the item delivered as a result of a specific outcome resulting from our 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.

Net Loss per Share

Immediately prior to the initial public offering, the Company had authorized 125,000,000 shares of Preferred Stock with a par value of $0.01 per share. The Series A Preferred Stock, Series B Preferred Stock, Series C Preferred Stock, Series D Preferred Stock, Royalty Acquisition Preferred Stock and Series G-1 Preferred Stock are collectively referred to as the “Junior Preferred Stock”. The Series E Redeemable Convertible Preferred Stock and Series F Redeemable Convertible Preferred Stock are collectively referred to as the “Senior Preferred Stock”. As of December 31, 2014, there was no outstanding convertible preferred stock as all issued and outstanding preferred stock were converted to common stock at the closing of the Company’s initial public offering in November 2014.

Prior to the IPO, we applied the two-class method to calculate basic and diluted net loss per share of common stock. The two-class method is an earnings allocation method under which earnings per share is calculated for common stock considering a participating security’s rights to undistributed earnings as if all such earnings had been distributed during the period. The Junior Preferred Stock were participating securities due to their dividend rights and the Senior Preferred Stock had stated dividend rates. Our participating securities were not included in the computation of net loss per share in periods of net loss because the preferred stockholders have no contractual obligation to participate in losses.

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


	Three Months Ended March 31,
	2015		2014
Senior Preferred Stock		—		15,336
Junior Preferred Stock		—		18,584
Employee stock options		15,377		11,058
RSUs granted		1,002		—
Warrants		173		173
FibroGen Europe preferred stock		—		959

Total anti-dilutive securities		16,552		46,110

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition. This ASU 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. This ASU 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. The effective date for this ASU will be the first quarter of fiscal year 2017 using one of two retrospective application methods. In April 2015, the FASB proposed deferring the effective date by one year to the first quarter of fiscal year 2018 and proposed permitting early adoption, but not before the original effective date of the first quarter of fiscal year 2017. We are currently evaluating the impact of this guidance on our consolidated financial statements.

Collaboration Agreements

3 Months Ended

Mar. 31, 2015

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaboration Agreements

2.	Collaboration Agreements

Astellas Agreements

Japan Agreement

In June 2005, we 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.

Europe Agreement

In April 2006, we 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. Under the Europe Agreement, Astellas committed to fund fifty percent 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, we entered into a collaboration agreement with AstraZeneca for the development and commercialization of roxadustat for the treatment of anemia in the United States 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 we expect to receive in various amounts through June 2016, of which $82.0 million was received as of December 31, 2013 and were 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 have extended payment terms and, accordingly, are not considered to be fixed or determinable upon the execution of the agreement. As such, for these remaining payments, the amount of revenue recognized is limited to the amount of cash consideration received; additionally, for each of the amounts received, the amount of revenue recognized will be determined on the basis of applying the relative selling price method to each of the units of accounting underlying the agreement as further described below. Further, $62.0 million of the remaining payment is contingent upon the occurrence of a specified event and accordingly is also not considered fixed or determinable. 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.

Under the U.S./RoW Agreement, we 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. Any additional development costs incurred by us during the development period in excess of the $233.0 million (aggregated spend) will be fully reimbursed by AstraZeneca. AstraZeneca will pay us tiered royalty payments on AstraZeneca’s future net sales (as defined in the agreement) of roxadustat in the low 20% range. In addition we 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, we (through our 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, 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, is 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. 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.

Accounting for the Astellas Agreements

For each of the Astellas agreements, we evaluated the deliverables within the respective arrangements and 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, we 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 we 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 $109.3 million (for the Europe Agreement) as of March 31, 2015.

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%. Our 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 our 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 our 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, we concluded at the time of the agreement that our collaboration partner, Astellas, would have the knowledge and capabilities to exploit the licenses without our 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, we considered the intent of the parties and the substantive reasons that led to that feature of the agreement.

•

In the case of the Japan Agreement, we 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, we 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. We and Astellas could have structured the arrangement with a transfer of manufacturing rights and compensated us through a royalty or other feature without significantly diminishing the prospects of the drug product. Therefore, we determined that the license in Japan provides stand-alone value to the customer despite the lack of manufacturing rights.

•

License to our 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 us 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 our 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 our 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, we 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 605-25-30-2 and 30-5.

Under the Europe Agreement, we are 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. Clinical milestone payments of $40.0 million and $50.0 million were received in 2010 and 2012. We evaluated the criteria under ASC 605-28 (as disclosed in Note 1) and concluded that each of those milestones was substantive.

Under the Japan Agreement, we are 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. A clinical milestone payment of $12.5 million was received in 2013. We evaluated the criteria under ASC 605-28 (as disclosed in Note 1) and concluded that the aforementioned milestone was substantive.

Accounting for the AstraZeneca Agreements

We considered the criteria in AICPA TIS Section 5100.39 in evaluating 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 as the presumption under the guidance is 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.

We 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 IRR 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. Our 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 our 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. We concluded that AstraZeneca has the knowledge and capabilities to exploit the U.S./RoW license without our further involvement.

•

Co-development services. This deliverable relates to co-development services which were reasonably expected to be performed by us at the time the U.S./RoW Agreement was signed. Revenue is recognized as reimbursements for such co-development services are earned. The period related to this deliverable represented our determination of the non-contingent performance period, which was estimated to be 65 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 our 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, we 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 U.S./RoW Agreement, we are 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 a non-substantive deferred approval milestone, which would be paid if certain competitors do not launch a 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 our 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, we considered the intent of the parties and the substantive reasons that led to that feature of the agreement.

For the China Agreement, we 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 us was a significant factor in the collaboration strategy, rather than simply a mechanism to properly compensate us, we 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 China Agreement, we are also eligible to receive from AstraZeneca an aggregate of approximately $328.5 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 $167.5 million in milestone payments upon the achievement of specified commercial sales events.

As we are 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 605-25-30-2 and 30-5.

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 condensed consolidated statements of operations. All other elements identified below are included in the “Collaboration services and other revenue” line item in the condensed consolidated statements of operations.

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


		Three Months Ended March 31,
Agreement	Deliverable	2015		2014
Japan	License	$	437	$	75
	Milestones		—		—

	Total license and milestone revenue	$	437	$	75
	Collaboration services revenue*	$	58	$	87

As of March 31, 2015, 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 March 31, 2015		Deferred Revenue at March 31, 2015		Total Consideration Through March 31, 2015
License	$	41,659	$	—	$	41,659
When and if available compounds		11		30		41
Manufacturing—clinical supplies		1,831		108		1,939
Committee services		14		2		16

Total license and collaboration services revenue	$	43,515	$	140	$	43,655

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 condensed consolidated statements of operations.

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


		Three Months Ended March 31,
Agreement	Deliverable	2015		2014
Europe	License	$	4,255	$	2,667
	Milestones		—		—

	Total license and milestone revenue	$	4,255	$	2,667
	Collaboration services revenue*	$	576	$	664

As of March 31, 2015, 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 March 31, 2015		Deferred Revenue at March 31, 2015		Total Consideration Through March 31, 2015
License	$	387,894	$	—	$	387,894
When and if available compounds		294		444		738
Manufacturing—clinical supplies		8,636		655		9,291
Development services—in progress		31,078		—		31,078
Committee services		247		22		269

Total license and collaboration services revenue	$	428,149	$	1,121	$	429,270

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 condensed consolidated statements of operations.

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


		Three Months Ended March 31,
Agreement	Deliverable	2015		2014
U.S. / RoW	License	$	6,814	$	11,943
	Milestones		—		—

	Total license and milestone revenue	$	6,814	$	11,943
	Collaboration services revenue*	$	4,138	$	2,435
	China single unit of accounting**		—		—

As of March 31, 2015, the total arrangement consideration has been allocated to each of the following deliverables under the U.S./RoW Agreement, along with any associated deferred revenue as follows (in thousands):


	Cumulative Revenue Through March 31, 2015		Deferred Revenue at March 31, 2015		Total Consideration Through March 31, 2015
License	$	182,188	$	—	$	182,188
Co-development, information sharing & committee services		24,698		30,693		55,391
Manufacturing—clinical supplies		104		86		190
China-single unit of accounting		—		37,344		37,344

Total license and collaboration services revenue	$	206,990	$	68,123	$	275,113

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 condensed 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.

In May 2015, we earned a $15.0 million development milestone under the U.S./RoW Agreement as a result of the finalization of our two audited carcinogenicity study reports.

Other Revenues

Other revenues consist of royalty payments received, which are recorded on a monthly basis as they are reported to us, and collagen feasibility sales. Other revenues were immaterial for all periods presented.

Deferred Revenue

Deferred revenue represents amounts billed to our 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

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Fair Value Measurements

3.	Fair Value Measurements

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


	March 31, 2015
	Level 1		Level 2		Level 3		Total
Corporate bonds	$	—	$	153,631	$	—	$	153,631
Equity investments		209		—		—		209

Sub-total		209		153,631		—		153,840
Money market funds		9,255		—		—		9,255

Total	$	9,464	$	153,631	$	—	$	163,095


	December 31, 2014
	Level 1		Level 2		Level 3		Total
Corporate bonds	$	—	$	158,432	$	—	$	158,432
Equity investments		201		—		—		201

Sub-total		201		158,432		—		158,633
Money market funds		13,802		—		—		13,802

Total	$	14,003	$	158,432	$	—	$	172,435

Our 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 our financial liabilities that are carried at historical cost are as follows (in thousands):


	March 31, 2015
	Level 1		Level 2		Level 3		Total
Lease financing obligations	$	—	$	—	$	97,276	$	97,276

	December 31, 2014
	Level 1		Level 2		Level 3		Total
Cease-use liability	$	—	$	—	$	184	$	184
Lease financing obligations		—		—		97,221		97,221

Total	$	—	$	—	$	97,405	$	97,405

The fair values of our financial liabilities were 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 any of the periods presented.

Description of Operations and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended				0 Months Ended	3 Months Ended
	Nov. 19, 2014	Mar. 31, 2015 Segment	Dec. 31, 2014	Nov. 19, 2014	Nov. 19, 2014 FibroGen Europe [Member]	Nov. 10, 2014 Common stock [Member]	Mar. 31, 2015 Common stock [Member]
Accounting Policy [Line Items]
Description reverse stock split							On November 10, 2014, we effected a 1-for-2.5 reverse split of our common stock. Upon the effectiveness of the reverse stock split, (i) every 2.5 shares of outstanding common stock were combined into one share of common stock, (ii) the number of shares of common stock for which each outstanding option or warrant to purchase common stock is exercisable was proportionally decreased on a 1-for-2.5 basis, (iii) the exercise price of each outstanding option or warrant to purchase common stock was proportionately increased on a 1-for- 2.5 basis, (iv) the exchange ratio for each share of outstanding FibroGen Europe Oy (“FibroGen Europe”) share of stock which is exchangeable into our common stock was proportionately reduced on a 1-for-2.5 basis, and (v) the conversion ratio for each share of outstanding preferred stock which is convertible into our common stock was proportionately reduced on a 1-for-2.5 basis. All of the outstanding common stock share numbers (including shares of common stock which our outstanding preferred stock shares were convertible into), common stock warrants, share prices, exercise prices and per share amounts have been adjusted in these condensed consolidated financial statements, on a retroactive basis, to reflect this 1-for-2.5 reverse stock split for all periods presented. The par value per share and the authorized number of shares of common stock and preferred stock were not adjusted as a result of the reverse stock split.
Reverse stock split ratio						0.4
Common stock shares sold	9,315,000
Public offering price				$ 18.00
Net proceeds from initial public offering and concurrent private placement	$ 171.8
Underwriting discounts and commissions	11.7
Offering expenses	4.1
Common stock, aggregate purchase price	$ 20.0
Convertible preferred stock converted into shares of common stock				33,919,954	958,996
Number of operating segment		1
Preferred stock, authorized shares		125,000,000	125,000,000
Preferred stock, par value		$ 0.01	$ 0.01
Convertible preferred stock outstanding		0	0

Description of Operations and Summary of Significant Accounting Policies - Schedule of Anti-dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Detail) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities	16,552	46,110
RSUs granted [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities	1,002
Employee stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities	15,377	11,058
Senior Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities		15,336
Junior Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities		18,584
Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities	173	173
FibroGen Europe preferred stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities		959

Collaboration Agreements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	0 Months Ended		1 Months Ended	3 Months Ended	0 Months Ended						0 Months Ended		1 Months Ended	3 Months Ended		1 Months Ended		3 Months Ended	12 Months Ended	1 Months Ended				3 Months Ended	12 Months Ended		108 Months Ended	1 Months Ended
	Mar. 31, 2015 AstraZeneca Agreements [Member]	Dec. 31, 2013 AstraZeneca Agreements [Member] U.S./RoW [Member]	Jul. 30, 2013 AstraZeneca Agreements [Member] U.S./RoW [Member]	Jul. 30, 2013 AstraZeneca Agreements [Member] U.S./RoW [Member]	Mar. 31, 2015 AstraZeneca Agreements [Member] U.S./RoW [Member]	Jul. 30, 2013 AstraZeneca Agreements [Member] U.S./RoW [Member] Clinical and Development Milestone [Member]	Jul. 30, 2013 AstraZeneca Agreements [Member] U.S./RoW [Member] Regulatory Milestone [Member]	Mar. 31, 2014 AstraZeneca Agreements [Member] China [Member]	Dec. 31, 2013 AstraZeneca Agreements [Member] China [Member]	Jul. 30, 2013 AstraZeneca Agreements [Member] China [Member]	Jul. 30, 2013 AstraZeneca Agreements [Member] China [Member]	Jul. 30, 2013 AstraZeneca Agreements [Member] China [Member] Clinical and Development Milestone [Member]	Jul. 30, 2013 AstraZeneca Agreements [Member] China [Member] Regulatory Milestone [Member]	Feb. 28, 2009 Astellas Agreement [Member]	Mar. 31, 2015 Astellas Agreement [Member] Minimum [Member]	Mar. 31, 2015 Astellas Agreement [Member] Maximum [Member]	Feb. 28, 2009 Astellas Agreement [Member] Japan [Member]	Jun. 30, 2005 Astellas Agreement [Member] Japan [Member]	Mar. 31, 2015 Astellas Agreement [Member] Japan [Member]	Dec. 31, 2013 Astellas Agreement [Member] Japan [Member]	Jun. 30, 2005 Astellas Agreement [Member] Japan [Member] Clinical and Development Milestone [Member]	Jun. 30, 2005 Astellas Agreement [Member] Japan [Member] Regulatory Milestone [Member]	Feb. 28, 2009 Astellas Agreement [Member] Europe [Member]	Apr. 30, 2006 Astellas Agreement [Member] Europe [Member]	Mar. 31, 2015 Astellas Agreement [Member] Europe [Member]	Dec. 31, 2012 Astellas Agreement [Member] Europe [Member]	Dec. 31, 2010 Astellas Agreement [Member] Europe [Member]	Mar. 31, 2015 Astellas Agreement [Member] Europe [Member]	Apr. 30, 2006 Astellas Agreement [Member] Europe [Member] Clinical and Development Milestone [Member]	Apr. 30, 2006 Astellas Agreement [Member] Europe [Member] Regulatory Milestone [Member]	Apr. 30, 2006 Astellas Agreement [Member] Europe [Member] Marketing approval milestone [Member]	May 31, 2015 U.S./Rest of World Agreement [Member] Development Milestone [Member] Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments		$ 82.0												$ 360.1			$ 40.1						$ 320.0
Development and regulatory approval milestones				550.0							161.0							117.5						425.0
Commercial sales milestone			325.0							167.5								15.0
Additional consideration based on net sales description					Low 20% range														Low 20% range						Low 20% range
Percentage of joint development costs committed to fund																								50.00%
Expected upfront, non-contingent and time-based payments			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							12.0
Contingent payment			62.0							20.0
Shared development costs			233.0
Proceeds from upfront payments										28.2
Payment received on execution of agreement								12.0	16.2
Development costs																												109.3
Discount rate applied	17.50%														17.50%	20.00%
Non-contingent performance period				65 months																				36 months
Total potential milestones			875.0							328.5								132.5						425.0
Substantive milestones						65.0	325.0					15.0	146.0								22.5	95.0							90.0	335.0	25.0
Clinical development milestones																				12.5						50.0	40.0
Royalty rate against projected net revenues	40.00%
Non-substantive milestones			160.0
Receipt of development milestone payment																																$ 15.0

Collaboration Agreements - Summary of Revenue Recognized under Agreement (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total license and milestone revenue	$ 11,506	$ 14,685
Collaboration services revenue	4,792	3,191
Revenue recognized	16,298	17,876
Astellas Agreement [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total license and milestone revenue	4,692	2,742
Collaboration services revenue	634	750
Astellas Agreement [Member] \| Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
License revenue	437	75
Milestones revenue	0	0
Total license and milestone revenue	437	75
Collaboration services revenue	58	87
Astellas Agreement [Member] \| Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
License revenue	4,255	2,667
Milestones revenue	0	0
Total license and milestone revenue	4,255	2,667
Collaboration services revenue	576	664
AstraZeneca Agreements [Member] \| China-single unit of accounting [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Revenue recognized	0	0
AstraZeneca Agreements [Member] \| U.S./RoW [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
License revenue	6,814	11,943
Milestones revenue	0	0
Total license and milestone revenue	6,814	11,943
Collaboration services revenue	$ 4,138	$ 2,435

Collaboration Agreements - Total Arrangement Consideration Allocated to Deliverables along with Associated Deferred Revenue (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Astellas Agreement [Member] \| Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	$ 43,515
Deferred Revenue	140
Total Consideration	43,655
Astellas Agreement [Member] \| Japan [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	41,659
Total Consideration	41,659
Astellas Agreement [Member] \| Japan [Member] \| When and if available compounds [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	11
Deferred Revenue	30
Total Consideration	41
Astellas Agreement [Member] \| Japan [Member] \| Manufacturing-clinical supplies [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	1,831
Deferred Revenue	108
Total Consideration	1,939
Astellas Agreement [Member] \| Japan [Member] \| Committee services [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	14
Deferred Revenue	2
Total Consideration	16
Astellas Agreement [Member] \| Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	428,149
Deferred Revenue	1,121
Total Consideration	429,270
Astellas Agreement [Member] \| Europe [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	387,894
Total Consideration	387,894
Astellas Agreement [Member] \| Europe [Member] \| When and if available compounds [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	294
Deferred Revenue	444
Total Consideration	738
Astellas Agreement [Member] \| Europe [Member] \| Manufacturing-clinical supplies [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	8,636
Deferred Revenue	655
Total Consideration	9,291
Astellas Agreement [Member] \| Europe [Member] \| Committee services [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	247
Deferred Revenue	22
Total Consideration	269
Astellas Agreement [Member] \| Europe [Member] \| Development services-in progress [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	31,078
Total Consideration	31,078
AstraZeneca Agreements [Member] \| U.S./RoW [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	206,990
Deferred Revenue	68,123
Total Consideration	275,113
AstraZeneca Agreements [Member] \| U.S./RoW [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	182,188
Total Consideration	182,188
AstraZeneca Agreements [Member] \| U.S./RoW [Member] \| Manufacturing-clinical supplies [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	104
Deferred Revenue	86
Total Consideration	190
AstraZeneca Agreements [Member] \| U.S./RoW [Member] \| Co-development, information sharing & committee services [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	24,698
Deferred Revenue	30,693
Total Consideration	55,391
AstraZeneca Agreements [Member] \| U.S./RoW [Member] \| China-single unit of accounting [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred Revenue	37,344
Total Consideration	$ 37,344

Fair Value Measurements - Fair Values of Financial Assets Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 153,840	$ 158,633
Assets fair value disclosure	128,369	165,455	72,953	76,332
Assets fair value disclosure	163,095	172,435
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	153,631	158,432
Equity investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	209	201
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value disclosure	9,255	13,802
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	209	201
Assets fair value disclosure	9,464	14,003
Level 1 [Member] \| Equity investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	209	201
Level 1 [Member] \| Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value disclosure	9,255	13,802
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	153,631	158,432
Assets fair value disclosure	153,631	158,432
Level 2 [Member] \| Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 153,631	$ 158,432

Fair Value Measurements - Fair Values of Financial Liabilities Carried at Historical Cost (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value disclosure		$ 97,405
Cease-use liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value disclosure		184
Lease financing obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value disclosure	97,276	97,221
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value disclosure		97,405
Level 3 [Member] \| Cease-use liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value disclosure		184
Level 3 [Member] \| Lease financing obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value disclosure	$ 97,276	$ 97,221

Balance Sheet Components - Schedule of Cash and Cash Equivalents (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]
Cash	$ 119,114	$ 151,653
Money market funds	9,255	13,802
Total cash and cash equivalents	$ 128,369	$ 165,455	$ 72,953	$ 76,332

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, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 153,049	$ 158,816
Gross Unrealized Holding Gains	865	331
Gross Unrealized Holding Losses	(74)	(514)
Estimated Fair Value	153,840	158,633
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	152,924	158,692
Gross Unrealized Holding Gains	781	254
Gross Unrealized Holding Losses	(74)	(514)
Estimated Fair Value	153,631	158,432
Equity investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	125	124
Gross Unrealized Holding Gains	84	77
Estimated Fair Value	$ 209	$ 201

Balance Sheet Components - Schedule of Accrued Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Preclinical and clinical trial accruals	$ 26,823	$ 25,418
Payroll and related accruals	8,876	15,608
Professional services	3,271	2,401
Other	3,496	5,558
Total accrued liabilities	$ 42,466	$ 48,985

Stock-Based Compensation - Schedule of Allocated Stock-Based Compensation Expense Related to Options Granted (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,446	$ 795
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	4,222	475
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,224	$ 320

Income Taxes - Additional information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Tax Disclosure [Abstract]
Provision for income taxes	$ (271)	$ 0