Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2018	Jul. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	FGEN
Entity Registrant Name	FIBROGEN INC
Entity Central Index Key	0000921299
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		84,333,402

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 643,803	$ 673,658
Short-term investments	28,094	62,060
Accounts receivable ($25,886 and $4,004 from a related party)	30,189	8,452
Prepaid expenses and other current assets ($15,000 and $0 from a related party)	17,997	4,800
Total current assets	720,083	748,970
Restricted time deposits	5,181	5,181
Long-term investments	10,587	10,506
Property and equipment, net	128,829	129,476
Other assets	5,239	4,517
Total assets	869,919	898,650
Current liabilities:
Accounts payable	3,222	5,509
Accrued liabilities ($327 and $272 to a related party)	49,492	63,781
Deferred revenue	37,845	16,670
Total current liabilities	90,559	85,960
Long-term portion of lease financing obligations	97,473	97,763
Product development obligations	16,981	17,244
Deferred rent	3,350	3,657
Deferred revenue, net of current	137,436	138,241
Other long-term liabilities	9,318	8,047
Total liabilities	355,117	350,912
Commitments and Contingencies
Stockholders’ equity:
Preferred stock, $0.01 par value; 125,000 shares authorized; no shares issued and outstanding at June 30, 2018 and December 31, 2017	0	0
Common stock, $0.01 par value; 225,000 shares authorized at June 30, 2018 and December 31, 2017; 84,183 and 82,498 shares issued and outstanding at June 30, 2018 and December 31, 2017	842	825
Additional paid-in capital	1,191,524	1,160,094
Accumulated other comprehensive loss	(2,611)	(1,795)
Accumulated deficit	(694,224)	(630,657)
Total stockholders’ equity	495,531	528,467
Non-controlling interests	19,271	19,271
Total equity	514,802	547,738
Total liabilities, stockholders’ equity and non-controlling interests	$ 869,919	$ 898,650

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Accounts receivable from related party	$ 25,886	$ 4,004
Prepaid expenses and other current assets from related party	15,000	0
Accrued liabilities to related party	$ 327	$ 272
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	84,183,000	82,498,000
Common stock, shares outstanding	84,183,000	82,498,000

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Total revenue	$ 43,952	$ 30,268	$ 75,876	$ 59,710
Operating expenses:
Research and development	52,138	46,981	109,112	93,713
General and administrative	15,055	13,425	30,605	24,955
Total operating expenses	67,193	60,406	139,717	118,668
Loss from operations	(23,241)	(30,138)	(63,841)	(58,958)
Interest and other, net
Interest expense	(2,750)	(2,757)	(5,519)	(5,132)
Interest income and other, net	2,646	1,031	4,717	1,677
Total interest and other, net	(104)	(1,726)	(802)	(3,455)
Loss before income taxes	(23,345)	(31,864)	(64,643)	(62,413)
Provision for income taxes	75	48	174	109
Net loss	$ (23,420)	$ (31,912)	$ (64,817)	$ (62,522)
Net loss per share - basic and diluted	$ (0.28)	$ (0.46)	$ (0.78)	$ (0.94)
Weighted average number of common shares used to calculate net loss per share - basic and diluted	83,750	69,638	83,309	66,853
License Revenue [Member]
Revenue:
Total revenue	$ 14,323	$ 0	$ 14,323	$ 0
Development and Other Revenue [Member]
Revenue:
Total revenue	$ 29,629	$ 30,268	$ 61,553	$ 59,710

Condensed Consolidated Statements of Operations (Unaudited) (Parenthetical) - Astellas Agreement [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
License and milestone revenue from a related party	$ 14,323	$ 0	$ 14,323	$ 0
Collaboration services and other revenue from a related party	$ 6,145	$ 5,099	$ 11,317	$ 9,784

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (23,420)	$ (31,912)	$ (64,817)	$ (62,522)
Other comprehensive income (loss):
Foreign currency translation adjustments	958	(994)	431	(1,249)
Available-for-sale investments:
Unrealized gain on investments, net of tax effect	53	654	3	832
Reclassification from accumulated other comprehensive loss	0	(26)	0	(10)
Net change in unrealized gain on available-for-sale investments	53	628	3	822
Other comprehensive income (loss), net of taxes	1,011	(366)	434	(427)
Comprehensive loss	$ (22,409)	$ (32,278)	$ (64,383)	$ (62,949)

Condensed Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net loss	$ (64,817)	$ (62,522)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	3,083	3,072
Amortization of premium on investments	463	1,064
Unrealized loss (gain) on short-term investments	1,127	(1)
Loss (gain) on disposal of property and equipment	53	(4)
Stock-based compensation	24,109	17,980
Realized foreign currency gain	(1,074)	0
Realized gain on sales of available-for-sale securities	(87)	(95)
Changes in operating assets and liabilities:
Accounts receivable	(21,737)	1,515
Prepaid expenses and other current assets	(13,197)	(124)
Other assets	(722)	(1,130)
Accounts payable	(2,287)	(2,962)
Accrued liabilities	(13,371)	(3,061)
Deferred revenue	20,370	(961)
Lease financing liability	25	401
Other long-term liabilities	1,135	(65)
Net cash used in operating activities	(66,927)	(46,893)
Investing activities
Purchases of property and equipment	(3,705)	(1,612)
Proceeds from sale of property and equipment	184	5
Purchases of available-for-sale securities	(98)	(66)
Proceeds from sales of available-for-sale securities	8,167	18,152
Proceeds from maturities of available-for-sale securities	25,390	23,849
Net cash provided by investing activities	29,938	40,328
Financing activities
Repayments of lease liability	(201)	(201)
Proceeds from follow-on offerings, net of underwriting discounts and commission costs	0	115,050
Cash paid for payroll taxes on restricted stock unit releases	(10,005)	(3,673)
Proceeds from issuance of common stock	17,343	12,244
Payments of deferred offering costs	0	(386)
Net cash provided by financing activities	7,137	123,034
Effect of exchange rate change on cash and cash equivalents	(3)	26
Net decrease in cash and cash equivalents	(29,855)	116,495
Total cash and cash equivalents at beginning of period	673,658	173,782
Total cash and cash equivalents at end of period	$ 643,803	$ 290,277

Significant Accounting Policies

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Significant Accounting Policies

1.	Significant Accounting Policies

Description of Operations

FibroGen, Inc. (“FibroGen” or the “Company”) was incorporated in 1993 in Delaware and is a 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”) and myelodysplastic syndromes (“MDS”). 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 and Duchenne muscular dystrophy (“DMD”). The Company is taking 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.

Basis of Presentation and Principles of Consolidation

The condensed consolidated financial statements include the accounts of FibroGen, its wholly owned subsidiaries and its majority-owned subsidiaries, FibroGen Europe Oy 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.

The unaudited condensed consolidated financial statements and related disclosures have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) applicable to interim financial reporting and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the United States Securities and Exchange Commission (“SEC”) and, therefore, do not include all information and footnote disclosures normally included in the annual consolidated financial statements. The financial information included herein should be read in conjunction with the consolidated financial statements and related notes in the Company’s Annual Report on Form 10-K filed with the SEC for the year ended December 31, 2017 (“2017 Form 10-K”).

The accounting policies used by the Company in its presentation of interim financial results are consistent with those presented in Note 2 to the consolidated financial statements included in the 2017 Form 10-K, except for the following:

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 performance obligations comprised of promised services, or bundles of services, that are distinct. Services that are not distinct are combined with other services in the agreement until they form a distinct bundle of services. The Company’s process for identifying performance obligations and an enumeration of each obligation for each agreement is outlined in Note 2 “Collaboration Agreements.” Determining the performance obligations within a collaboration agreement often involves significant judgment and is specific to the facts and circumstances contained in each agreement.

The Company has identified the following material promises under its collaboration agreements: (1) license of FibroGen technology, (2) the performance of co-development services, including manufacturing of clinical supplies and other services during the development period, and (3) manufacture of commercial supply. The evaluation as to whether these promises are distinct, and therefore represent separate performance obligations, is described in more details in Note 2 “Collaboration Agreements.”

For revenue recognition purposes, the Company determines that the term of its collaboration agreements begin on the effective date and ends upon the completion of all performance obligations contained in the agreements. In each agreement, the contract term is defined as the period in which parties to the contract have present and enforceable rights and obligations. The Company believes that the existence of what it considers to be substantive termination penalties on the part of the counterparty create sufficient incentive for the counterparty to avoid exercising its right to terminate the agreement unless in exceptionally rare situations.

The transaction price for each collaboration agreement is determined based on the amount of consideration the Company expects to be entitled for satisfying all performance obligations within the agreement. The Company’s collaboration agreements include payments to the Company of one or more of the following: non-refundable upfront license fees; co-development billings; development, regulatory, and commercial milestone payments; and royalties on net sales of licensed products.

Upfront license fees are non-contingent and non-refundable in nature and are included in the transaction price at the point when the license fees become due to the Company. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.

Co-development billings resulting from the Company’s research and development efforts, which are reimbursable under its collaboration agreements, are considered variable consideration. Determining the amount of variable consideration from co-development billings requires the Company to make estimates of future research and development efforts, which involves significant judgment. Co-development billings are allocated entirely to the co-development services performance obligation when amounts are related specifically to research and development efforts necessary to satisfy the performance obligation, and such an allocation is consistent with the allocation objective.

Milestone payments are also considered variable consideration, which requires the Company to make estimates of when achievement of a particular milestone becomes probable. Similar to other forms of variable consideration, milestone payments are included in the transaction price when it becomes probable that such inclusion would not result in a significant revenue reversal. Milestone payments are therefore included in the transaction price when achievement of the milestone becomes probable.

For arrangements that include sales-based royalties and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from its collaboration arrangements.

The transaction price is allocated to performance obligations based on their relative standalone selling price (“SSP”), with the exception of co-development billings allocated entirely to co-development services performance obligations. The SSP is determined based on observable prices at which the Company separately sells the products and services. If an SSP is not directly observable, then the Company will estimate the SSP considering marketing conditions, entity-specific factors, and information about the customer or class of customer that is reasonably available. The process for determining SSP involves significant judgment 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.

Significant judgment may be required in determining whether a performance obligation is distinct, determining the amount of variable consideration to be included in the transaction price, and estimating the SSP of each performance obligation. An enumeration of the Company’s significant judgments is outlined in Note 2 “Collaboration Agreements.”

For each performance obligation identified within an arrangement, the Company determines the period over which the promised services are transferred and the performance obligation is satisfied. Service revenue is recognized over time based on progress toward complete satisfaction of the performance obligation. The Company uses an input method to measure progress toward the satisfaction of co-development services and certain other related performance obligations, which is based on costs of labor hours or full time equivalents and out-of-pocket expenses incurred relative to total expected costs to be incurred. The Company believes this measure of progress provides a faithful depiction of the transfer of services because other measures do not measure as accurately how the Company transfers its performance obligations to its collaboration partners.

Investments

The Company’s investments consist of available-for-sale debt investments and marketable equity investments. 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 for available-for-sale debt investments that are deemed temporary in nature are recorded in accumulated other comprehensive income (loss) as a separate component of stockholder’ equity. Marketable equity securities are equity securities with readily determinable fair value, and are measured and recorded at fair value. Realized and unrealized gains or losses resulting from changes in value and sale of the Company’s marketable equity investments are recorded in other income (expenses) in the consolidated statement of operations.

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.

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. In the Company’s opinion, the accompanying unaudited condensed consolidated financial statements include all normal recurring adjustments necessary for a fair statement of its financial position, results of operations and cash flows for the interim periods presented.

Recently Issued and Adopted Accounting Guidance

New Revenue Standards

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“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 No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing; ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients; and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers (collectively, the “new revenue standards”).

Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

The Company adopted the new revenue standards as of January 1, 2018 using the full retrospective method, which required the Company to recast the prior reporting period presented in the condensed consolidated financial statements. The primary impact upon adoption of the new revenue standards relates to the manner in which revenue is recognized for co-development billings and milestone payments under the Company’s collaboration arrangements. Under the new revenue standards, both of these elements of consideration are considered variable consideration which requires the Company to make estimates of when co-development billings become due or when achievement of a particular milestone becomes probable. Payments are included in the transaction price when it becomes probable that inclusion would not lead to a significant revenue reversal.

The Company has recast its condensed consolidated statement of operations and condensed balance sheet from amounts previously reported due to the adoption of the new revenue standards. The adoption of the new revenue standards had no impact to the Company’s previously reported condensed consolidated statement of cash flows.

Select line items from the Company’s condensed consolidated statement of operations and condensed balance sheet, which reflect the adoption of the new revenue standards are as follows (in thousands):

	Three Months Ended June 30, 2017									Six Months Ended June 30, 2017
	As Previously Reported			New Revenue Standards Adjustment			As Recast			As Previously Reported			New Revenue Standards Adjustment			As Recast
Statement of Operations
License revenue	$	21,352		$	(21,352	)	$	—		$	40,933		$	(40,933	)	$	—
Development and other revenue		7,645			22,623			30,268			14,955			44,755			59,710
Total revenue		28,997			1,271			30,268			55,888			3,822			59,710
Net loss		(33,183	)		1,271			(31,912	)		(66,344	)		3,822			(62,522	)
Net loss per share - basic and diluted	$	(0.48	)	$	0.02		$	(0.46	)	$	(0.99	)	$	0.05		$	(0.94	)

										December 31, 2017
										As Previously Reported			New Revenue Standards Adjustment			As Recast
Balance Sheet
Deferred revenue, current										$	7,968		$	8,702		$	16,670
Deferred revenue, net of current											112,231			26,010			138,241
Accumulated deficit											(595,945	)		(34,712	)		(630,657	)

The adoption of the new revenue standards resulted in an increase in revenue of $5.3 million and $3.6 million for the years ended December 31, 2017 and 2016, respectively, and an increase in the opening accumulated deficit of $43.7 million as of January 1, 2016.

ASU 2016-01

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 was effective for the annual reporting period beginning after December 15, 2017 and interim periods within those annual periods. The Company adopted this guidance as of January 1, 2018 using the modified retrospective approach. The impacts to the Company’s accumulated other comprehensive loss and accumulated deficit upon adoption of this guidance are as follows (in thousands):

	Accumulated Other Comprehensive Loss			Accumulated Deficit
Balance at December 31, 2017	$	(1,795	)	$	(630,657	)	*
Impact of change in accounting principle upon adoption of ASU 2016-01		(1,250	)		1,250
Opening balance as of January 1, 2018	$	(3,045	)	$	(629,407	)

*	Recast to reflect the adoption of the new revenue standards. See above.

The adoption of this guidance had no impact to the Company’s condensed consolidated statement of operations or condensed consolidated statement of cash flows for the six months ended June 30, 2018.

ASU 2017-09

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 was effective for annual reporting period beginning after December 15, 2017, including interim periods. The Company adopted this guidance as of January 1, 2018, and the adoption of this guidance had no impact to the Company’s condensed consolidated financial statements.

ASU 2016-16

In October 2016, the FASB issued ASU 2016-16, Intra-Entity Transfers of Assets Other Than Inventory. This guidance requires companies to recognize the income tax effects of intercompany sales or transfer of assets, other than inventory, in the income statement as income tax expense (or benefit) in the period the sale or transfer occurs. The exception to recognizing the income tax effects of intercompany sales or transfer sales or transfer of assets remains in place for intercompany inventory sales and transfers. This guidance was effective for annual reporting period beginning after December 15, 2017, including interim periods. The Company adopted this guidance as of January 1, 2018 using the modified retrospective method. The adoption of this guidance did not result in any recognition of previously unrecognized deferred charges using a modified retrospective method, thus had no impact to the Company’s condensed consolidated financial statements.

Recently Issued Accounting Guidance Not Yet Adopted

In June 2018, the FASB issued ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. This guidance expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. The guidance also specifies that Topic 718 applies to all share-based payment transactions in which a grantor acquires goods or services to be used or consumed in a grantor’s own operations by issuing share-based payment awards. This guidance is effective for annual reporting period beginning after December 15, 2018, including interim periods. The Company will adopt this guidance on January 1, 2019 and does not anticipate a material impact to its consolidated financial statements upon adoption.

In February 2018, the FASB issued ASU 2018-02, Income Statement - Reporting Comprehensive Income: Reclassification of Certain Tax effects from Accumulated Other Comprehensive Income. This guidance allows for the reclassification from accumulated other comprehensive income to retained earnings for the stranded tax effects arising from the change in the reduction of the United States (“U.S.”) federal statutory income tax rate from 35% to 21%. This guidance is effective for annual reporting period beginning after December 15, 2018, including interim periods, with early adoption permitted. The Company will adopt this guidance on January 1, 2019 and does not anticipate a material reclassification between its accumulated other comprehensive loss and accumulated deficit upon adoption.

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) (“ASU 2016-02”). 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. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements (“ASU 2018-11”), which provides entities the option to initially apply ASU 2016-02 at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. ASU 2016-02 and ASU 2018-11 are effective for the annual reporting period beginning after December 15, 2018, including interim periods within that reporting period. The Company will adopt this guidance as of January 1, 2019 and is currently in the preliminary stages of gathering data and assessing the impact of the new lease accounting standard. The Company anticipates that the adoption of this guidance will result in additional assets and liabilities being recorded on its consolidated balance sheet.

Collaboration Agreements

6 Months Ended

Jun. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Collaboration Agreements

2.	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, which amounts were fully received as of February 2009. 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 milestone payments upon achievement of specified clinical and development milestone events, which amounts were fully received as of July 2016, (ii) up to $95.0 million in 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.

During the second quarter of 2018, Astellas reported positive results from the final phase 3 CKD-dialysis trial of roxadustat in Japan, indicating that Astellas is ready to make an NDA submission for the treatment of anemia with roxadustat in CKD-dialysis patients in 2018. The Company evaluated the regulatory milestone payment associated with NDA submission in Japan based on variable consideration requirements under the current revenue standards and concluded that this milestone became probable of being achieved in the second quarter of 2018. Accordingly, the consideration of $15.0 million associated with this milestone was included in the transaction price and allocated to performance obligations under the Japan Agreement in the second quarter of 2018, of which $14.9 million was recognized as revenue during the period from performance obligations satisfied or partially satisfied as of June 30, 2018.

FibroGen and Astellas are currently negotiating an amendment to the Japan Agreement that will allow Astellas to manufacture roxadustat drug product for commercialization in Japan, and for which FibroGen would continue to manufacture and deliver to Astellas roxadustat active pharmaceutical ingredient (“API”). The commercial terms of the Japan Agreement would remain substantially the same. In the second quarter of 2018, FibroGen delivered roxadustat API to Astellas under a material transfer agreement for Astellas to conduct commercial scale manufacturing validation for roxadustat drug product in anticipation of commercial launch in Japan. The associated consideration of $20.9 million was recorded as deferred revenue because Astellas’ right to use the material was limited as of June 30, 2018.

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). 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 milestone payments upon achievement of specified clinical and development milestone events, (ii) up to $335.0 million in milestone payments upon achievement of specified regulatory milestone events. Clinical milestone payments of $40.0 million and $50.0 million were received in 2010 and 2012, respectively. 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 (“RoW”) Agreement

Effective July 30, 2013, the Company entered into a collaboration agreement with AstraZeneca AB (“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 paid upfront, non-contingent, non-refundable and time-based payments totaling $374.0 million, which 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 milestone payments upon achievement of specified clinical and development milestone events, $15.0 million of which was received in 2015 as a result of the finalization of its two audited pre-clinical carcinogenicity study reports, (ii) up to $325.0 million in milestone payments upon achievement of specified regulatory milestone events, (iii) up to $160.0 million in milestone payments related to activity by potential competitors and (iv) up to approximately $325.0 million in milestone payments upon the achievement of specified commercial sales events.

Under the U.S./RoW Agreement, the Company and AstraZeneca shared 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). Development costs incurred by FibroGen during the development period in excess of the $233.0 million (aggregated spend) are 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 paid upfront, non-contingent and non-refundable payments totaling $28.2 million, which were fully received in 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 milestone payments upon achievement of specified clinical and development milestone events, (ii) up to $146.0 million in 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. 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 October 2017, the State Drug Administration in China accepted the Company’s 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. The Company evaluated this milestone based on variable consideration requirements under the new revenue standards and concluded that the milestone was probable of being achieved in the third quarter of 2017. Accordingly, consideration associated with this milestone was included in the transaction price and allocated to performance obligations under the China Agreement in the same period.

Accounting for the Astellas Agreements

For each of the Astellas agreements, the Company has evaluated the promised services within the respective arrangements and has identified performance obligations representing those services and bundles of services that are distinct.

Promised services that were not distinct have been combined with other promised services to form a distinct bundle of promised services, with revenue being recognized on the bundle of services rather than the individual services. There are no right-of-return provisions for the delivered items in the Astellas agreements.

As of June 30, 2018, the transaction price for the Japan Agreement included $40.1 million of non-contingent upfront payments, $37.5 million of variable consideration related to payments for milestones considered probable of being achieved, and $12.7 million of variable consideration related to co-development billings. The transaction price for the Europe Agreement included $320.0 million of non-contingent upfront payments, $90.0 million of variable consideration related to payments for milestones considered probable of being achieved, and $183.8 million of variable consideration related to co-development billings.

For revenue recognition purposes, the Company determined that the term of each collaboration agreement with Astellas begins on the effective date and ends upon the completion of all performance obligations contained in the agreement. The contract term is defined as the period in which parties to the contract have present and enforceable rights and obligations. The Company believes that the requirement to continue funding development for a substantive period of time and loss of product rights, along with non-refundable upfront payments already remitted by Astellas, create significant disincentive for Astellas to exercise its right to terminate the agreements.

For the Astellas agreements, the Company allocated the transaction price to the various performance obligations based on the relative SSP of each performance obligation, with the exception of co-development billings allocated entirely to co-development services performance obligations.

For the technology license under the Japan Agreement and Europe Agreement, SSP 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. SSP also considered certain future royalty payments associated with commercial performance of the Company’s compounds, transfer prices and expected gross margins.

The promised services that were analyzed, along with their general timing of satisfaction and recognition as revenue, are as follows:

(1)

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 term. In both cases, the Company concluded at the time of the agreement that its collaboration partner, Astellas, would have the knowledge and capabilities to fully exploit the licenses without the Company’s further involvement. However, the Japan Agreement has contractual limitations that might affect Astellas’ ability to fully exploit the license and therefore, potentially, the conclusion as to whether the license is capable of being distinct. 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 was not distinct in the context of the agreement, the Company considered the ability of Astellas to benefit from the license together with other resources readily available to Astellas. Finally, the Company considered the fact that at the time of delivery of the license, the development services were beyond the preclinical development phase and any remaining development work in either agreement would not be expected to result in any significant modification or customization to the licensed technology. As such, the development services are separately identifiable from the licensed technology, indicating that the license is a distinct performance obligation.

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 manufacturing process does not require specialized knowledge or expertise uniquely held by FibroGen, and notwithstanding contractual restrictions, Astellas could employ manufacturing services from readily available third parties in order to benefit from the license. Therefore, along with the foregoing paragraph, the Company determined that the license in Japan is a distinct performance obligation despite the retention of manufacturing rights by the Company.

In summary, the Company concludes that item (1) represents a performance obligation. The portion of the transaction price allocated to this performance obligation based on a relative SSP basis is recognized as revenue in its entirety at the point in time the license transfers to Astellas.

(2)

Co-development services (Europe Agreement). This promise relates to co-development services that were reasonably expected to be performed by the Company at the time the collaboration agreement was signed and is considered distinct. Co-development billings are allocated entirely to the co-development services performance obligation as amounts are related specifically to research and development efforts necessary to satisfy the performance obligation, and such an allocation is consistent with the allocation objective. Revenue is recognized over time based on progress toward complete satisfaction of the performance obligation. The Company uses an input method to measure progress toward the satisfaction of the performance obligation, which is based on costs of labor hours and out-of-pocket expenses incurred relative to total expected costs to be incurred. The measure of progress is updated each reporting period. Co-development services are expected to continue over the development period which is currently estimated to continue through the end of 2019. There was no provision for co-development services in the Japan Agreement.

(3)	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 promises are generally satisfied throughout the term of the agreements.

(4)	Manufacturing of clinical supplies of products. This promise 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.

(5)	Committee service. This promise is satisfied throughout the course of the agreements as meetings are attended.

Items (3)-(5) are bundled into a single performance obligation which is distinct given the fact that all are highly interrelated during the development period (pre-commercial phase of development) such that satisfying them independently is not practicable. Revenue is recognized over time based on progress toward complete satisfaction of the performance obligation. The Company uses an input method to measure progress toward the satisfaction of the performance obligation, which is based on costs of labor hours or full time equivalents and out-of-pocket expenses incurred relative to total expected costs to be incurred. The measure of progress is updated each reporting period.

(6)

Manufacturing commercial supplies of products. This promised service is distinct as services are not interrelated with any of the other performance obligations. Payments received for commercial supplies of products represent sales-based payments related predominately to the license of intellectual property under both Astellas agreements. Revenue is recognized as supplies are shipped for commercial use during the commercialization period. To date, no such revenue has been recognized.

Accounting for the AstraZeneca Agreements

The Company evaluated whether the U.S./RoW Agreement and China Agreement should be accounted for as a single or separate arrangements 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. The key points the Company considered in reaching this conclusion are as follows:

1.	While the two agreements were largely negotiated separately, those negotiations proceeded concurrently, and were intended to be completed contemporaneously, presuming AstraZeneca decided to proceed with licenses in all regions available.

Throughout negotiations for both agreements, the Company and the counterparties understood and considered the possibility that one arrangement may be executed without the execution of the other arrangement. However, the preference for the Company and the counterparties during the negotiations was to execute both arrangements concurrently.

The two agreements were executed as separate agreements because different development, regulatory and commercial approaches required certain terms of the agreements to be structured differently, rather than because the Company or the counterparties considered the agreements to be fundamentally separate negotiations.

Accordingly, as the agreements are being accounted for as a single arrangement, upfront and other non-contingent consideration received and to be received has been and will be pooled together and allocated to each of the performance obligations in both the U.S./RoW Agreement and China Agreement based on their relative SSPs.

For each of the AstraZeneca agreements, the Company has evaluated the promised services within the respective arrangements and has identified performance obligations representing those services and bundled services that are distinct.

Promised services that were not distinct have been combined with other promised services to form a distinct bundle of promised services, with revenue being recognized on the bundle of services rather than the individual promised services. There are no right-of-return provisions for the delivered items in the AstraZeneca agreements.

As of June 30, 2018, the transaction price for the U.S./RoW Agreement and China Agreement included $402.2 million of non-contingent upfront payments, $30.0 million of variable consideration related to payments for milestones considered probable of being achieved, and $673.0 million of variable consideration related to co-development billings.

For the AstraZeneca agreements, the Company allocated the transaction price to the various performance obligations based on the relative SSP of each performance obligation, with the exception of co-development billings. Co-development billings under the U.S./RoW Agreement were allocated entirely to the U.S./RoW co-development services performance obligation, and co-development billings under the China Agreement were allocated entirely to the combined performance obligation under the China Agreement.

For revenue recognition purposes, the Company determined that the term of its collaboration agreements with AstraZeneca begin on the effective date and ends upon the completion of all performance obligations contained in the agreements. The contract term is defined as the period in which parties to the contract have present and enforceable rights and obligations. The Company believes that the requirement to continue funding development for a substantive period of time and the loss of product rights, along with non-refundable upfront payments already remitted by AstraZeneca, represent substantive termination penalties that create significant disincentive for AstraZeneca to exercise its right to terminate the agreement.

For the technology license under the AstraZeneca U.S./RoW Agreement, SSP 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 promised services that were analyzed, along with their general timing of satisfaction and recognition as revenue, are as follows:

(1)

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 term. The Company concluded that AstraZeneca has the knowledge and capabilities to fully exploit the license under the U.S./RoW Agreement without the Company’s further involvement. Finally, the Company considered the fact that at the time of delivery of the license, the development services were beyond the preclinical development phase and any remaining development work would not be expected to result in any significant modification or customization to the licensed technology. As such, the development services are separately identifiable from the licensed technology, indicating that the license is a distinct performance obligation. Therefore, the Company has concluded that the license is distinct and represents a performance obligation. The portion of the transaction price allocated to this performance obligation based on a relative SSP basis is recognized as revenue in its entirety at the point in time the license transfers to AstraZeneca.

(2)

Co-development services. This promise relates to co-development services that were reasonably expected to be performed by the Company at the time the collaboration agreement was signed and is distinct. Co-development billings are allocated entirely to the co-development services performance obligation as amounts are related specifically to research and development efforts necessary to satisfy the performance obligation, and such an allocation is consistent with the allocation objective. Revenue is recognized over time based on progress toward complete satisfaction of the performance obligation. The Company uses an input method to measure progress toward the satisfaction of the performance obligation, which is based on costs of labor hours or full time equivalents and out-of-pocket expenses incurred relative to total expected costs to be incurred Co-development services are expected to continue over the development period which is estimated to continue through the end of 2020.

(3)	Manufacturing of clinical supplies of products. This promise 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.

(4)	Information sharing and committee service. These promises are satisfied throughout the course of the agreement as services are provided.

Items (3)-(4) are bundled into a single performance obligation which is distinct given the fact that all are highly interrelated during the development period (pre-commercial phase of development) such that delivering them independently is not practicable. Revenue is recognized over time based on progress toward complete satisfaction of the performance obligation. The Company uses an input method to measure progress toward the satisfaction of the performance obligation, which is based on costs of labor hours or full time equivalents and out-of-pocket expenses incurred relative to total expected costs to be incurred. The measure of progress is updated each reporting period.

(5)

Manufacturing commercial supplies of products. This promise is distinct as services are not interrelated with any of the other performance obligations. Payments received for commercial supplies of products represent sales-based royalties related predominately to the license of intellectual property under the agreement. Revenue is recognized as supplies are shipped for commercial use during the commercialization period. To date, no such revenue has been recognized.

China Agreement:

The performance obligation that were analyzed, along with their general timing of satisfaction and recognition as revenue, 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. However, the China Agreement with AstraZeneca has contractual limitations that might affect AstraZeneca’s ability to fully exploit the license and therefore, potentially, the conclusion as to whether the license is distinct in the context of the agreement. 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 was not distinct in the context of the agreement, the Company considered the ability of AstraZeneca to benefit from the license on its own or together with other resources readily available to AstraZeneca.

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. Due to certain regulatory restrictions in China, manufacturing services of commercial drug product in China are not readily available to AstraZeneca or any other parties. Therefore, AstraZeneca cannot benefit from the license on its own or together with other readily available resources. Accordingly, all the promises identified, including co-development services, under the China Agreement have been bundled into a single performance obligation and amounts of the transaction price allocable to this performance obligation are deferred until control of the manufactured commercial drug product has begun to transfer to AstraZeneca. Upon commencement of the transfer of control to commercial drug product, revenue would be recognized in a pattern consistent with estimated deliveries of the commercial drug product.

Summary of Revenue Recognized Under the Collaboration Agreements

The table below summarizes the accounting treatment for the various performance obligations pursuant to each of the Astellas and AstraZeneca agreements. License amounts identified below are included in the “License revenue” line item in the condensed consolidated statements of operations. All other elements identified below are included in the “Development 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 June 30,				Six Months Ended June 30,
Agreement	Performance Obligation	2018		2017 *		2018		2017 *
Japan	License revenue	$	14,323	$	—	$	14,323	$	—
	Development revenue	$	1,142	$	317	$	1,591	$	613

*	Recast to reflect the adoption of the new revenue standards. See Note 1.

The transaction price related to consideration received and accounts receivable has been allocated to each of the following performance obligations under the Japan Agreement, along with any associated deferred revenue as follows (in thousands):

Japan Agreement	Cumulative Revenue Through June 30, 2018		Deferred Revenue at June 30, 2018		Total Consideration Through June 30, 2018
License	$	74,089	$	—	$	74,089
Manufacturing--clinical supplies		13,099		473		13,572
Total license and development revenue	$	87,188	$	473	$	87,661

The revenue recognized under the Japan Agreement in the quarter ended June 30, 2018 included a $14.9 million true-up relating to prior periods resulting from changes to estimated variable consideration in the current period. The remainder of the transaction price related to the Japan Agreement includes $2.6 million of variable consideration from estimated future co-development billing and is expected to be recognized over the remaining development service period.

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

		Three Months Ended June 30,				Six Months Ended June 30,
Agreement	Performance Obligation	2018		2017 *		2018		2017 *
Europe	License revenue	$	—	$	—	$	—	$	—
	Development revenue	$	5,003	$	4,781	$	9,726	$	9,171

*	Recast to reflect the adoption of the new revenue standards. See Note 1.

The transaction price related to consideration received and accounts receivable has been allocated to each of the following performance obligations under the Europe Agreement, along with any associated deferred revenue as follows (in thousands):

Europe Agreement	Cumulative Revenue Through June 30, 2018		Deferred Revenue at June 30, 2018		Total Consideration Through June 30, 2018
License	$	370,481	$	—	$	370,481
Manufacturing--clinical supplies		194,059		5,337		199,396
Total license and development revenue	$	564,540	$	5,337	$	569,877

The revenue recognized under the Europe Agreement in the quarter ended June 30, 2018 included a reduction in revenue of $0.2 million as true-up relating to prior periods resulting from changes to estimated variable consideration in the current period. The remainder of the transaction price related to the Europe Agreement includes $23.9 million of variable consideration from estimated future co-development billing and is expected to be recognized over the remaining development service period.

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

		Three Months Ended June 30,				Six Months Ended June 30,
Agreement	Performance Obligation	2018		2017 *		2018		2017 *
U.S. / RoW and China	License revenue	$	—	$	—	$	—	$	—
	Development revenue		23,479		25,167		50,202		49,923
	China performance obligation	$	—	$	—	$	—	$	—

*	Recast to reflect the adoption of the new revenue standards. See Note 1.

The transaction price related to consideration received and accounts receivable has been allocated to each of the following performance obligations under the U.S./RoW Agreement and China Agreement, along with any associated deferred revenue as follows (in thousands):

U.S. / RoW and China Agreements	Cumulative Revenue Through June 30, 2018		Deferred Revenue at June 30, 2018		Total Consideration Through June 30, 2018
License	$	286,216	$	—	$	286,216
Co-development, information sharing & committee services		353,870		32,600		386,470
China performance obligation		—		115,942		115,942
Total license and development revenue	$	640,086	$	148,542	$	788,628

The revenue recognized under the U.S./RoW Agreement in the quarter ended June 30, 2018 included a reduction in revenue of $0.3 million as true-up relating to prior periods resulting from changes to estimated variable consideration in the current period. The remainder of the transaction price related to the U.S./RoW Agreement and China Agreement includes $251.3 million of variable consideration from estimated future co-development billing and is expected to be recognized over the remaining development service period, except for amounts allocated to the China performance obligation, which are expected to be recognized in a pattern consistent with estimated deliveries of the commercial drug product.

Other Revenues

Other revenues consist primarily of collagen material sold for research purposes. Other revenues were immaterial for all periods presented.

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 performance obligations. 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 performance obligations. 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

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

3.	Fair Value Measurements

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

	June 30, 2018
	Level 1		Level 2		Level 3		Total
Corporate bonds	$	—	$	28,094	$	—	$	28,094
Bond and mutual funds		10,377		—		—		10,377
Equity investments		210		—		—		210
Money market funds		580,287		—		—		580,287
Total	$	590,874	$	28,094	$	—	$	618,968

	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

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

	June 30, 2018
	Level 1		Level 2		Level 3		Total
Lease financing obligations	$	—	$	—	$	98,300	$	98,300

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

The fair values of the Company’s 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.

- 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

6 Months Ended

Jun. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Components

4.	Balance Sheet Components

Cash and Cash Equivalents

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

	June 30, 2018		December 31, 2017
Cash	$	63,516	$	103,716
Money market funds		580,287		569,942
Total cash and cash equivalents	$	643,803	$	673,658

At June 30, 2018 and December 31, 2017, a total of $24.7 million and $32.3 million, respectively, of the Company’s cash and cash equivalents were held outside of the U.S. in its foreign subsidiaries to be used primarily for its China operations.

Investments

The Company’s investments consist of available-for-sale debt investments and marketable equity investments. 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):

	June 30, 2018
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Corporate bonds	$	28,132	$	—	$	(38	)	$	28,094
Bond and mutual funds		10,341		36		—			10,377
Equity investments		126		84		—			210
Total investments	$	38,599	$	120	$	(38	)	$	38,681

	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

At June 30, 2018, all of the available-for-sale investments had contractual maturities within one year. The Company periodically reviews its available-for-sale investments for other-than-temporary impairment. The Company considers factors such as the duration, severity and the reason for the decline in value, the potential recovery period and its intent to sell. For debt securities, the Company also considers whether (i) it is more likely than not that the Company will be required to sell the debt securities before recovery of their amortized cost basis, and (ii) the amortized cost basis cannot be recovered as a result of credit losses. During the three and six months ended June 30, 2018 and 2017, the Company did not recognize any other-than-temporary impairment loss.

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	June 30, 2018		December 31, 2017
Preclinical and clinical trial accruals	$	23,893	$	32,321
Payroll and related accruals		12,631		18,810
Property taxes and other		1,843		4,201
Professional services		2,370		1,991
Other		8,755		6,458
Total accrued liabilities	$	49,492	$	63,781

Stock-Based Compensation

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

5.	Stock-Based Compensation

Stock-based compensation expense was allocated to research and development and general and administrative expense as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development	$	7,894	$	5,621	$	14,264	$	10,521
General and administrative		5,337		3,950		9,845		7,459
Total stock-based compensation expense	$	13,231	$	9,571	$	24,109	$	17,980

The assumptions used to estimate the fair value of stock options granted and purchases under the Company’s 2014 Employee Share Purchase Plan (“ESPP”) using the Black-Scholes option valuation model were as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
Stock Options
Expected term (in years)		5.4			5.4			5.4			5.7
Expected volatility		67.5	%		71.0	%		67.8	%		71.6	%
Risk-free interest rate		2.8	%		1.9	%		2.7	%		2.3	%
Expected dividend yield		—			—			—			—
Weighted average estimated fair value	$	31.35		$	17.06		$	32.12		$	16.26

ESPPs
Expected term (in years)	0.5 - 2.0			0.5 - 2.0			0.5 - 2.0			0.5 - 2.0
Expected volatility	47.3 - 75.3		%	52.8 - 77.2		%	47.3 - 75.3		%	52.8 - 77.2		%
Risk-free interest rate	0.8 - 2.6		%	0.5 - 1.3		%	0.8 - 2.6		%	0.5 - 1.3		%
Expected dividend yield		—			—			—			—
Weighted average estimated fair value	$	15.25		$	9.10		$	13.67		$	8.98

Income Taxes

6 Months Ended

Jun. 30, 2018

Income Tax Disclosure [Abstract]

Income Taxes

6.	Income Taxes

The provisions for income taxes for the three and six months ended June 30, 2018 and 2017 were due to foreign taxes.

Based upon the weight of available evidence, which includes its historical operating performance, reported cumulative net losses since inception and expected continuing net loss, the Company has established and continues to maintain a full valuation allowance against its deferred tax assets as it does not currently believe that realization of those assets is more likely than not.

Related Party Transactions

6 Months Ended

Jun. 30, 2018

Related Party Transactions

7.	Related Party Transactions

Astellas is an equity investor in the Company and considered a related party. The Company recorded revenue related to collaboration agreements with Astellas of $20.5 million and $5.1 million during the three months ended June 30, 2018 and 2017, respectively, and $25.6 million and $9.8 million during the six months ended June 30, 2018 and 2017, respectively. The related party revenue for the three and six months ended June 30, 2018 included $14.9 million of a $15.0 million regulatory milestone under the Japan Agreement that was included in the transaction price during the second quarter of 2018. See Note 2 and below for details. The related party revenue was recast for the three and six months ended June 30, 2017 as a result of adoption of the new revenue standards. See Note 1 for details.

The Company recorded expense related to collaboration agreements with Astellas of $0.2 million and $0.3 million during the three months ended June 30, 2018 and 2017, respectively, and $0.7 million and $0.5 million during the six months ended June 30, 2018 and 2017, respectively.

As of June 30, 2018 and December 31, 2017, accounts receivable from Astellas were $25.9 million and $4.0 million, respectively, and amounts due to Astellas were $0.3 million and $0.3 million, respectively. The accounts receivable from Astellas as of June 30, 2018 included $20.9 million related to a sale of roxadustat API to Astellas during the second quarter of 2018. The sale was made pursuant to a material transfer agreement in anticipation of the execution of an amendment to the Japan Agreement allowing Astellas to manufacture roxadustat drug product, which is expected to be finalized in the third quarter of 2018. The sale enables Astellas to conduct the commercial scale manufacturing validation for roxadustat drug product in anticipation of commercial launch in Japan. The associated consideration was recorded as deferred revenue because Astellas’ right to use the material was limited as of June 30, 2018.

Prepaid expenses and other current assets as of June 30, 2018 included $15.0 million of contract assets related to a regulatory milestone under the Japan Agreement with Astellas associated with NDA submission in Japan. See Note 2 for details. According to the Japan Agreement, this amount is not billable to Astellas until the submission of NDA, therefore it was included in the prepaid expenses and other current assets on the Company’s condensed consolidated balance sheet as of June 30, 2018.

Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Description of Operations

Basis of Presentation and Principles of Consolidation

Revenue Recognition

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

Investments

Use of Estimates

Recently Issued and Adopted Accounting Guidance

New Revenue Standards

	Three Months Ended June 30, 2017									Six Months Ended June 30, 2017
	As Previously Reported			New Revenue Standards Adjustment			As Recast			As Previously Reported			New Revenue Standards Adjustment			As Recast
Statement of Operations
License revenue	$	21,352		$	(21,352	)	$	—		$	40,933		$	(40,933	)	$	—
Development and other revenue		7,645			22,623			30,268			14,955			44,755			59,710
Total revenue		28,997			1,271			30,268			55,888			3,822			59,710
Net loss		(33,183	)		1,271			(31,912	)		(66,344	)		3,822			(62,522	)
Net loss per share - basic and diluted	$	(0.48	)	$	0.02		$	(0.46	)	$	(0.99	)	$	0.05		$	(0.94	)

										December 31, 2017
										As Previously Reported			New Revenue Standards Adjustment			As Recast
Balance Sheet
Deferred revenue, current										$	7,968		$	8,702		$	16,670
Deferred revenue, net of current											112,231			26,010			138,241
Accumulated deficit											(595,945	)		(34,712	)		(630,657	)

ASU 2016-01

	Accumulated Other Comprehensive Loss			Accumulated Deficit
Balance at December 31, 2017	$	(1,795	)	$	(630,657	)	*
Impact of change in accounting principle upon adoption of ASU 2016-01		(1,250	)		1,250
Opening balance as of January 1, 2018	$	(3,045	)	$	(629,407	)

*	Recast to reflect the adoption of the new revenue standards. See above.

The adoption of this guidance had no impact to the Company’s condensed consolidated statement of operations or condensed consolidated statement of cash flows for the six months ended June 30, 2018.

ASU 2017-09

ASU 2016-16

Recently Issued Accounting Guidance Not Yet Adopted

Collaboration Arrangements

Accounting for the Astellas Agreements

The promised services that were analyzed, along with their general timing of satisfaction and recognition as revenue, are as follows:

(1)

(2)

(3)	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 promises are generally satisfied throughout the term of the agreements.

(4)	Manufacturing of clinical supplies of products. This promise 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.

(5)	Committee service. This promise is satisfied throughout the course of the agreements as meetings are attended.

(6)

Accounting for the AstraZeneca Agreements

1.	While the two agreements were largely negotiated separately, those negotiations proceeded concurrently, and were intended to be completed contemporaneously, presuming AstraZeneca decided to proceed with licenses in all regions available.

Promised services that were not distinct have been combined with other promised services to form a distinct bundle of promised services, with revenue being recognized on the bundle of services rather than the individual promised services. There are no right-of-return provisions for the delivered items in the AstraZeneca agreements.

U.S./RoW Agreement:

The promised services that were analyzed, along with their general timing of satisfaction and recognition as revenue, are as follows:

(1)

(2)

(3)	Manufacturing of clinical supplies of products. This promise 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.

(4)	Information sharing and committee service. These promises are satisfied throughout the course of the agreement as services are provided.

(5)

China Agreement:

The performance obligation that were analyzed, along with their general timing of satisfaction and recognition as revenue, are as follows:

•

Other Revenues

Other revenues consist primarily of collagen material sold for research purposes. Other revenues were immaterial for all periods presented.

Deferred Revenue

Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Schedule of Adoption of New Revenue Standards

	Three Months Ended June 30, 2017									Six Months Ended June 30, 2017
	As Previously Reported			New Revenue Standards Adjustment			As Recast			As Previously Reported			New Revenue Standards Adjustment			As Recast
Statement of Operations
License revenue	$	21,352		$	(21,352	)	$	—		$	40,933		$	(40,933	)	$	—
Development and other revenue		7,645			22,623			30,268			14,955			44,755			59,710
Total revenue		28,997			1,271			30,268			55,888			3,822			59,710
Net loss		(33,183	)		1,271			(31,912	)		(66,344	)		3,822			(62,522	)
Net loss per share - basic and diluted	$	(0.48	)	$	0.02		$	(0.46	)	$	(0.99	)	$	0.05		$	(0.94	)

										December 31, 2017
										As Previously Reported			New Revenue Standards Adjustment			As Recast
Balance Sheet
Deferred revenue, current										$	7,968		$	8,702		$	16,670
Deferred revenue, net of current											112,231			26,010			138,241
Accumulated deficit											(595,945	)		(34,712	)		(630,657	)

Schedule of Impacts to Accumulated Other Comprehensive Loss and Accumulated Deficit Upon Adoption of Guidance

The impacts to the Company’s accumulated other comprehensive loss and accumulated deficit upon adoption of this guidance are as follows (in thousands):

	Accumulated Other Comprehensive Loss			Accumulated Deficit
Balance at December 31, 2017	$	(1,795	)	$	(630,657	)	*
Impact of change in accounting principle upon adoption of ASU 2016-01		(1,250	)		1,250
Opening balance as of January 1, 2018	$	(3,045	)	$	(629,407	)

*	Recast to reflect the adoption of the new revenue standards. See above.

Collaboration Agreements (Tables)

6 Months Ended

Jun. 30, 2018

Japan [Member]

Summary of Revenue Recognized under Agreement

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

		Three Months Ended June 30,				Six Months Ended June 30,
Agreement	Performance Obligation	2018		2017 *		2018		2017 *
Japan	License revenue	$	14,323	$	—	$	14,323	$	—
	Development revenue	$	1,142	$	317	$	1,591	$	613

*	Recast to reflect the adoption of the new revenue standards. See Note 1.

Transaction Price Related to Consideration Received and Accounts Receivable Allocated to Performance Obligations along with Associated Deferred Revenue

Japan Agreement	Cumulative Revenue Through June 30, 2018		Deferred Revenue at June 30, 2018		Total Consideration Through June 30, 2018
License	$	74,089	$	—	$	74,089
Manufacturing--clinical supplies		13,099		473		13,572
Total license and development revenue	$	87,188	$	473	$	87,661

Europe [Member]

Summary of Revenue Recognized under Agreement

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

		Three Months Ended June 30,				Six Months Ended June 30,
Agreement	Performance Obligation	2018		2017 *		2018		2017 *
Europe	License revenue	$	—	$	—	$	—	$	—
	Development revenue	$	5,003	$	4,781	$	9,726	$	9,171

*	Recast to reflect the adoption of the new revenue standards. See Note 1.

Transaction Price Related to Consideration Received and Accounts Receivable Allocated to Performance Obligations along with Associated Deferred Revenue

Europe Agreement	Cumulative Revenue Through June 30, 2018		Deferred Revenue at June 30, 2018		Total Consideration Through June 30, 2018
License	$	370,481	$	—	$	370,481
Manufacturing--clinical supplies		194,059		5,337		199,396
Total license and development revenue	$	564,540	$	5,337	$	569,877

U.S./RoW and China [Member]

Summary of Revenue Recognized under Agreement

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

		Three Months Ended June 30,				Six Months Ended June 30,
Agreement	Performance Obligation	2018		2017 *		2018		2017 *
U.S. / RoW and China	License revenue	$	—	$	—	$	—	$	—
	Development revenue		23,479		25,167		50,202		49,923
	China performance obligation	$	—	$	—	$	—	$	—

*	Recast to reflect the adoption of the new revenue standards. See Note 1.

Transaction Price Related to Consideration Received and Accounts Receivable Allocated to Performance Obligations along with Associated Deferred Revenue

U.S. / RoW and China Agreements	Cumulative Revenue Through June 30, 2018		Deferred Revenue at June 30, 2018		Total Consideration Through June 30, 2018
License	$	286,216	$	—	$	286,216
Co-development, information sharing & committee services		353,870		32,600		386,470
China performance obligation		—		115,942		115,942
Total license and development revenue	$	640,086	$	148,542	$	788,628

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

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):

	June 30, 2018
	Level 1		Level 2		Level 3		Total
Corporate bonds	$	—	$	28,094	$	—	$	28,094
Bond and mutual funds		10,377		—		—		10,377
Equity investments		210		—		—		210
Money market funds		580,287		—		—		580,287
Total	$	590,874	$	28,094	$	—	$	618,968

	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

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):

	June 30, 2018
	Level 1		Level 2		Level 3		Total
Lease financing obligations	$	—	$	—	$	98,300	$	98,300

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

Balance Sheet Components (Tables)

6 Months Ended

Jun. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Cash and Cash Equivalents

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

	June 30, 2018		December 31, 2017
Cash	$	63,516	$	103,716
Money market funds		580,287		569,942
Total cash and cash equivalents	$	643,803	$	673,658

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

	June 30, 2018
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Corporate bonds	$	28,132	$	—	$	(38	)	$	28,094
Bond and mutual funds		10,341		36		—			10,377
Equity investments		126		84		—			210
Total investments	$	38,599	$	120	$	(38	)	$	38,681

	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

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	June 30, 2018		December 31, 2017
Preclinical and clinical trial accruals	$	23,893	$	32,321
Payroll and related accruals		12,631		18,810
Property taxes and other		1,843		4,201
Professional services		2,370		1,991
Other		8,755		6,458
Total accrued liabilities	$	49,492	$	63,781

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Allocated Stock-Based Compensation Expense

Stock-based compensation expense was allocated to research and development and general and administrative expense as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development	$	7,894	$	5,621	$	14,264	$	10,521
General and administrative		5,337		3,950		9,845		7,459
Total stock-based compensation expense	$	13,231	$	9,571	$	24,109	$	17,980

Schedule of Assumptions used to Estimate Fair Value of Stock Options Granted and Purchases under 2014 Employee Share Purchase Plan

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
Stock Options
Expected term (in years)		5.4			5.4			5.4			5.7
Expected volatility		67.5	%		71.0	%		67.8	%		71.6	%
Risk-free interest rate		2.8	%		1.9	%		2.7	%		2.3	%
Expected dividend yield		—			—			—			—
Weighted average estimated fair value	$	31.35		$	17.06		$	32.12		$	16.26

ESPPs
Expected term (in years)	0.5 - 2.0			0.5 - 2.0			0.5 - 2.0			0.5 - 2.0
Expected volatility	47.3 - 75.3		%	52.8 - 77.2		%	47.3 - 75.3		%	52.8 - 77.2		%
Risk-free interest rate	0.8 - 2.6		%	0.5 - 1.3		%	0.8 - 2.6		%	0.5 - 1.3		%
Expected dividend yield		—			—			—			—
Weighted average estimated fair value	$	15.25		$	9.10		$	13.67		$	8.98

Significant Accounting Policies - Additional Information (Detail) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018 Segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2016 USD ($)
Accounting Policy [Line Items]
Number of operating segment \| Segment	1
Short term investments Maturity	12 months
Long term Investments Maturity	12 months
U.S. federal statutory income tax rate	21.00%	35.00%
ASU 2014-09 [Member] \| Accumulated Deficit [Member]
Accounting Policy [Line Items]
Increase in accumulative deficit				$ 43.7
New Revenue Standards [Member] \| Revenue [Member]
Accounting Policy [Line Items]
Increase (reduction) in revenue		$ 5.3	$ 3.6

Significant Accounting Policies - Schedule of Adoption of New Revenue Standards (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Statement of Operations
Total revenue	$ 43,952	$ 30,268	$ 75,876	$ 59,710
Net loss	$ (23,420)	$ (31,912)	$ (64,817)	$ (62,522)
Net loss per share - basic and diluted	$ (0.28)	$ (0.46)	$ (0.78)	$ (0.94)
Balance Sheet
Deferred revenue	$ 37,845		$ 37,845		$ 16,670
Deferred revenue, net of current	137,436		137,436		138,241
Accumulated deficit	(694,224)		(694,224)		(630,657)
License Revenue [Member]
Statement of Operations
Total revenue	14,323	$ 0	14,323	$ 0
Development and Other Revenue [Member]
Statement of Operations
Total revenue	$ 29,629	30,268	$ 61,553	59,710
As Previously Reported [Member] \| ASU 2014-09 [Member]
Statement of Operations
Total revenue		28,997		55,888
Net loss		$ (33,183)		$ (66,344)
Net loss per share - basic and diluted		$ (0.48)		$ (0.99)
Balance Sheet
Deferred revenue					7,968
Deferred revenue, net of current					112,231
Accumulated deficit					(595,945)
As Previously Reported [Member] \| License Revenue [Member] \| ASU 2014-09 [Member]
Statement of Operations
Total revenue		$ 21,352		$ 40,933
As Previously Reported [Member] \| Development and Other Revenue [Member] \| ASU 2014-09 [Member]
Statement of Operations
Total revenue		7,645		14,955
New Revenue Standards Adjustment [Member] \| ASU 2014-09 [Member]
Statement of Operations
Total revenue		1,271		3,822
Net loss		$ 1,271		$ 3,822
Net loss per share - basic and diluted		$ 0.02		$ 0.05
Balance Sheet
Deferred revenue					8,702
Deferred revenue, net of current					26,010
Accumulated deficit					$ (34,712)
New Revenue Standards Adjustment [Member] \| License Revenue [Member] \| ASU 2014-09 [Member]
Statement of Operations
Total revenue		$ (21,352)		$ (40,933)
New Revenue Standards Adjustment [Member] \| Development and Other Revenue [Member] \| ASU 2014-09 [Member]
Statement of Operations
Total revenue		$ 22,623		$ 44,755

Summary of Significant Accounting Policies - Schedule of Impacts to Accumulated Other Comprehensive Loss and Accumulated Deficit Upon Adoption of Guidance (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Accounting Policy [Line Items]
Accumulated other comprehensive loss	$ (2,611)		$ (1,795)
Accumulated deficit	$ (694,224)		$ (630,657)
ASU 2016-01 [Member]
Accounting Policy [Line Items]
Accumulated other comprehensive loss		$ (3,045)
Accumulated deficit		(629,407)
Impact of change in accounting principle upon adoption of ASU 2016-01 [Member] \| ASU 2016-01 [Member]
Accounting Policy [Line Items]
Accumulated other comprehensive loss		(1,250)
Accumulated deficit		$ 1,250

Collaboration Agreements - Astellas Agreements - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended	6 Months Ended	12 Months Ended		35 Months Ended	45 Months Ended
	Jul. 31, 2016	Apr. 30, 2006	Jun. 30, 2005	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2012	Dec. 31, 2010	Feb. 28, 2009	Feb. 28, 2009	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue				$ 37,845	$ 37,845					$ 16,670
Astellas Agreement [Member] \| Japan [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received									$ 40,100
Potential milestone payments			$ 132,500
Commercial sales milestone			15,000
Milestones revenue	$ 22,500
Consideration associated with milestone included in transaction price				15,000
Changes in revenue due to prior period adjustment				14,900	14,900
Deferred revenue				$ 20,900	20,900
Astellas Agreement [Member] \| Japan [Member] \| Clinical and Development Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments			22,500
Astellas Agreement [Member] \| Japan [Member] \| Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments			$ 95,000
Astellas Agreement [Member] \| Europe [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent and time-based payments received								$ 320,000
Potential milestone payments		$ 425,000
Changes in revenue due to prior period adjustment					$ (200)
Clinical development milestones						$ 50,000	$ 40,000
Percentage of joint development costs committed to fund		50.00%
Additional consideration based on net sales description					Low 20% range
Astellas Agreement [Member] \| Europe [Member] \| Clinical and Development Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments		$ 90,000
Astellas Agreement [Member] \| Europe [Member] \| Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments		$ 335,000

Collaboration Agreements - AstraZeneca Agreements - Additional Information 1 (Detail) - AstraZeneca Agreements [Member] - USD ($) $ in Millions		3 Months Ended		6 Months Ended	12 Months Ended
	Jul. 30, 2013	Sep. 30, 2017	Dec. 31, 2015	Jun. 30, 2018	Dec. 31, 2015
U.S./RoW [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront, non-contingent, non-refundable and time-based payments	$ 374.0
Potential milestone payments	875.0
Commercial sales milestone	325.0
Shared development costs			$ 233.0
Additional consideration based on net sales description				Low 20% range
U.S./RoW [Member] \| FibroGen, Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Shared development costs			$ 116.5
U.S./RoW [Member] \| Clinical and Development Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments	65.0
U.S./RoW [Member] \| Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments	325.0
U.S./RoW [Member] \| Deferred Approval Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments	160.0
U.S./RoW [Member] \| Development Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receipt of development milestone payment					$ 15.0
China [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments	348.5
Proceeds from upfront, non-contingent and non-refundable payments	28.2
Commercial sales and other events milestone	187.5
Milestone payment, revenue recognition		$ 15.0
China [Member] \| Clinical and Development Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments	15.0
China [Member] \| Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments	$ 146.0

Collaboration Agreements - Accounting for the Astellas Agreements - Additional Information 2 (Detail) - Astellas Agreement [Member]	6 Months Ended
	Jun. 30, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Co-development services, currently estimated continuation year	2019
Manufacturing Commercial Supplies of Products [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Manufacturing commercial supplies of products, revenue recognized	$ 0
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%
Japan [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-contingent upfront payments received	$ 40,100,000
Variable consideration related to payments for milestones considered probable of being achieved	37,500,000
Variable consideration related to co-development billings	12,700,000
Provision for co-development services	0
Europe [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-contingent upfront payments received	320,000,000
Variable consideration related to payments for milestones considered probable of being achieved	90,000,000
Variable consideration related to co-development billings	$ 183,800,000

Collaboration Agreements - Accounting for the AstraZeneca Agreements - Additional Information 3 (Detail) - AstraZeneca Agreements [Member]	6 Months Ended
	Jun. 30, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Right-of-return provisions for delivered items	$ 0
Royalty rate against projected net revenues	40.00%
Discount rate applied	17.50%
Co-development services, currently estimated continuation year	2020
Manufacturing Commercial Supplies of Products [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Manufacturing commercial supplies of products, revenue recognized	$ 0
U.S./RoW and China [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-contingent upfront payments received	402,200,000
Variable consideration related to payments for milestones considered probable of being achieved	30,000,000
Variable consideration related to co-development billings	$ 673,000,000

Collaboration Agreements - Summary of Revenue Recognized under Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	$ 43,952	$ 30,268	$ 75,876	$ 59,710
License Revenue [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	14,323	0	14,323	0
Development and Other Revenue [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	29,629	30,268	61,553	59,710
Astellas Agreement [Member] \| License Revenue [Member] \| Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	14,323	0	14,323	0
Astellas Agreement [Member] \| License Revenue [Member] \| Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	0	0	0	0
Astellas Agreement [Member] \| Development and Other Revenue [Member] \| Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	1,142	317	1,591	613
Astellas Agreement [Member] \| Development and Other Revenue [Member] \| Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	5,003	4,781	9,726	9,171
AstraZeneca Agreements [Member] \| China [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	0	0	0	0
AstraZeneca Agreements [Member] \| License Revenue [Member] \| U.S./RoW [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	0	0	0	0
AstraZeneca Agreements [Member] \| Development and Other Revenue [Member] \| U.S./RoW [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue	$ 23,479	$ 25,167	$ 50,202	$ 49,923

Collaboration Agreements - Transaction Price Related to Consideration Received and Accounts Receivable Allocated to Performance Obligations along with Associated Deferred Revenue (Detail) $ in Thousands	Jun. 30, 2018 USD ($)
Astellas Agreement [Member] \| Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	$ 87,188
Deferred Revenue	473
Total Consideration	87,661
Astellas Agreement [Member] \| Japan [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	74,089
Deferred Revenue	0
Total Consideration	74,089
Astellas Agreement [Member] \| Japan [Member] \| Manufacturing-clinical supplies [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	13,099
Deferred Revenue	473
Total Consideration	13,572
Astellas Agreement [Member] \| Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	564,540
Deferred Revenue	5,337
Total Consideration	569,877
Astellas Agreement [Member] \| Europe [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	370,481
Deferred Revenue	0
Total Consideration	370,481
Astellas Agreement [Member] \| Europe [Member] \| Manufacturing-clinical supplies [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	194,059
Deferred Revenue	5,337
Total Consideration	199,396
AstraZeneca Agreements [Member] \| U.S./RoW and China [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	640,086
Deferred Revenue	148,542
Total Consideration	788,628
AstraZeneca Agreements [Member] \| U.S./RoW and China [Member] \| License [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	286,216
Deferred Revenue	0
Total Consideration	286,216
AstraZeneca Agreements [Member] \| U.S./RoW and China [Member] \| Co-development, information sharing & committee services [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	353,870
Deferred Revenue	32,600
Total Consideration	386,470
AstraZeneca Agreements [Member] \| U.S./RoW and China [Member] \| China performance obligation [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative Revenue	0
Deferred Revenue	115,942
Total Consideration	$ 115,942

Collaboration Agreements - Summary of Revenue Recognized Under the Collaboration Agreements - Additional Information 4 (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Remainder of transaction price, variable consideration from estimated future co-development billing		$ 2.6
Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Remainder of transaction price, variable consideration from estimated future co-development billing		23.9
U.S./RoW and China [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Remainder of transaction price, variable consideration from estimated future co-development billing		251.3
Astellas Agreement [Member] \| Japan [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Changes in revenue due to prior period adjustment	$ 14.9	14.9
Astellas Agreement [Member] \| Europe [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Changes in revenue due to prior period adjustment		(0.2)
AstraZeneca Agreements [Member] \| U.S./RoW and China [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Changes in revenue due to prior period adjustment		$ (0.3)

Fair Value Measurements - Fair Values of Financial Liabilities Carried at Historical Cost (Detail) - Lease financing obligations [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value disclosure	$ 98,300	$ 98,476
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	$ 98,300	$ 98,476

Fair Value Measurements - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Transfers of assets from level 1 to 2	$ 0	$ 0
Transfers of assets from level 2 to 1	0	0
Transfers of liabilities from level 1 to 2	0	0
Transfers of liabilities from level 2 to 1	0	0
Transfers of assets into level 3	0	0
Transfers of assets out of level 3	0	0
Transfers of liabilities into level 3	0	0
Transfers of liabilities out of level 3	$ 0	$ 0

Balance Sheet Components - Schedule of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Cash And Cash Equivalents [Abstract]
Cash	$ 63,516	$ 103,716
Money market funds	580,287	569,942
Total cash and cash equivalents	$ 643,803	$ 673,658

Balance Sheet Components - Additional Information (Detail) - USD ($)		3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 643,803,000	$ 643,803,000		$ 643,803,000		$ 673,658,000
Contractual maturities of available-for-sale investments	1 year
Other-than-temporary impairment loss		0	$ 0	0	$ 0
Foreign subsidiaries [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 24,700,000	$ 24,700,000		$ 24,700,000		$ 32,300,000

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	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 38,599	$ 71,360
Gross Unrealized Holding Gains	120	1,252
Gross Unrealized Holding Losses	(38)	(46)
Fair Value	38,681	72,566
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,132	53,985
Gross Unrealized Holding Gains	0	4
Gross Unrealized Holding Losses	(38)	(46)
Fair Value	28,094	53,943
Bond and mutual funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,341	17,249
Gross Unrealized Holding Gains	36	1,153
Gross Unrealized Holding Losses	0	0
Fair Value	10,377	18,402
Equity investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	126	126
Gross Unrealized Holding Gains	84	95
Gross Unrealized Holding Losses	0	0
Fair Value	$ 210	$ 221

Balance Sheet Components - Schedule of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accrued Liabilities Current [Abstract]
Preclinical and clinical trial accruals	$ 23,893	$ 32,321
Payroll and related accruals	12,631	18,810
Property taxes and other	1,843	4,201
Professional services	2,370	1,991
Other	8,755	6,458
Total accrued liabilities	$ 49,492	$ 63,781

Stock-Based Compensation - Schedule of Allocated Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 13,231	$ 9,571	$ 24,109	$ 17,980
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	7,894	5,621	14,264	10,521
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 5,337	$ 3,950	$ 9,845	$ 7,459

Stock-Based Compensation - Schedule of Assumptions used to Estimate Fair Value of Stock Options Granted and Purchases under 2014 Employee Share Purchase Plan (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 4 months 24 days	5 years 4 months 24 days	5 years 4 months 24 days	5 years 8 months 12 days
Expected volatility	67.50%	71.00%	67.80%	71.60%
Risk-free interest rate	2.80%	1.90%	2.70%	2.30%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Weighted average estimated fair value	$ 31.35	$ 17.06	$ 32.12	$ 16.26
2014 Employee Share Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	47.30%	52.80%	47.30%	52.80%
Expected volatility, maximum	75.30%	77.20%	75.30%	77.20%
Risk-free interest rate, minimum	0.80%	0.50%	0.80%	0.50%
Risk-free interest rate, maximum	2.60%	1.30%	2.60%	1.30%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Weighted average estimated fair value	$ 15.25	$ 9.10	$ 13.67	$ 8.98
2014 Employee Share Purchase Plan [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	6 months	6 months
2014 Employee Share Purchase Plan [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	2 years	2 years	2 years	2 years

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Accounts receivable from related party	$ 25,886		$ 25,886		$ 4,004
Accrued liabilities to related party	327		327		272
Prepaid expenses and other current assets from related party	15,000		15,000		0
Astellas Agreement [Member] \| Japan [Member]
Related Party Transaction [Line Items]
Prepaid expenses and other current assets from related party	15,000		15,000
Astellas [Member] \| Collaborative Arrangement [Member]
Related Party Transaction [Line Items]
Revenue related to collaboration agreements	20,500	$ 5,100	25,600	$ 9,800
Expense related to collaboration agreements	200	$ 300	700	$ 500
Accounts receivable from related party	25,900		25,900		4,000
Accrued liabilities to related party	300		300		$ 300
Astellas [Member] \| Astellas Agreement [Member] \| API Shipment [Member]
Related Party Transaction [Line Items]
Accrued liabilities to related party	20,900		20,900
Unbilled Revenues [Member] \| Astellas [Member] \| Regulatory Milestone [Member]
Related Party Transaction [Line Items]
Revenue related to collaboration agreements	$ 14,900		$ 15,000

Fair Value Measurements - Fair Values of Financial Assets Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	$ 38,681	$ 72,566
Corporate bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	28,094	53,943
Bond and mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	10,377	18,402
Equity investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	210	221
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of financial assets	618,968	642,508
Fair Value, Measurements, Recurring [Member] \| Corporate bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	28,094	53,943
Fair Value, Measurements, Recurring [Member] \| Bond and mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	10,377	18,402
Fair Value, Measurements, Recurring [Member] \| Equity investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	210	221
Fair Value, Measurements, Recurring [Member] \| Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value disclosure	580,287	569,942
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of financial assets	590,874	588,565
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Corporate bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Bond and mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	10,377	18,402
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Equity investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	210	221
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value disclosure	580,287	569,942
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of financial assets	28,094	53,943
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Corporate bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	28,094	53,943
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Bond and mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Equity investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value disclosure	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of financial assets	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Corporate bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Bond and mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Equity investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value disclosure	$ 0	$ 0