Five Prime Therapeutics (FPRX) 10-Q 8 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 01, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	FPRX
Entity Registrant Name	FIVE PRIME THERAPEUTICS INC
Entity Central Index Key	1,175,505
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		35,209,289

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 65,941	$ 59,790
Marketable securities	323,485	232,900
Receivables from collaborative partners	4,269	13,133
Prepaid and other current assets	9,348	5,367
Total current assets	403,043	311,190
Restricted cash	1,543	1,543
Property and equipment, net	30,290	30,762
Other long-term assets	1,838	552
Total assets	436,714	344,047
Current liabilities:
Accounts payable	1,831	2,237
Accrued personnel-related expenses	4,188	7,156
Other accrued liabilities	29,348	27,519
Deferred revenue, current portion	4,443	12,713
Deferred rent, current portion	1,356	1,356
Total current liabilities	41,166	50,981
Deferred revenue, long-term portion	14,816	10,223
Deferred rent, long-term portion	18,266	17,641
Other long-term liabilities	250
Stockholders' equity:
Common stock, $0.001 par value; 100,000,000 shares authorized, 35,265,857 issued and 34,334,645 outstanding at March 31, 2018. 28,982,056 issued and 28,178,639 outstanding at December 31, 2017	34	28
Preferred stock, $0.001 par value, 10,000,000 shares authorized; no shares issued and outstanding
Additional paid-in capital	537,391	421,257
Accumulated other comprehensive loss	(586)	(476)
Accumulated deficit	(174,623)	(155,607)
Total stockholders' equity	362,216	265,202
Total liabilities and stockholders' equity	$ 436,714	$ 344,047

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	35,265,857	28,982,056
Common stock, shares outstanding	34,334,645	28,178,639
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Collaboration revenue	$ 32,486	$ 10,135
Operating expenses:
Research and development	43,552	33,760
General and administrative	10,478	10,486
Total operating expenses	54,030	44,246
Loss from operations	(21,544)	(34,111)
Interest and other income, net	1,159	668
Other loss, net	(5)
Loss before income tax	(20,390)	(33,443)
Net loss	$ (20,390)	$ (33,443)
Basic and diluted net loss per common share	$ (0.63)	$ (1.21)
Weighted-average shares used to compute basic and diluted net loss per common share	32,314	27,657

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (20,390)	$ (33,443)
Other comprehensive loss:
Unrealized loss on marketable securities	(110)	(205)
Comprehensive loss	$ (20,500)	$ (33,648)

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net loss	$ (20,390)	$ (33,443)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,151	515
Stock-based compensation expense	7,820	9,887
Amortization of premiums and discounts on marketable securities	13	708
Loss on disposal of property and equipment	5
Changes in operating assets and liabilities:
Receivables from collaborative partners	8,864	(1,950)
Income tax receivable		(7)
Prepaid, other current assets, and other long-term assets	(5,267)	1,453
Accounts payable	(406)	473
Accrued personnel-related expenses	(2,968)	(4,279)
Deferred revenue	(2,304)	(3,183)
Deferred rent	625	(216)
Other accrued liabilities and other long-term liabilities	2,235	2,113
Net cash used in operating activities	(10,622)	(27,929)
Investing activities
Purchases of marketable securities	(153,957)	(125,701)
Maturities of marketable securities	63,250	205,750
Purchases of property and equipment	(840)	(1,824)
Net cash (used in) provided by investing activities	(91,547)	78,225
Financing activities
Proceeds from public offering of common stock, net	107,613
Proceeds from exercise of stock options	1,704	1,048
Repurchase of shares to satisfy tax withholding obligations	(997)	(11,813)
Net cash provided by (used in) financing activities	108,320	(10,765)
Net increase in cash and cash equivalents and restricted cash	6,151	39,531
Cash, cash equivalents and restricted cash at beginning of period	61,333	9,196
Cash, cash equivalents and restricted cash at end of period	67,484	48,727
Supplemental schedule of noncash investing activities
Unpaid property and equipment included in accrued liabilities	531	1,548
Supplemental cash flow information
Cash and cash equivalents at beginning of period	59,790	7,653
Restricted cash at beginning of period	1,543	1,543
Cash, cash equivalents and restricted cash at beginning of period	61,333	9,196
Cash and cash equivalents at end of period	65,941	47,184
Restricted cash at end of period	1,543	1,543
Cash, cash equivalents and restricted cash at end of period	$ 67,484	$ 48,727

Description of Business

Description of Business	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Description of Business	1. Description of Business Five Prime Therapeutics, Inc. (we, us, our, or the company) is a clinical-stage biotechnology company focused on discovering and developing innovative protein therapeutics. We were incorporated in December 2001 in Delaware. Our operations are based in South San Francisco, California and we operate in one segment. Unaudited Interim Financial Information The accompanying financial information as of March 31, 2018 is unaudited. The condensed financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of our financial condition at the date of the interim balance sheet. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying condensed financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2017, or our Annual Report, filed with the U.S. Securities and Exchange Commission, or the SEC, on February 27, 2018, as amended by our Annual Report on Form 10-K/A, as filed with the SEC on March 12, 2018, or, collectively our Annual Report.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ materially from those estimates. Restricted Cash Restricted cash consists of a certificate of deposit held by our bank as collateral for a standby letter of credit in the same notional amount by our landlord to secure our obligations under our corporate office and laboratory facility lease that we entered into in December 2016. We are required to maintain this restricted cash balance for the duration of this lease, the amount of which is subject to reduction starting on January 1, 2023, if certain conditions are met. Fair Value of Financial Instruments We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. We do not have any assets or liabilities measured using Level 3 inputs as of March 31, 2018. The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): March 31, 2018 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 19,119 $ 19,119 $ — $ — U.S. Treasury securities 309,415 309,415 — — Corporate bonds 15,183 — 15,183 — Commercial paper 31,523 — 31,523 — Certificate of deposit 1,543 — 1,543 — Total $ 376,783 $ 328,534 $ 48,249 $ — December 31, 2017 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 31,802 $ 31,802 $ — $ — U.S. Treasury securities 232,900 232,900 — — Certificate of deposit 1,543 — 1,543 — Total $ 266,245 $ 264,702 $ 1,543 $ — Revenue Recognition Effective January 1, 2018, we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , or Topic 606, The terms of our collaborative research and development agreements include up-front and license fees, research funding, milestone and other contingent payments to us for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of commercialized products. Arrangements that include up-front payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until we perform obligations under these arrangements. We record research funding payable to us as accounts receivable when our right to consideration is unconditional. The event-based milestone payments represent variable consideration, and we use the most likely amount method to estimate this variable consideration. Given the high degree of uncertainty around achievement of these milestones, we determine the milestone amounts to be fully constrained and do not recognize revenue until the uncertainty associated with these payments is resolved. We will recognize revenue from sales-based royalty payments when or as the sales occur. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. A performance obligation is a promise in a contract to transfer a distinct good or service to our collaborative partners and is the unit of account in Topic 606. A contract’s transaction price is allocated to each distinct performance obligation based on relative standalone selling price and recognized as revenue when, or as, the performance obligation is satisfied. Under Topic 606, we elected to use the practical expedients permitted related to adoption, which do not require us to disclose certain information regarding our remaining performance obligations as of the end of the reporting period. Topic 606 is applicable for revenue recognized in accordance with the p Net Loss Per Share of Common Stock We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. We excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands): Three Months Ended March 31, 2018 2017 Options to purchase common stock 4,032 3,711 Restricted stock awards (RSAs) 829 1,047 4,861 4,758 Accounting Pronouncements Adopted in 2018 In May 2014, the Financial Accounting Standards Board, or FASB, issued Topic 606, which supersedes nearly all existing revenue recognition guidance under GAAP. The FASB subsequently issued amendments to Topic 606 that have the same effective date and transition date. The core principle of Topic 606 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. Topic 606 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing GAAP, including identifying performance obligations in a contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. We adopted this new guidance, effective January 1, 2018, using the modified retrospective transition method, in which the standard is applied as of the date of initial adoption. We recorded the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings. The adoption of the new revenue recognition guidance resulted in a decrease of $1.4 million to deferred revenue and an increase of $1.4 million to retained earnings as of January 1, 2018. We determined that the classification between deferred revenue, current portion, and deferred revenue, long-term portion, will change from the adoption of Topic 606. We concluded that we will classify deferred revenue for all licensing and collaboration arrangements as deferred revenue, long-term and reclassified to deferred revenue, current when the remaining term of the estimated performance period is one year or less. Our adoption of Topic 606 on January 1, 2018 affected the following financial statement line items: Condensed Statements of Operations Three Months ended March 31, 2018 (in thousands, except per share data) Under Topic 606 Under Topic 605 Effect of change Collaboration and license revenue $ 32,486 $ 33,693 $ (1,207 ) Operating expenses 54,030 54,030 — Operating loss $ (21,544 ) $ (20,337 ) $ (1,207 ) Net loss $ (20,390 ) $ (19,183 ) $ (1,207 ) Net loss per share applicable to common stockholders - basic and diluted $ (0.63 ) $ (0.59 ) $ (0.04 ) Condensed Balance Sheets As of March 31, 2018 (in thousands) Under Topic 606 Under Topic 605 Effect of change Receivable from collaborative partner $ 4,269 $ 4,269 $ — Deferred revenue, current portion 4,443 11,773 (7,330 ) Deferred revenue, long-term portion 14,816 7,652 7,164 Accumulated deficit (174,623 ) (174,789 ) 166 Condensed Statements of Cash Flows Three Months ended March 31, 2018 (in thousands) Under Topic 606 Under Topic 605 Effect of change Net loss $ (20,390 ) $ (19,183 ) $ (1,207 ) Decrease in deferred revenue in connection with Topic 606 adoption 1,373 — 1,373 Changes in operating assets and liabilities Receivable from collaborative partner 8,864 8,864 — Deferred revenue (3,677 ) (3,511 ) (166 ) Cash, cash equivalents and restricted cash at beginning of period 61,333 61,333 — Cash, cash equivalents and restricted cash at end of period 67,484 67,484 — In May 2017, FASB issued ASU 2017-09 Compensation-Stock Compensation (Topic 718) – Scope of Modification Accounting In November 2016, FASB issued ASU 2016-18 Statement of Cash Flows (Topic 230) – Restricted Cash Accounting Pronouncements Not Yet Adopted In February 2016, FASB issued ASU 2016-02 Leases (Topic 842) all annual and interim reporting periods thereafter. E

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	3 Months Ended
	Mar. 31, 2018
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	3. Cash Equivalents and Marketable Securities The following table summarizes our cash equivalents and marketable securities (in thousands): March 31, 2018 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 19,119 $ — $ — $ 19,119 U.S. Treasury securities 309,997 — (582 ) 309,415 Corporate bonds 15,184 1 (2 ) 15,183 Commercial paper 31,526 4 (7 ) 31,523 Total cash equivalents and marketable securities 375,826 5 (591 ) 375,240 Less: cash equivalents (51,751 ) (5 ) 1 (51,755 ) Total marketable securities $ 324,075 $ — $ (590 ) $ 323,485 December 31, 2017 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 31,802 $ — $ — $ 31,802 U.S. Treasury securities 233,376 — (476 ) 232,900 Total cash equivalents and marketable securities 265,178 — (476 ) 264,702 Less: cash equivalents (31,802 ) — — (31,802 ) Total marketable securities $ 233,376 $ — $ (476 ) $ 232,900 As of March 31, 2018, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Debt securities maturing: In one year or less $ 304,214 $ 303,652 In one to two years 19,861 19,833 Total marketable securities $ 324,075 $ 323,485 We determined that the gross unrealized losses on our marketable securities as of March 31, 2018 were temporary in nature. We currently do not intend to sell these securities prior to maturity and do not consider these investments to be other-than-temporarily impaired at March 31, 2018. There were no sales of available-for-sale securities in any of the periods presented.

Equity Incentive Plans

Equity Incentive Plans	3 Months Ended
	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plans	4. Equity Incentive Plans The following table summarizes option activity under our equity incentive plans and related information: Options Outstanding Weighted Weighted Average Average Remaining Number of Exercise Price Contractual Shares Per Share Term (years) Balance at December 31, 2017 3,867,645 $ 30.35 Options granted 527,850 $ 18.72 Options exercised (182,820 ) $ 9.32 Options forfeited (19,775 ) $ 38.30 Options expired (134,705 ) $ 36.60 Balance at March 31, 2018 4,058,195 $ 29.54 7.26 Options exercisable at March 31, 2018 1,897,326 $ 24.42 6.05 We have granted restricted stock awards, or RSAs, to certain of our employees, some of which are subject to performance conditions. RSAs are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting and are not forfeitable once fully vested. We based the fair value of RSAs on the closing sale price of our common stock on the grant date. For awards subject to performance conditions, we recognize stock-based compensation expense using the accelerated attribution recognition method when it is probable that the performance condition will be achieved. The following table summarizes RSA activity under our 2013 Omnibus Incentive Plan and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at December 31, 2017 803,417 $ 40.24 RSAs granted 274,250 $ 18.82 RSAs vested (128,359 ) $ 42.29 RSAs forfeited (18,096 ) $ 36.13 Unvested balance at March 31, 2018 931,212 $ 33.73 As of March 31, 2018, there were 1,894,733 shares of common stock available for future issuance under our 2013 Omnibus Incentive Plan. Stock-Based Compensation Total stock-based compensation expense recognized was as follows (in thousands): Three Months Ended March 31, 2018 2017 Research and development $ 3,934 $ 5,286 General and administrative $ 3,886 $ 4,601 Total $ 7,820 $ 9,887 We estimated the fair value of stock options using the Black-Scholes option-pricing model based on the date of grant of the applicable stock option with the following assumptions: Three Months Ended March 31, 2018 2017 Expected term (years) 6.0-6.3 6.0-6.3 Expected volatility 70% 68% Risk-free interest rate 2.6% 2.1% Expected dividend yield 0% 0% As of March 31, 2018, we had $43.7 million of total unrecognized compensation expense related to unvested employee and director stock options that we expect to recognize over a weighted-average period of 2.7 years. Additionally, we had $24.4 million of total unrecognized compensation expense related to employee and director RSAs that we expect to recognize over a weighted-average period of 2.1 years.

License and Collaboration Arran

License and Collaboration Arrangements	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Arrangements	5. License and Collaboration Arrangements See Note 9 to the audited consolidated financial statements included in Part V, Item 15 of our Annual Report for information on our license and collaboration agreements. The following table presents changes during the three months ended March 31, 2018 in the balances of our contract assets, including receivables from collaborative partners, and contract liabilities, including deferred revenue, as compared to what we disclosed in our Annual Report. (in thousands) Contract Assets Balance at December 31, 2017 $ 13,133 Additions 30,296 Deductions (39,160 ) Balance at March 31, 2018 $ 4,269 (in thousands) Contract Liabilities Balance at December 31, 2017 $ 22,936 Additions for advanced billings 1,015 Deductions for performance obligations satisfied in current period (3,319 ) Deductions for performance obligations satisfied in previous periods in connection with Topic 606 adoption (1,373 ) Balance at March 31, 2018 $ 19,259 Bristol-Myers Squibb Company Immuno-Oncology Research Collaboration In March 2014, we entered into a research collaboration and license agreement, or the immuno-oncology research collaboration, with Bristol-Myers Squibb Company, or BMS. We identified one performance obligation under the immuno-oncology research collaboration with BMS for the research license to access our technology, the exclusive commercial license and research activities. BMS’ options to select additional collaboration targets are not priced at a discount and therefore do not represent performance obligations for which the transaction price would be allocated. The transaction price includes the $20.0 million non-refundable up-front fee, $13.7 million of research funding and $2.4 million of equity premium. We concluded that the transaction price should not include the variable consideration related to maintenance fees and unachieved clinical and regulatory development milestones as they were considered to be constrained as it is probable that the inclusion of such variable consideration could result in a significant reversal in revenue in the future. We will recognize any consideration related to sales-based milestones (including royalties) when the related sales occur, as we have determined that these amounts relate predominantly to the license granted and therefore will be recognized on the later to occur of satisfaction of the performance obligation, or the occurrence of the related sales. We will re-evaluate the transaction price at each reporting period. For the three months ended March 31, 2018, no adjustments were made to the transaction price. Upon adoption of Topic 606, we recognized an additional $0.7 million of revenue, through a decrease to deferred revenue and an increase to beginning retained earnings, based on the difference between the input method currently used under Topic 606 and the ratable recognition previously used under Topic 605. Under the input method, we recognize revenue on the basis of our efforts or inputs applicable to the satisfaction of a performance obligation (e.g., resources consumed, labor hours expended, costs incurred, or time elapsed) relative to the total expected inputs applicable to the satisfaction of that performance obligation. We concluded that we will recognize revenue based on actual costs incurred as a percentage of total budgeted costs as we complete our performance obligation. Revenue allocated to the performance obligation, $1.6 million, was recognized under Topic 606 for the three months ended March 31, 2018. Through March 31, 2018, we had recognized $30.1 million of the transaction price as collaboration revenue under the agreement. The remaining transaction price of $6.0 million will be recognized as revenue under the input method over the estimated performance period. License and Collaboration Agreement In October 2015, we entered into a license and collaboration agreement, or the cabiralizumab collaboration agreement, with BMS. The cabiralizumab collaboration agreement supersedes the clinical trial collaboration agreement we entered into with BMS in November 2014, or the original collaboration agreement. We assessed the two agreements separately as standalone agreements under Topic 606. Under the original collaboration agreement, we identified one performance obligation for the execution of Phase 1a/1 clinical trial of cabiralizumab in combination with Opdivo® (nivolumab) We used the input method to measure progress toward completion of the performance obligation and concluded that we will recognize revenue based on actual costs incurred for clinical research organizations, or CROs, and laboratory services as a percentage of total budgeted costs as we complete our performance obligation. We will recognize revenue from reimbursements when we have the right to invoice BMS. No adjustment was necessary upon adoption of Topic 606. We recognized $1.4 million of revenue allocated to the performance obligation under Topic 606 for the three months ended March 31, 2018. Total revenue recognized for the quarter, including progress made toward the performance obligation and reimbursements, was $4.5 million. Through March 31, 2018, we recognized $19.6 million of the transaction price as collaboration revenue under the agreement. The remaining transaction price of $10.4 million is recorded in deferred revenue as of March 31, 2018 and will be recognized as revenue under the input method over the estimated performance period. Under the cabiralizumab collaboration agreement, we identified the following performance obligations: (1) license to BMS; and (2) transfer of licensed know-how to BMS. The transaction price consists of the $350.0 million non-refundable up-front fee. We concluded that the transaction price should not yet include the milestone payments as they are fully constrained. We will recognize any consideration related to sales-based milestones (including royalties) when the related sales occur, as we have determined that these amounts relate predominantly to the license granted and therefore are recognized on the later to occur of satisfaction of the performance obligation, or occurrence of the related sales. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three months ended March 31, 2018, no adjustments were made to the transaction price. The $350.0 million non-refundable up-front fee was fully recognized concurrent with the transfer of the license and know-how in 2015. Opdivo® (nivolumab) Zai Lab China License and Collaboration Agreement In December 2017, we entered into a license and collaboration agreement, or the China collaboration agreement, with Zai Lab (Shanghai) Co., Ltd., or Zai Lab, pursuant to which we granted Zai Lab an exclusive license to develop and commercialize bemarituzumab in China, Hong Kong, Macau and Taiwan, each a region, and collectively, the territory. We evaluated the China collaboration agreement under Topic 606. Based on that evaluation, we identified the following performance obligations: (1) license grant to Zai Lab along with the transfer of licensed know-how, development drug supply and global development activities; (2) commercial drug supply; and (3) development of companion diagnostics. The $5.0 million non-refundable up-front fee, net of value-added tax and other withholdings of $0.8 million and the $8.3 million of expected reimbursement from Zai Lab for global development activities are included as part of the transaction price. We determined the $8.3 million of expected reimbursements from Zai Lab based on the probability-weighted amounts of a range of possible consideration amounts. We have not included the clinical and regulatory development milestone payments in the transaction price as all such milestone amounts are fully constrained. We will recognize any consideration related to sales-based milestones (including royalties) when the related sales occur, as we determined that these amounts relate predominantly to the license granted and therefore will be recognized on the later to occur of satisfaction of the performance obligation, or the occurrence of related sales. Zai Lab’s option to purchase commercial drug supply from us represents a material right and we will include the additional consideration to us for such supply in the transaction price as Zai’s payment obligations for such supply become due under the commercial supply agreement we and Zai Lab would enter into. We concluded that the reimbursement of costs incurred for the development of companion diagnostics qualifies for t We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three months ended March 31, 2018, no adjustments were made to the transaction price. We use the input method to measure progress toward completion of the performance obligation for the license grant, transfer of licensed know-how, development drug supply and global development activities. We concluded that revenue will be recognized based on actual costs incurred for CROs as a percentage of total budgeted costs as we complete our performance obligation. We will recognize revenue from reimbursements for commercial drug supply and for the development of companion diagnostics when we have the right to invoice Zai Lab. No adjustment was necessary upon adoption of Topic 606. For the three months ended March 31, 2018, revenue for the first performance obligation was $0.3 million. Total revenue recognized for the third performance obligation during the quarter was $0.9 million. Of the remaining transaction price of $12.2 million, $4.4 million is recorded in deferred revenue and will be recognized over the estimated performance period for satisfaction of the performance obligation. $7.8 million of the transaction price will be recorded in deferred revenue when invoiced as global development activities are incurred. GlaxoSmithKline LLC Respiratory Diseases and Muscle Diseases Collaborations In April 2012, we entered into a research collaboration and license agreement, or the respiratory diseases collaboration, with GlaxoSmithKline LLC, or GSK, to identify new therapeutic approaches to treat refractory asthma and chronic obstructive pulmonary disease, or COPD, with a particular focus on identifying novel protein therapeutics and antibody targets. In January 2016, we amended our respiratory diseases collaboration to extend the research term by three months to July 2016 to allow additional validation of the protein targets we discovered and to increase the research funding. In July 2010, we entered into a research collaboration and license agreement, or the muscle diseases collaboration with GSK, to identify potential drug targets and drug candidates to treat skeletal muscle diseases. We conducted three customized cell-based screens and one in vivo We assessed the respiratory diseases collaboration and muscle diseases collaboration in accordance with Topic 606. Based on that assessment, we identified the one performance obligation under each collaboration for the research license and research activities. The non-refundable up-front fees and the equity premiums are included as part of the transaction prices for each collaboration. We will include the . The clinical and regulatory development milestone payments have not been included in the transaction prices, as all such milestone amounts are fully constrained. We will recognize any consideration related to sales-based milestones, including royalties when the related sales occur, as we have determined that these amounts relate predominantly to the license granted and therefore will be recognized on the later to occur of satisfaction of the performance obligation or the related sales. Under the respiratory diseases collaboration, GSK’s option to add research funding were also not included in the transaction price. As the expired in April 2018, we are no longer eligible to receive milestone payments or royalties under that agreement. We will re-evaluate the transaction price for the respiratory diseases collaboration in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three months ended March 31, 2018, no adjustments were made to the transaction prices of the collaborations with GSK. Under the respiratory diseases collaboration and the muscle diseases collaboration, the non-refundable up-front fees, the equity premiums and the payment for research activities were fully recognized in 2016 and 2014, respectively. UCB Fibrosis and CNS Collaboration In March 2013, we entered into a research collaboration and license agreement, or the fibrosis and CNS collaboration, with UCB Pharma, S.A., or UCB, to identify potential biologics targets and therapeutics in the areas of fibrosis-related immunologic diseases and central nervous system disorders. We assessed the fibrosis and CNS collaboration under Topic 606. Based on that assessment, we identified research activities as our only performance obligation. UCB’s options to select additional collaboration targets and to license exclusive rights to selected targets are not priced at a discount and therefore do not represent performance obligations for which the transaction price would be allocated. The transaction price includes the $6.0 million non-refundable up-front fee, the $6.6 million technology access fee, the $1.0 million reimbursement for reagent costs and the $2.0 million of research funding. We have not included the clinical and regulatory development milestone payments in the transaction price as all such milestone amounts are fully constrained. We will recognize any consideration related to sales-based milestones, including royalties, when the related sales occur, as we have determined that these amounts relate predominantly to the license granted and therefore will be recognized on the later to occur of satisfaction of the performance obligation or the related sales. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three months ended March 31, 2018, there was no change in the transaction price. Upon adoption of Topic 606, we recognized an additional $0.6 million of revenue, through a decrease to deferred revenue and an increase to beginning retained earnings, based on the difference between the input method currently used under Topic 606 and the ratable recognition previously used under Topic 605. We use the input method to measure progress toward completion of the performance obligation and concluded that revenue will be recognized based on actual full time equivalent labor hours expended as a percentage of total budgeted costs. The $0.6 million adjustment recorded upon the adoption of Topic 606 recognized the remainder of the transaction price. In March 2018, UCB triggered a $0.3 million milestone payment to us upon selection of an undisclosed confirmed target for further development.

Summary of Significant Accoun12

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ materially from those estimates.
Restricted Cash	Restricted Cash Restricted cash consists of a certificate of deposit held by our bank as collateral for a standby letter of credit in the same notional amount by our landlord to secure our obligations under our corporate office and laboratory facility lease that we entered into in December 2016. We are required to maintain this restricted cash balance for the duration of this lease, the amount of which is subject to reduction starting on January 1, 2023, if certain conditions are met.
Fair Value of Financial Instruments	Fair Value of Financial Instruments We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. We do not have any assets or liabilities measured using Level 3 inputs as of March 31, 2018. The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): March 31, 2018 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 19,119 $ 19,119 $ — $ — U.S. Treasury securities 309,415 309,415 — — Corporate bonds 15,183 — 15,183 — Commercial paper 31,523 — 31,523 — Certificate of deposit 1,543 — 1,543 — Total $ 376,783 $ 328,534 $ 48,249 $ — December 31, 2017 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 31,802 $ 31,802 $ — $ — U.S. Treasury securities 232,900 232,900 — — Certificate of deposit 1,543 — 1,543 — Total $ 266,245 $ 264,702 $ 1,543 $ —
Revenue Recognition	Revenue Recognition Effective January 1, 2018, we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , or Topic 606, The terms of our collaborative research and development agreements include up-front and license fees, research funding, milestone and other contingent payments to us for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of commercialized products. Arrangements that include up-front payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until we perform obligations under these arrangements. We record research funding payable to us as accounts receivable when our right to consideration is unconditional. The event-based milestone payments represent variable consideration, and we use the most likely amount method to estimate this variable consideration. Given the high degree of uncertainty around achievement of these milestones, we determine the milestone amounts to be fully constrained and do not recognize revenue until the uncertainty associated with these payments is resolved. We will recognize revenue from sales-based royalty payments when or as the sales occur. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. A performance obligation is a promise in a contract to transfer a distinct good or service to our collaborative partners and is the unit of account in Topic 606. A contract’s transaction price is allocated to each distinct performance obligation based on relative standalone selling price and recognized as revenue when, or as, the performance obligation is satisfied. Under Topic 606, we elected to use the practical expedients permitted related to adoption, which do not require us to disclose certain information regarding our remaining performance obligations as of the end of the reporting period. Topic 606 is applicable for revenue recognized in accordance with the p
Net Loss Per Share of Common Stock	Net Loss Per Share of Common Stock We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. We excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands): Three Months Ended March 31, 2018 2017 Options to purchase common stock 4,032 3,711 Restricted stock awards (RSAs) 829 1,047 4,861 4,758
Accounting Pronouncements Adopted in 2018	Accounting Pronouncements Adopted in 2018 In May 2014, the Financial Accounting Standards Board, or FASB, issued Topic 606, which supersedes nearly all existing revenue recognition guidance under GAAP. The FASB subsequently issued amendments to Topic 606 that have the same effective date and transition date. The core principle of Topic 606 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. Topic 606 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing GAAP, including identifying performance obligations in a contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. We adopted this new guidance, effective January 1, 2018, using the modified retrospective transition method, in which the standard is applied as of the date of initial adoption. We recorded the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings. The adoption of the new revenue recognition guidance resulted in a decrease of $1.4 million to deferred revenue and an increase of $1.4 million to retained earnings as of January 1, 2018. We determined that the classification between deferred revenue, current portion, and deferred revenue, long-term portion, will change from the adoption of Topic 606. We concluded that we will classify deferred revenue for all licensing and collaboration arrangements as deferred revenue, long-term and reclassified to deferred revenue, current when the remaining term of the estimated performance period is one year or less. Our adoption of Topic 606 on January 1, 2018 affected the following financial statement line items: Condensed Statements of Operations Three Months ended March 31, 2018 (in thousands, except per share data) Under Topic 606 Under Topic 605 Effect of change Collaboration and license revenue $ 32,486 $ 33,693 $ (1,207 ) Operating expenses 54,030 54,030 — Operating loss $ (21,544 ) $ (20,337 ) $ (1,207 ) Net loss $ (20,390 ) $ (19,183 ) $ (1,207 ) Net loss per share applicable to common stockholders - basic and diluted $ (0.63 ) $ (0.59 ) $ (0.04 ) Condensed Balance Sheets As of March 31, 2018 (in thousands) Under Topic 606 Under Topic 605 Effect of change Receivable from collaborative partner $ 4,269 $ 4,269 $ — Deferred revenue, current portion 4,443 11,773 (7,330 ) Deferred revenue, long-term portion 14,816 7,652 7,164 Accumulated deficit (174,623 ) (174,789 ) 166 Condensed Statements of Cash Flows Three Months ended March 31, 2018 (in thousands) Under Topic 606 Under Topic 605 Effect of change Net loss $ (20,390 ) $ (19,183 ) $ (1,207 ) Decrease in deferred revenue in connection with Topic 606 adoption 1,373 — 1,373 Changes in operating assets and liabilities Receivable from collaborative partner 8,864 8,864 — Deferred revenue (3,677 ) (3,511 ) (166 ) Cash, cash equivalents and restricted cash at beginning of period 61,333 61,333 — Cash, cash equivalents and restricted cash at end of period 67,484 67,484 — In May 2017, FASB issued ASU 2017-09 Compensation-Stock Compensation (Topic 718) – Scope of Modification Accounting In November 2016, FASB issued ASU 2016-18 Statement of Cash Flows (Topic 230) – Restricted Cash
Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Not Yet Adopted In February 2016, FASB issued ASU 2016-02 Leases (Topic 842) all annual and interim reporting periods thereafter. E

Summary of Significant Accoun13

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Summary of Financial Instruments Measured at Fair Value	The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): March 31, 2018 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 19,119 $ 19,119 $ — $ — U.S. Treasury securities 309,415 309,415 — — Corporate bonds 15,183 — 15,183 — Commercial paper 31,523 — 31,523 — Certificate of deposit 1,543 — 1,543 — Total $ 376,783 $ 328,534 $ 48,249 $ — December 31, 2017 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 31,802 $ 31,802 $ — $ — U.S. Treasury securities 232,900 232,900 — — Certificate of deposit 1,543 — 1,543 — Total $ 266,245 $ 264,702 $ 1,543 $ —
Securities Excluded from Calculation of Diluted Net Loss Per Share	We excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands): Three Months Ended March 31, 2018 2017 Options to purchase common stock 4,032 3,711 Restricted stock awards (RSAs) 829 1,047 4,861 4,758
ASU 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Summary of Guidance Effect under Topic 605 before Adoption of Topic 606 on Financial Statement	Our adoption of Topic 606 on January 1, 2018 affected the following financial statement line items: Condensed Statements of Operations Three Months ended March 31, 2018 (in thousands, except per share data) Under Topic 606 Under Topic 605 Effect of change Collaboration and license revenue $ 32,486 $ 33,693 $ (1,207 ) Operating expenses 54,030 54,030 — Operating loss $ (21,544 ) $ (20,337 ) $ (1,207 ) Net loss $ (20,390 ) $ (19,183 ) $ (1,207 ) Net loss per share applicable to common stockholders - basic and diluted $ (0.63 ) $ (0.59 ) $ (0.04 ) Condensed Balance Sheets As of March 31, 2018 (in thousands) Under Topic 606 Under Topic 605 Effect of change Receivable from collaborative partner $ 4,269 $ 4,269 $ — Deferred revenue, current portion 4,443 11,773 (7,330 ) Deferred revenue, long-term portion 14,816 7,652 7,164 Accumulated deficit (174,623 ) (174,789 ) 166 Condensed Statements of Cash Flows Three Months ended March 31, 2018 (in thousands) Under Topic 606 Under Topic 605 Effect of change Net loss $ (20,390 ) $ (19,183 ) $ (1,207 ) Decrease in deferred revenue in connection with Topic 606 adoption 1,373 — 1,373 Changes in operating assets and liabilities Receivable from collaborative partner 8,864 8,864 — Deferred revenue (3,677 ) (3,511 ) (166 ) Cash, cash equivalents and restricted cash at beginning of period 61,333 61,333 — Cash, cash equivalents and restricted cash at end of period 67,484 67,484 —

Cash Equivalents and Marketab14

Cash Equivalents and Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2018
Cash And Cash Equivalents [Abstract]
Summary of Cash Equivalents and Marketable Securities	The following table summarizes our cash equivalents and marketable securities (in thousands): March 31, 2018 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 19,119 $ — $ — $ 19,119 U.S. Treasury securities 309,997 — (582 ) 309,415 Corporate bonds 15,184 1 (2 ) 15,183 Commercial paper 31,526 4 (7 ) 31,523 Total cash equivalents and marketable securities 375,826 5 (591 ) 375,240 Less: cash equivalents (51,751 ) (5 ) 1 (51,755 ) Total marketable securities $ 324,075 $ — $ (590 ) $ 323,485 December 31, 2017 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 31,802 $ — $ — $ 31,802 U.S. Treasury securities 233,376 — (476 ) 232,900 Total cash equivalents and marketable securities 265,178 — (476 ) 264,702 Less: cash equivalents (31,802 ) — — (31,802 ) Total marketable securities $ 233,376 $ — $ (476 ) $ 232,900
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	As of March 31, 2018, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Debt securities maturing: In one year or less $ 304,214 $ 303,652 In one to two years 19,861 19,833 Total marketable securities $ 324,075 $ 323,485

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Option Activity under Equity Incentive Plans and Related Information	The following table summarizes option activity under our equity incentive plans and related information: Options Outstanding Weighted Weighted Average Average Remaining Number of Exercise Price Contractual Shares Per Share Term (years) Balance at December 31, 2017 3,867,645 $ 30.35 Options granted 527,850 $ 18.72 Options exercised (182,820 ) $ 9.32 Options forfeited (19,775 ) $ 38.30 Options expired (134,705 ) $ 36.60 Balance at March 31, 2018 4,058,195 $ 29.54 7.26 Options exercisable at March 31, 2018 1,897,326 $ 24.42 6.05
Schedule of Restricted Stock Award Activity under 2013 Omnibus Incentive Plan and Related Information	The following table summarizes RSA activity under our 2013 Omnibus Incentive Plan and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at December 31, 2017 803,417 $ 40.24 RSAs granted 274,250 $ 18.82 RSAs vested (128,359 ) $ 42.29 RSAs forfeited (18,096 ) $ 36.13 Unvested balance at March 31, 2018 931,212 $ 33.73
Schedule of Stock-Based Compensation Expenses Recognized	Total stock-based compensation expense recognized was as follows (in thousands) Three Months Ended March 31, 2018 2017 Research and development $ 3,934 $ 5,286 General and administrative $ 3,886 $ 4,601 Total $ 7,820 $ 9,887
Schedule of Stock Options Weighted-Average Assumptions	We estimated the fair value of stock options using the Black-Scholes option-pricing model based on the date of grant of the applicable stock option with the following assumptions: Three Months Ended March 31, 2018 2017 Expected term (years) 6.0-6.3 6.0-6.3 Expected volatility 70% 68% Risk-free interest rate 2.6% 2.1% Expected dividend yield 0% 0%

License and Collaboration Arr16

License and Collaboration Arrangements (Tables)	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Changes in Balances of Contract Assets and Contract Liabilities	The following table presents changes during the three months ended March 31, 2018 in the balances of our contract assets, including receivables from collaborative partners, and contract liabilities, including deferred revenue, as compared to what we disclosed in our Annual Report. (in thousands) Contract Assets Balance at December 31, 2017 $ 13,133 Additions 30,296 Deductions (39,160 ) Balance at March 31, 2018 $ 4,269 (in thousands) Contract Liabilities Balance at December 31, 2017 $ 22,936 Additions for advanced billings 1,015 Deductions for performance obligations satisfied in current period (3,319 ) Deductions for performance obligations satisfied in previous periods in connection with Topic 606 adoption (1,373 ) Balance at March 31, 2018 $ 19,259

Description of Business - Addit

Description of Business - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment	1

Summary of Significant Accoun18

Summary of Significant Accounting Policies - Summary of Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Total	$ 376,783	$ 266,245
Money market funds [Member]
Assets
Cash equivalents	19,119	31,802
Corporate bonds [Member]
Assets
Cash equivalents	15,183
Commercial paper [Member]
Assets
Cash equivalents	31,523
Certificate of deposit [Member]
Assets
Cash equivalents	1,543	1,543
Level 1 [Member]
Assets
Total	328,534	264,702
Level 1 [Member] | Money market funds [Member]
Assets
Cash equivalents	19,119	31,802
Level 2 [Member]
Assets
Total	48,249	1,543
Level 2 [Member] | Corporate bonds [Member]
Assets
Cash equivalents	15,183
Level 2 [Member] | Commercial paper [Member]
Assets
Cash equivalents	31,523
Level 2 [Member] | Certificate of deposit [Member]
Assets
Cash equivalents	1,543	1,543
U.S. Treasury securities [Member]
Assets
U.S. Treasury securities	309,415	232,900
U.S. Treasury securities [Member] | Level 1 [Member]
Assets
U.S. Treasury securities	$ 309,415	$ 232,900

Summary of Significant Accoun19

Summary of Significant Accounting Policies - Securities Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	4,861	4,758
Options to purchase common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	4,032	3,711
Restricted stock awards (RSAs) [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	829	1,047

Summary of Significant Accoun20

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Jan. 01, 2018	Mar. 31, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Increase to retained earnings		$ (174,623)	$ (155,607)
ASU 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Increase to retained earnings	$ 1,400	$ 166
Decrease to deferred revenue	$ 1,400

Summary of Significant Accoun21

Summary of Significant Accounting Policies - Summary of Guidance Effect under Topic 605 before Adoption of Topic 606 on Condensed Statements of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Collaboration and license revenue	$ 32,486
Operating expenses	54,030	$ 44,246
Operating loss	(21,544)	(34,111)
Net loss	$ (20,390)	$ (33,443)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.63)	$ (1.21)
ASU 2014-09 [Member] | Under Topic 605 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Collaboration and license revenue	$ 33,693
Operating expenses	54,030
Operating loss	(20,337)
Net loss	$ (19,183)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.59)
ASU 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Collaboration and license revenue	$ (1,207)
Operating loss	(1,207)
Net loss	$ (1,207)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.04)

Summary of Significant Accoun22

Summary of Significant Accounting Policies - Summary of Guidance Effect under Topic 605 before Adoption of Topic 606 on Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Receivable from collaborative partner	$ 4,269		$ 13,133
Deferred revenue, current portion	4,443		12,713
Deferred revenue, long-term portion	14,816		10,223
Accumulated deficit	(174,623)		$ (155,607)
ASU 2014-09 [Member] | Under Topic 605 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Receivable from collaborative partner	4,269
Deferred revenue, current portion	11,773
Deferred revenue, long-term portion	7,652
Accumulated deficit	(174,789)
ASU 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred revenue, current portion	(7,330)
Deferred revenue, long-term portion	7,164
Accumulated deficit	$ 166	$ 1,400

Summary of Significant Accoun23

Summary of Significant Accounting Policies - Summary of Guidance Effect under Topic 605 before Adoption of Topic 606 on Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net loss	$ (20,390)	$ (33,443)
Decrease in deferred revenue in connection with Topic 606 adoption	1,373
Changes in operating assets and liabilities:
Receivables from collaborative partners	8,864	(1,950)
Deferred revenue	(3,677)
Cash, cash equivalents and restricted cash at beginning of period	61,333	9,196
Cash, cash equivalents and restricted cash at end of period	67,484	$ 48,727
ASU 2014-09 [Member] | Under Topic 605 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net loss	(19,183)
Changes in operating assets and liabilities:
Receivables from collaborative partners	8,864
Deferred revenue	(3,511)
Cash, cash equivalents and restricted cash at beginning of period	61,333
Cash, cash equivalents and restricted cash at end of period	67,484
ASU 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net loss	(1,207)
Decrease in deferred revenue in connection with Topic 606 adoption	1,373
Changes in operating assets and liabilities:
Deferred revenue	$ (166)

Cash Equivalents and Marketab24

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 324,075	$ 233,376
Unrealized Losses	(590)	(476)
Estimated Fair Value	323,485	232,900
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	19,119	31,802
Estimated Fair Value	19,119	31,802
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	309,997	233,376
Unrealized Losses	(582)	(476)
Estimated Fair Value	309,415	232,900
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	15,184
Unrealized Gains	1
Unrealized Losses	(2)
Estimated Fair Value	15,183
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	31,526
Unrealized Gains	4
Unrealized Losses	(7)
Estimated Fair Value	31,523
Total cash equivalents and marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	375,826	265,178
Unrealized Gains	5
Unrealized Losses	(591)	(476)
Estimated Fair Value	375,240	264,702
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	(51,751)	(31,802)
Unrealized Gains	(5)
Unrealized Losses	1
Estimated Fair Value	(51,755)	$ (31,802)
Unrealized Gains	$ 5

Cash Equivalents and Marketab25

Cash Equivalents and Marketable Securities - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available For Sale Securities Debt Maturities [Abstract]
Amortized Cost, In one year or less	$ 304,214
Amortized Cost, In one to two years	19,861
Amortized Cost Basis	324,075	$ 233,376
Estimated Fair Value, In one year or less	303,652
Estimated Fair Value, In one to two years	19,833
Total marketable securities, Estimated Fair Value	$ 323,485	$ 232,900

Cash Equivalents and Marketab26

Cash Equivalents and Marketable Securities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018USD ($)
Investments Debt And Equity Securities [Abstract]
Sales of available-for-sale securities	$ 0

Equity Incentive Plans - Schedu

Equity Incentive Plans - Schedule of Option Activity under Equity Incentive Plans and Related Information (Detail)	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance | shares	3,867,645
Number of Shares, Options granted | shares	527,850
Number of Shares, Options exercised | shares	(182,820)
Number of Shares, Options forfeited | shares	(19,775)
Number of Shares, Options expired | shares	(134,705)
Number of Shares, Ending balance | shares	4,058,195
Number of Shares, Options exercisable | shares	1,897,326
Weighted-Average Exercise Price Per Share, Options beginning balance | $ / shares	$ 30.35
Weighted-Average Exercise Price Per Share, Options granted | $ / shares	18.72
Weighted-Average Exercise Price Per Share, Options exercised | $ / shares	9.32
Weighted-Average Exercise Price Per Share, Options forfeited | $ / shares	38.30
Weighted-Average Exercise Price Per Share, Options expired | $ / shares	36.60
Weighted-Average Exercise Price Per Share, Options ending balance | $ / shares	29.54
Weighted-Average Exercise Price Per Share, Options exercisable | $ / shares	$ 24.42
Weighted-Average Remaining Contractual Terms, Options ending balance	7 years 3 months 3 days
Weighted Average Remaining Contractual Term, Options exercisable	6 years 18 days

Equity Incentive Plans - Sche28

Equity Incentive Plans - Schedule of Restricted Stock Award Activity under 2013 Omnibus Incentive Plan and Related Information (Detail) - Restricted Stock Awards [Member]	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Unvested, beginning balance | shares	803,417
Number of Shares, Granted | shares	274,250
Number of Shares, Vested | shares	(128,359)
Number of Shares, Forfeited | shares	(18,096)
Number of Shares, Unvested, Ending balance | shares	931,212
Weighted-Average Grant-Date Fair Value, Unvested, Beginning balance | $ / shares	$ 40.24
Weighted-Average Grant-Date Fair Value, Granted | $ / shares	18.82
Weighted-Average Grant-Date Fair Value, Vested | $ / shares	42.29
Weighted-Average Grant-Date Fair Value, Forfeited | $ / shares	36.13
Weighted-Average Grant-Date Fair Value, Unvested, Ending balance | $ / shares	$ 33.73

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation expense related to unvested employee and director stock options		$ 43.7
Unrecognized compensation expense expected to recognize, weighted-average period	2 years 8 months 12 days
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense expected to recognize, weighted-average period	2 years 1 month 6 days
Total unrecognized compensation expense related to employee and director RSAs		$ 24.4
2013 Omnibus Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for future issuance	1,894,733

Equity Incentive Plans - Sche30

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 7,820	$ 9,887
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	3,934	5,286
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 3,886	$ 4,601

Equity Incentive Plans - Sche31

Equity Incentive Plans - Schedule of Stock Options Assumptions (Detail) - Options [Member]	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	70.00%	68.00%
Risk-free interest rate	2.60%	2.10%
Expected dividend yield	0.00%	0.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years	6 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 3 months 18 days	6 years 3 months 18 days

License and Collaboration Arr32

License and Collaboration Arrangements - Summary of Changes in Balances of Contract Assets and Contract Liabilities (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at December 31, 2017	$ 13,133
Additions	30,296
Deductions	(39,160)
Balance at March 31, 2018	4,269
Balance at December 31, 2017	22,936
Additions for advanced billings	1,015
Deductions for performance obligations satisfied in current period	(3,319)
Balance at March 31, 2018	19,259
ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deductions for performance obligations satisfied in previous periods in connection with Topic 606 adoption	$ (1,373)

Licence and Collaboration Arran

Licence and Collaboration Arrangements - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended	30 Months Ended	49 Months Ended
	Mar. 31, 2018	Dec. 31, 2015	Mar. 31, 2018	Mar. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	$ 32,486,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	(1,207,000)
Bristol-Myers Squibb Company [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable up-front fee	30,000,000
Bristol-Myers Squibb Company [Member] | Immuno-oncology collaboration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable up-front fee	20,000,000
Equity premium	2,400,000
Adjustments to transaction price	0
Research funding received	13,700,000
Remaining transaction price recorded in deferred revenue	6,000,000		$ 6,000,000	$ 6,000,000
Bristol-Myers Squibb Company [Member] | Immuno-oncology collaboration [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized				30,100,000
Bristol-Myers Squibb Company [Member] | Immuno-oncology collaboration [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	700,000
Bristol-Myers Squibb Company [Member] | Immuno-oncology collaboration [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | ASU 2014-09 [Member] | Actual Costs Incurred as a Percentage of Total Budgeted Costs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	1,600,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable up-front fee	350,000,000
Adjustments to transaction price	0
Remaining transaction price recorded in deferred revenue	$ 10,400,000		10,400,000	10,400,000
License and collaboration agreement entered month and year	2015-10
Recognized revenue under collaboration arrangement		$ 350,000,000
Revenue recognized for milestone achieved	$ 25,000,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	4,500,000		19,600,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member] | ASU 2014-09 [Member] | Actual Costs Incurred as a Percentage of Total Budgeted Costs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	1,400,000
Zai Lab [member] | China License and Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable up-front fee	5,000,000
Adjustments to transaction price	0
Revenue recognized	900,000
Remaining transaction price recorded in deferred revenue	4,400,000		4,400,000	4,400,000
Non-refundable up-front fee, net of value-added tax and other withholdings	800,000
Expected reimbursements	8,300,000		8,300,000	8,300,000
Clinical and regulatory development milestone payments	0
Remaining transaction price	12,200,000		12,200,000	12,200,000
Transaction price will be recorded in deferred revenue when invoiced	7,800,000		$ 7,800,000	$ 7,800,000
Zai Lab [member] | China License and Collaboration Agreement [Member] | ASU 2014-09 [Member] | Actual Costs Incurred as a Percentage of Total Budgeted Costs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	$ 300,000

Licence and Collaboration Arr34

Licence and Collaboration Arrangements - Additional Information 1 (Detail) - USD ($)	1 Months Ended		3 Months Ended
	Jan. 31, 2016	Jul. 31, 2010	Mar. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized			$ 32,486,000
ASU 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized			(1,207,000)
Glaxo Smith Kline LLC [Member] | Respiratory Diseases and Muscle Diseases Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Extend research terms	3 months
Extend research date	2016-07
License agreement expiration date		2018-04
Adjustments to transaction price			0
Clinical and regulatory development milestone payments			0
UCB Pharma S.A. [Member] | Fibrosis and CNS Collaboration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Adjustments to transaction price			0
UCB Pharma S.A. [Member] | Fibrosis and CNS Collaboration [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Clinical and regulatory development milestone payments			0
Non-refundable up-front fee			6,000
Technology access fee			6,600
Research funding			2,000
Milestone paymenet received			300,000
UCB Pharma S.A. [Member] | Fibrosis and CNS Collaboration [Member] | ASU 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized			600,000
UCB Pharma S.A. [Member] | Fibrosis and CNS Collaboration [Member] | Reagent [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursements costs			$ 1,000