Five Prime Therapeutics (FPRX) 10-K 24 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2016	Feb. 17, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
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 Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		28,957,118
Entity Public Float			$ 1.1

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 7,653	$ 149,971
Marketable securities	414,095	367,495
Receivable from collaborative partners	3,959	4,054
Income tax receivable	4,670
Prepaid and other current assets	9,748	6,761
Total current assets	440,125	528,281
Restricted cash	1,543
Property and equipment, net	6,207	4,539
Deferred tax asset		15,071
Other long-term assets	406	394
Total assets	448,281	548,285
Current liabilities:
Accounts payable	334	1,894
Accrued personnel-related expenses	7,957	6,878
Other accrued liabilities	15,435	5,882
Deferred revenue, current portion	14,150	17,509
Deferred rent, current portion	865	768
Income tax payable, current portion		46,437
Total current liabilities	38,741	79,368
Deferred revenue, long-term portion	17,856	31,268
Deferred rent, long-term portion		865
Income tax payable, long-term portion		3,283
Other long-term liabilities	109	295
Commitments and Contingencies (Note 12)
Stockholders’ equity:
Common stock, $0.001 par value; 100,000,000 shares authorized, 28,550,006 issued and 27,509,077 outstanding at December 31, 2016. 27,691,756 issued and 26,116,886 outstanding at December 31, 2015.	27	26
Additional paid-in capital	396,635	372,605
Accumulated other comprehensive loss	(39)	(74)
Retained earnings (accumulated deficit)	(5,048)	60,649
Total stockholders’ equity	391,575	433,206
Total liabilities and stockholders’ equity	$ 448,281	$ 548,285

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
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	28,550,006	27,691,756
Common stock, shares outstanding	27,509,077	26,116,886

Statements of Operations

Statements of Operations - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Collaboration and license revenue	$ 30,691,000	$ 379,801,000	$ 19,231,000
Operating expenses:
Research and development	94,072,000	70,197,000	43,173,000
General and administrative	35,831,000	22,631,000	13,632,000
Total operating expenses	129,903,000	92,828,000	56,805,000
Operating income (loss)	(99,212,000)	286,973,000	(37,574,000)
Interest income	2,467,000	487,000	210,000
Other expense, net		(3,000)	(60,000)
Income (loss) before income tax	(96,745,000)	287,457,000	(37,424,000)
Income tax benefit (provision)	31,048,000	(37,810,000)	0
Net income (loss)	$ (65,697,000)	$ 249,647,000	$ (37,424,000)
Net income (loss) per share attributable to common stockholders:
Basic	$ (2.44)	$ 9.73	$ (1.79)
Diluted	$ (2.44)	$ 9.23	$ (1.79)
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders:
Basic	26,955	25,661	20,865
Diluted	26,955	27,035	20,865

Statements of Comprehensive Inc

Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (65,697)	$ 249,647	$ (37,424)
Other comprehensive gain (loss):
Unrealized gain (loss) on marketable securities, net of tax	35	(75)	(2)
Comprehensive income (loss)	$ (65,662)	$ 249,572	$ (37,426)

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Research Collaboration [Member]	Common Stock [Member]	Common Stock [Member]Research Collaboration [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Research Collaboration [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings (Accumulated Deficit) [Member]
Beginning Balance at Dec. 31, 2013	$ 58,026		$ 17		$ 209,580		$ 3	$ (151,574)
Beginning Balance, Shares at Dec. 31, 2013			16,842,134
Issuance of stock, net of issuance costs	40,099	$ 18,629	$ 3	$ 1	40,096	$ 18,628
Issuance of stock, Shares			3,450,000	994,352
Issuance of common stock under equity incentive plans and related excess tax benefits	2,459		$ 1		2,458
Issuance of common stock under equity incentive plans and related excess tax benefits, Shares			393,240
Issuance of common stock upon automatic net exercise of warrants, Shares			768
Stock-based compensation expense	3,418				3,418
Other comprehensive gain (loss)	(2)						(2)
Net income (loss)	(37,424)							(37,424)
Ending Balance at Dec. 31, 2014	85,205		$ 22		274,180		1	(188,998)
Ending Balance, Shares at Dec. 31, 2014			21,680,494
Issuance of stock, net of issuance costs	78,693		$ 3		78,690
Issuance of stock, Shares			3,829,994
Issuance of common stock under equity incentive plans and related excess tax benefits	8,269		$ 1		8,268
Issuance of common stock under equity incentive plans and related excess tax benefits, Shares			606,398
Stock-based compensation expense	11,467				11,467
Other comprehensive gain (loss)	(75)						(75)
Net income (loss)	249,647							249,647
Ending Balance at Dec. 31, 2015	$ 433,206		$ 26		372,605		(74)	60,649
Ending Balance, Shares at Dec. 31, 2015	26,116,886		26,116,886
Issuance of common stock under equity incentive plans and related excess tax benefits	$ 5,200		$ 1		5,199
Issuance of common stock under equity incentive plans and related excess tax benefits, Shares			1,730,340
Repurchase of shares to satisfy tax withholding obligations	(14,054)				(14,054)
Repurchase of shares to satisfy tax withholding obligations, Shares			(338,149)
Stock-based compensation expense	32,885				32,885
Other comprehensive gain (loss)	35						35
Net income (loss)	(65,697)							(65,697)
Ending Balance at Dec. 31, 2016	$ 391,575		$ 27		$ 396,635		$ (39)	$ (5,048)
Ending Balance, Shares at Dec. 31, 2016	27,509,077		27,509,077

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net income (loss)	$ (65,697)	$ 249,647	$ (37,424)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	1,742	1,678	1,552
Loss on disposal of property and equipment	9	3	41
Stock-based compensation expense	32,885	11,467	3,418
Amortization of premium on marketable securities	4,187	2,025	1,491
Excess tax benefits from employee equity incentive plans	3,123	3,122
Deferred income taxes	15,071	(15,071)
Changes in operating assets and liabilities:
Receivable from collaborative partners	95	(3,644)	(114)
Income tax receivable	(4,670)
Prepaid, other current assets, and other long-term assets	(2,999)	(4,782)	(579)
Restricted cash	(1,543)
Accounts payable	(1,560)	798	701
Accrued personnel-related expenses	1,079	2,260	1,661
Deferred revenue	(16,771)	(11,789)	45,530
Deferred rent	(768)	(513)	(549)
Income tax payable	(52,843)	49,720
Other accrued liabilities and other long-term liabilities	8,909	4,177	(463)
Net cash provided by (used in) operating activities	(79,751)	289,098	15,265
Investing activities
Purchases of marketable securities	(516,752)	(458,058)	(158,674)
Maturities of marketable securities	466,000	222,250	90,955
Purchases of property and equipment	(2,961)	(2,426)	(1,643)
Net cash used in investing activities	(53,713)	(238,234)	(69,362)
Financing activities
Proceeds from issuances of common stock, net of issuance costs		78,693	58,728
Proceeds from issuances of common stock under equity incentive plans	8,323	5,147	2,459
Repurchase of shares to satisfy tax withholding	(14,054)
Excess tax benefits from employee equity incentive plans	(3,123)
Deferred offering costs			16
Net cash provided by (used in) financing activities	(8,854)	83,840	61,203
Net increase (decrease) in cash and cash equivalents	(142,318)	134,704	7,106
Cash and cash equivalents at beginning of year	149,971	15,267	8,161
Cash and cash equivalents at end of year	7,653	$ 149,971	15,267
Supplemental cash flow information
Cash paid for income taxes	11,433
Supplemental schedule of noncash investing and financing activities
Unpaid property and equipment purchases included in accrued liabilities	$ 1,232
Accrued and deferred offering costs			$ 144

Business

Business	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Business	1. 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.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
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 accounting principles generally accepted in the United States of America 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. Cash and Cash Equivalents We consider all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Cash equivalents are stated at fair value. 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 entered in December 2016. We are required to maintain this restricted cash balance for the duration of the lease, which amount is subject to reduction starting in the sixth year of the lease if certain conditions are met. See Note 13 for further discussion on our lease. Marketable Securities All marketable securities have been classified as “available-for-sale” and are carried at fair value, based upon quoted market prices. We consider our available-for-sale portfolio as available for use in current operations. Accordingly, we classify certain investments as short-term marketable securities, even though the stated maturity date may be one year or more beyond the current balance sheet date. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive income or loss and reported as a separate component of stockholders’ equity or deficit until realized. Realized gains and losses and declines in value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense), net. The cost of securities sold is based on the specific-identification method. We adjust the amortized cost of securities for amortization of premiums and accretion of discounts to maturity. We include interest on short-term investments in interest income. In accordance with our investment policy, management invests to diversify credit risk and only invests in debt securities with high credit quality, including U.S. government securities, and does not invest in mortgage-backed securities or mortgage loans. We periodically evaluate whether declines in the fair value of our investments below their cost are other than temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether we have the intent to sell the securities, and whether it is more likely than not that we will be required to sell the securities before the recovery of their amortized cost basis. If we determine that the decline in fair value of an investment is below its accounting basis and this decline is other than temporary, we would reduce the carrying value of the security we hold and record a loss for the amount of such decline. We have not recorded any realized losses or declines in value judged to be other than temporary on our investments in debt securities. Concentrations of Credit Risk Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash and cash equivalents and marketable securities. Cash and cash equivalents and marketable securities are invested through banks and other financial institutions in the United States. Such deposits in the United States may be in excess of insured limits. 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. For our marketable securities, we review trading activity and pricing as of the measurement date. When sufficient quoted pricing for identical securities is not available, we use market pricing and other observable market inputs for similar securities obtained from various third-party data providers. These inputs either represent quoted prices for similar assets in active markets or have been derived from observable market data; 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, 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, securities are classified as Level 3 within the valuation hierarchy. 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): December 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 432 $ 432 $ — $ — U.S. Treasury securities 414,095 414,095 — — Certificate of deposit 1,543 — 1,543 — Total $ 416,070 $ 414,527 $ 1,543 $ — December 31, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 34,821 $ 34,821 $ — $ — U.S. Treasury securities 477,125 477,125 — — Total $ 511,946 $ 511,946 $ — $ — Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Impairment of Long-Lived Assets Long-lived assets include property and equipment. We review the carrying value of long-lived assets for impairment whenever events or changes in circumstances indicate that the assets may not be recoverable. We recognize an impairment loss when the total estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount. Through December 31, 2016, there have been no such impairment losses. Revenue Recognition We recognize revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; transfer of technology has been completed or services have been rendered; our price to the customer is fixed or determinable, and collectability is reasonably assured. The terms of our collaborative research and development agreements include upfront 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 any commercialized products. Multiple-Element Revenue Arrangements. Our collaborations primarily represent multiple-element revenue arrangements. To account for these transactions, we determine the elements, or deliverables, included in the arrangement and determine which deliverables are separable for accounting purposes. We consider delivered items to be separable if the delivered items have stand-alone value to the customer. If the delivered items are separable, we allocate arrangement consideration to the various elements based on each element’s relative selling price. The identification of individual elements in a multiple-element arrangement and the estimation of the selling price of each element involve significant judgment, including consideration as to whether each delivered element has standalone value to the customer. The revenue recognition standard established the hierarchy of determining the estimated selling price for deliverables within each agreement using vendor-specific objective evidence (VSOE) of selling price, if available, or third party evidence of selling price if VSOE is not available, or our best estimate of selling price, if neither VSOE nor third party evidence is available. Determining the best estimate of selling price for a deliverable requires significant judgment. We use our best estimate of selling price to estimate the selling price for licenses to our proprietary technology since the VSOE or third party evidence of selling price for these deliverables is not available. We recognize consideration allocated to an individual element when all other revenue recognition criteria are met for that element. Our multiple-element revenue arrangements generally include the following: • Exclusive Licenses. The deliverables under our collaboration agreements generally include exclusive licenses to discover, develop, manufacture and commercialize certain compounds. To account for this element of the arrangement, we evaluate whether the exclusive license has standalone value apart from the undelivered elements to the collaboration partner based on the consideration of the relevant facts and circumstances of each arrangement, including the research and development capabilities of the collaboration partner and other market participants. We recognize arrangement consideration allocated to licenses upon delivery of the license if facts and circumstances indicate that the license has standalone value apart from the undelivered elements, which generally include research and development services. If facts and circumstances indicate that the delivered license does not have standalone value from the undelivered elements, we recognize the revenue as a combined unit of accounting. We have determined that some of our exclusive licenses lack standalone value apart from the related research and development services. In those circumstances we recognize collaboration revenue from non-refundable upfront and license fees in the same manner as the undelivered item(s), which is generally the period over which we provide the research and development services. For circumstances in which upfront and license fees are contingently refundable, we defer the recognition of the upfront and license fees until such time that the consideration is considered to be fixed or determinable. • Research and Development Services. The deliverables under our collaboration and license agreements generally include deliverables related to research and development services we perform on behalf of the collaboration partner. As the provision of research and development services is a part of our central operations and we are principally responsible for the performance of these services under the agreements, we recognize revenue on a gross basis for research and development services as we perform those services. Additionally, we recognize research funding related to collaborative research and development efforts as revenue as we perform or deliver the related services in accordance with contract terms as long as we will receive payment for such services upon standard payment terms. Milestone Revenue . Our collaboration and license agreements generally include contingent payments and milestone payments related to specified research, development and regulatory milestones and sales-based milestones. Research, development and regulatory contingent payments and milestone payments are typically receivable under our collaborations when our collaborator claims or selects a target or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, upon receipt of actual marketing approvals of a covered product or for additional indications, or upon the first commercial sale of a covered product. Sales-based milestones are typically receivable when annual sales of a covered product reach specified levels. At the inception of each arrangement that includes milestone payments, we evaluate whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. We evaluate factors such as the scientific, regulatory, commercial and other risks that we must overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement in making this assessment. We have elected to adopt the Accounting Standards Codification (ASC) 605-28, Revenue Recognition—Milestone Method Research and Development Expenses Research and development expenses consist of costs we incur for our own and for sponsored and collaborative research and development activities. Expenses we incur related to collaborative research and development agreements approximate the revenue recognized under these agreements. Research and development costs are expensed as incurred. Research and development costs consist of salaries and benefits, including associated stock-based compensation, laboratory supplies and facility costs, as well as fees paid to other entities that conduct certain research and development activities on our behalf. We estimate preclinical study and clinical trial expenses based on the services performed pursuant to contracts with research institutions, CROs, and CMOs that conduct and manage preclinical studies and clinical trials on our behalf based on actual time and expenses incurred by them. Further, we accrue expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. We monitor patient enrollment levels and related activity to the extent reasonably possible and adjust estimates accordingly. If we do not identify costs that we have begun to incur or if we underestimate or overestimate the level of services performed or the costs of these services, our actual expenses could differ from our estimates. To date, we have not experienced significant changes in our estimates of preclinical studies and clinical trial accruals. We expense payments for the acquisition and development of technology as research and development costs if, at the time of payment, the technology: is under development; is not approved by the U.S. Food and Drug Administration or other regulatory agencies for marketing; has not reached technical feasibility; or otherwise has no foreseeable alternative future use. Stock-Based Compensation We recognize compensation expense using a fair-value-based method for costs related to all share-based payments, including restricted stock and stock options. For restricted stock awards, or RSAs, stock-based compensation cost related to employees and directors is based on the closing market value of our common stock at the date of grant and is recognized as expense ratably over the requisite service period. For stock option awards, stock-based compensation cost related to employees and directors is measured at the grant date, based on the fair-value-based measurement of the award estimated using the Black-Scholes option-pricing model, and is recognized as expense over the requisite service period on a straight-line basis. We are required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. We use historical data to estimate pre-vesting option forfeitures and record stock-based compensation expense only for those awards that we expect to vest. Restricted stock awards granted to individual service providers who are not employees or directors are accounted for at fair value by remeasuring the cost based on the closing stock price at the end of that reporting period. Options granted to individual service providers who are not employees or directors are accounted for at estimated fair value using the Black-Scholes option-pricing model and are subject to periodic remeasurement over the period during which the services are rendered. Income Taxes We account for income taxes using the liability method, under which deferred tax assets and liabilities are determined based on differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Our income tax benefit for 2016 relates to our ability to carry back 2016 losses to the 2015 tax year and to obtain a refund of taxes paid related to a prior period. Valuation allowances are provided when the expected realization of the deferred tax assets does not meet the more-likely-than-not criteria. As a result, deferred tax assets at the end of 2016 are subject to a full valuation allowance. We are required to determine whether it is more likely than not that a tax position will be sustained upon examination by the appropriate taxing authorities before any part of the benefit can be recorded in the financial statements. It is our practice to recognize interest and penalties related to unrecognized tax benefits, if any, as a component of income tax expense. Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers: Topic 606 In March, April, May and December 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations , ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing , ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients to provide supplemental adoption guidance and clarification to ASU 2014-09 and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers . The effective date for these new standards is the same as the effective date and transition requirements for ASU 2014-09. We expect to adopt ASU 2014-09 in the first quarter of 2018 using the modified retrospective method. The adoption of ASU 2014-09 may have a material effect on our financial statements. To date, we have derived our revenues from license and collaboration agreements. The consideration we are eligible to receive under these agreements includes upfront payments, research and development funding, milestone payments and royalties. Each license and collaboration agreement is unique and will need to be assessed separately under the five-step process under the new standard. We have started our preliminary assessment of our active license and collaboration agreements. We expect that our evaluation of the accounting for collaboration agreements under the new revenue standard could identify material changes from the current accounting treatment. ASU 2014-09 differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments. Under our current accounting policy, we recognize milestone revenue using the milestone method specified in ASC 605-28, which generally results in the recognition of the milestone payment as revenue in the period that the milestone is achieved. However, under the new accounting standard, it is possible to start to recognize milestone revenue before the milestone is achieved, subject to management’s assessment of whether it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. In addition, the current accounting standards include a presumption that revenue from up-front non-refundable fees would be recognized ratably over the performance period, unless another attribution method was determined to more closely approximate the delivery of the goods or services to the customer. The new accounting standard does not have a presumption that entities would default to a ratable attribution approach and will require entities to determine an appropriate attribution method using either output or input methods. As such, the amount and timing of revenue recognition for our license and collaboration agreements may change under the new revenue standard. In February 2016, FASB issued ASU 2016-02, Leases. all annual and interim reporting periods thereafter. E In March 2016, FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting This standard makes several modifications to Topic 718 related to the accounting for forfeitures, employer tax withholding on share-based compensation and the financial statement presentation of excess tax benefits or deficiencies. ASU 2016-09 also clarifies the statement of cash flows presentation for certain components of share-based awards. The We expect to adopt ASU 2016-09 in the first quarter of 2017 and are evaluating the impact that the adoption of ASU 2016-09 will have on our consolidated financial statements and related disclosures.

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	12 Months Ended
	Dec. 31, 2016
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	3. Cash Equivalents and Marketable Securities The following is a summary of our cash equivalents and marketable securities at December 31, 2016 and 2015 (in thousands): December 31, 2016 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 432 $ — $ — $ 432 U.S. Treasury securities 414,134 54 (93 ) 414,095 414,566 54 (93 ) 414,527 Less: cash equivalents (432 ) — — (432 ) Total marketable securities $ 414,134 $ 54 $ (93 ) $ 414,095 December 31, 2015 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 34,821 $ — $ — $ 34,821 U.S. Treasury securities 477,239 13 (127 ) 477,125 512,060 13 (127 ) 511,946 Less: cash equivalents (144,470 ) — 19 (144,451 ) Total marketable securities $ 367,590 $ 13 $ (108 ) $ 367,495 As of December 31, 2016, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Estimated Amortized Fair Cost Value Debt securities maturing: In one year or less $ 402,644 $ 402,619 In one to two years 11,490 11,476 Total marketable securities $ 414,134 $ 414,095 Our cash equivalents and marketable securities have an average maturity of approximately 4 months and the longest maturity is 13 months. We determined that the gross unrealized losses of $93,000 on our marketable securities as of December 31, 2016 were temporary in nature and related primarily to interest rate shifts rather than significant changes in the underlying credit quality of the securities that we hold. 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 December 31, 2016. There were no sales of available-for-sale securities in any of the periods presented.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Property and Equipment	4. Property and Equipment Property and equipment consist of the following (in thousands): December 31, 2016 2015 Computer equipment and software $ 1,467 $ 1,399 Furniture and fixtures 804 804 Laboratory equipment 14,853 11,887 Leasehold improvements 2,468 2,396 19,592 16,486 Less: accumulated depreciation and amortization (13,385 ) (11,947 ) Property and equipment, net $ 6,207 $ 4,539

Other Accrued Liabilities

Other Accrued Liabilities	12 Months Ended
	Dec. 31, 2016
Payables And Accruals [Abstract]
Other Accrued Liabilities	5. Other Accrued Liabilities Other accrued liabilities consist of the following (in thousands): December 31, 2016 2015 Clinical development $ 6,831 $ 1,966 Manufacturing 4,463 333 Trade Payable 3,729 3,252 Other 412 331 Total accrued liabilities $ 15,435 $ 5,882

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stockholders' Equity	6. Stockholders’ Equity Equity Incentive Plans Our Board of Directors, or Board, and stockholders previously approved the 2002 Equity Incentive Plan, or the 2002 Plan, and the 2010 Equity Incentive Plan, or the 2010 Plan, and collectively with the 2002 Plan, the Prior Plans. The 2002 Plan terminated in March 2012. In September 2013, our stockholders approved the 2013 Omnibus Incentive Plan, or the 2013 Plan. As of September 23, 2013, the effective date of the 2013 Plan, we suspended the 2010 Plan and no additional awards may be granted under the 2010 Plan. Any shares of common stock covered by awards granted under the Prior Plans that terminate after September 23, 2013 by expiration, forfeiture, cancellation or other means without the issuance of such shares were added to the 2013 Plan reserve. The initial number of shares of common stock available for issuance under the 2013 Plan was 3,500,000, which includes the 1,069,985 shares of common stock that were available for issuance under the Prior Plans as of the effective date of the 2013 Plan. Unless our Board provides otherwise, beginning on January 1, 2014 and continuing until the expiration of the 2013 Plan, the total number of shares of common stock available for issuance under the 2013 Plan will automatically increase annually on January 1 by 4% of the total number of issued and outstanding shares of common stock as of December 31 of the immediately preceding year. As of December 31, 2016, 1,340,666 shares of common stock were available for future issuance of options, restricted stock and other stock-based awards under the 2013 Plan. Incentive stock options may be granted with an exercise price of not less than estimated fair value, and nonstatutory stock options may be granted with an exercise price of not less than 85% of the estimated fair value of the common stock on the date of grant. Stock options granted to a stockholder owning more than 10% of our voting stock must have an exercise price of not less than 110% of the estimated fair value of the common stock on the date of grant. For all stock options granted prior to our IPO, our Board determined the estimated fair value of our common stock. For all stock options granted after the completion of our IPO in September 2013, the fair value for our underlying common stock is determined using the closing market price on the date of grant. Stock options are granted with terms of up to ten years and generally vest over a period of four years. RSAs may be granted for no consideration (other than par value of the shares of stock). The fair value of RSAs is based upon the closing price of our common stock on the date of grant. RSAs generally vest over one and a half to three years and are nontransferable until the awards vest. In September 2013, our stockholders approved the 2013 Employee Stock Purchase Plan, or the ESPP, which became effective as of September 23, 2013. We initially reserved a total of 250,000 shares of common stock for issuance under the ESPP. Unless our Board provides otherwise, beginning on January 1, 2014 and continuing until the expiration of the ESPP, the total number of shares of common stock available for issuance under the ESPP will automatically increase annually on January 1 by the lesser of (i) 1% of the total number of issued and outstanding shares of common stock as of December 31 of the immediately preceding year, or (ii) 300,000 shares of common stock. As of December 31, 2016, 714,951 shares of common stock were available for issuance under the ESPP. The following table summarizes option activity under our stock plans and related information: Options Outstanding Weighted- Weighted- Average Average Exercise Remaining Aggregate Number Price Contractual Intrinsic of Shares Per Share Terms Value (in years) (in thousands) Balance at January 1, 2016 3,028,714 $ 12.62 Options granted 1,448,850 $ 44.32 Options exercised (884,139 ) $ 7.74 Options forfeited (138,958 ) $ 21.44 Options expired (128 ) $ 18.37 Balance at December 31, 2016 3,454,339 $ 26.80 Options exercisable at December 31, 2016 1,308,431 $ 13.73 6.44 $ 47,603 Options vested and expected to vest at December 31, 2016 3,399,919 $ 26.95 8.08 $ 79,094 The weighted-average grant-date fair value per share of stock options granted during the years ended December 31, 2016, 2015 and 2014 was $27.95, $14.18 and $8.39 per share, respectively. The total intrinsic value of options exercised during the years ended December 31, 2016, 2015 and 2014 was $30.8 million, $10.0 million and $4.2 million, respectively. We recorded stock-based compensation expense related to options granted to employees and directors of approximately $11.1 million, $4.5 million and $2.9 million for the years ended December 31, 2016, 2015 and 2014, respectively. Stock-based compensation expense related to options granted to individual service providers who are not employees or directors was approximately $309,000, $266,000 and $134,000 for the years ended December 31, 2016, 2015 and 2014, respectively. As of December 31, 2016, there was $39.8 million of total unrecognized compensation expense related to unvested employee and director stock options, net of forfeitures, that we expect to recognize over a weighted-average period of 2.9 years. Restricted Stock Awards RSAs are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting and are unforfeitable once fully vested. The fair value of RSAs was based upon the closing sales price of our common stock on the grant date. The following table summarizes the RSAs activity under our stock plans and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at January 1, 2016 1,574,870 $ 19.71 RSAs granted 395,430 $ 42.75 RSAs vested (800,554 ) $ 19.04 RSAs forfeited (128,817 ) $ 20.87 Unvested balance at December 31, 2016 1,040,929 $ 28.84 The total fair value on the date of vesting of RSAs vested in 2016, 2015 and 2014 was $33.2 million, $42,000, and $54,000, respectively. We recorded stock-based compensation expense related to RSAs granted to employees and directors of approximately $20.2 million, $6.2 million and $0 million for the years ended December 31, 2016, 2015 and 2014, respectively. Stock-based compensation expense related to RSAs granted to individual service providers who are not employees or directors was approximately $673,000, $85,000 and $0 for the years ended December 31, 2016, 2015 and 2014, respectively. As of December 31, 2016, there was $15.9 million of unrecognized compensation cost related to unvested RSAs, net of forfeitures, that we expect to recognize over a weighted-average period of 1.1 years. Employee Stock Purchase Plan Under our ESPP, employees can purchase shares of our common stock based on a percentage of their compensation subject to certain limits. The purchase price per share is equal to the lower of 85% of the fair market value of our common stock on the offering date or the purchase date with a six-month look-back feature. ESPP purchases are settled with common stock from the ESPP’s previously authorized and available pool of shares. We issued a total of 45,647 shares under the ESPP in 2016. The compensation expense related to the ESPP was $602,000, $455,000 and $339,000 for the years ended December 31, 2016, 2015 and 2014, respectively. As of December 31, 2016, there was $253,000 of unrecognized compensation cost related to the ESPP, which we expect to recognize over 4.5 months. Stock-Based Compensation Employee stock-based compensation expense recognized was calculated based on awards ultimately expected to vest and has been reduced for estimated forfeitures. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Total stock-based compensation expense recognized was as follows: Year Ended December 31, (in thousands) 2016 2015 2014 Research and development $ 17,960 $ 6,362 $ 1,761 General and administrative 14,925 5,105 1,657 Total $ 32,885 $ 11,467 $ 3,418 We estimated the fair value of each award using the Black-Scholes option-pricing model based on the date of grant of such award with the following assumptions: Options ESPP Year Ended December 31, Year Ended December 31, 2016 2015 2014 2016 2015 2014 Expected term (years) 5.5-6.3 5.5-6.1 5.3-6.7 0.5 0.5 0.5 Expected volatility 69.0-74.0% 71.0-76.0% 85.0% 47.0-57.0% 75.0-96.0% 49.0-83.0% Risk-free interest rate 1.3-1.8% 1.4-1.9% 1.6-2.0% 0.4-0.6% 0.1-0.3% 0.1% Expected dividend yield 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% The expected term of options granted represents the period of time that we expect options granted to remain outstanding, which we determined using the simplified method as we have insufficient historical information to provide a basis for estimate. The expected term of the ESPP rights is equal to the six-month look-back period. Volatility for options granted in 2013 is based on the average historical volatility of a peer group of public companies over the expected term. Volatility for options granted in 2014 and 2015 is based on the average of the historical volatility of our stock price and a peer group of public companies. We selected the peer group on the basis of operational and economic similarity with our principal business operations. Volatility for options granted subsequent to 2015 is based on the historical volatility of our stock price since we became publicly traded. Volatility for ESPP rights is equal to our historical volatility over the six-month look-back period. The risk-free interest rate for the expected term of the options is based on the U.S. Treasury yield curve with a maturity equal to the expected term in effect at the time of grant. We have not paid, and do not anticipate paying, cash dividends on our shares of common stock; therefore, the expected dividend yield is zero.

Earnings per Share

Earnings per Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Earnings per Share	7. Earnings per Share The computation of basic income (loss) per share is based on the weighted-average number of our common shares outstanding. The computation of diluted income (loss) per share is based on the weighted-average number of our common shares outstanding and dilutive potential common shares, which include principally shares that may be issued under our equity incentive plans, determined using the treasury stock method. The following table sets forth the computation of basic and diluted net income (loss) (in thousands, except per share data): Year Ended December 31, 2016 2015 2014 Numerator: Net income (loss) $ (65,697 ) $ 249,647 $ (37,424 ) Denominator: Denominator for basic income (loss) per share - weighted-average shares 26,955 25,661 20,865 Effect of dilutive securities: Equity incentive plans — 1,374 — Denominator for diluted income (loss) per share 26,955 27,035 20,865 Income (loss) per share - Basic $ (2.44 ) $ 9.73 $ (1.79 ) Income (loss) per share - Diluted $ (2.44 ) $ 9.23 $ (1.79 ) We did not include potentially dilutive securities that would have an antidilutive effect. In 2016 and 2014, this consisted of all stock options to purchase common stock and RSAs. In 2015, this consisted of certain stock options to purchase common stock and RSAs. We excluded the following securities from the calculation of diluted net income (loss) per share as the effect would have been antidilutive (in thousands): Year Ended December 31, 2016 2015 2014 Options to purchase common stock 2,981 187 2,379 RSAs 1,278 8 9 4,259 195 2,388

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2016
Postemployment Benefits [Abstract]
Employee Benefit Plans	8. Employee Benefit Plans We sponsor a 401(k) plan that stipulates that eligible employees can elect to contribute to the 401(k) plan, subject to certain limitations, up to the lesser of the statutory maximum or 100% of eligible compensation on a pre-tax basis. We pay the administrative costs for the plan. Effective January 1, 2015, we elected to match employee contributions to the 401(k) plan, or the company match, as permitted by the 401(k) plan. During 2016, we made matching contribution in an amount equal to 50% of the amount contributed by the employee up to an annual maximum company match per employee equal to $6,000. We recorded company match expense of $712,000 for the year ended December 31, 2016. During 2015, we made matching contributions in an amount equal to 50% of the amount contributed by the employee up to an annual maximum company match per employee equal to the lesser of (i) 4% of such employee’s compensation, or (ii) $6,000. During 2015, we delivered the company match through the issuance of shares of our common stock. We delivered 17,803 shares of our common stock as the company match in 2015 and recorded 401(k) plan company match expense of $477,000 for the year ended December 31, 2015.

Collaborative Research and Deve

Collaborative Research and Development Agreements	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborative Research and Development Agreements	9. Collaborative Research and Development Agreements Bristol-Myers Squibb Company License and Collaboration Agreement On October 14, 2015, we entered into a license and collaboration agreement, or the cabiralizumab collaboration agreement, with Bristol-Myers Squibb Company, or BMS, pursuant to which we granted BMS exclusive global rights to develop and commercialize certain colony stimulating factor-1 receptor, or CSF1R, antibodies, including our monoclonal CSF1R inhibiting antibody that we refer to as cabiralizumab, and all modifications, derivatives, fragments, or variants of such antibodies, each of which we refer to as a licensed antibody. Under the terms of the cabiralizumab collaboration agreement, BMS is responsible, at its expense, for developing products containing licensed antibodies, each of which we refer to as a licensed product, under a development plan, subject to our option, at our own expense, to conduct certain studies, including registration-enabling studies to support approval of cabiralizumab in PVNS and in combination with our proprietary internal or in-licensed compounds, including in oncology. BMS is responsible for manufacturing and commercializing each licensed product and we will retain rights to a U.S. co-promotion option. This supersedes the clinical trial collaboration agreement we entered into with BMS in November 2014. We continue to conduct the current Phase 1a/1b clinical trial to evaluate the safety, tolerability and preliminary efficacy of combining Opdivo ® Pursuant to the cabiralizumab collaboration agreement, BMS made an upfront payment of $350.0 million to us in December 2015. We applied ASC 605-25, Multiple-Deliverable Revenue Arrangements Additionally, we are eligible to receive up to $1.05 billion in development and regulatory milestone payments per anti-CSF1R product for oncology indications and up to $340 million in development and regulatory milestone payments per anti-CSF1R product for non-oncology indications, as well as royalties ranging from the high teens to the low twenties, such royalties to be enhanced in the U.S. in the event that we exercise our co-promotion option. We determined that these contingent payments will not be accounted for under the milestone method of revenue recognition as the events that trigger these payments under the agreement with BMS do not meet the definition of a milestone under ASC 605-28, Milestone Method of Revenue Recognition Under the original clinical trial collaboration agreement, BMS paid us an upfront fee of $30.0 million in December 2014. Initially, the $30.0 million upfront fee was contingently refundable if certain change of control events occurred prior to a specified date. As such, the upfront fee was not considered to be fixed or determinable at that time and was recorded as deferred revenue as of December 31, 2014. Under the cabiralizumab collaboration agreement, the $30.0 million upfront fee under the original clinical trial collaboration is no longer contingently refundable. Therefore, upon the effectiveness of the cabiralizumab collaboration agreement, the upfront fee became fixed or determinable and we started recognizing revenue ratably, using a cumulative catch up method, over the estimated performance period ending in 2019. We will periodically evaluate the estimated performance period based on the progress made under the collaboration. During 2016 and 2015, we recognized $5.9 million and $6.4 million, respectively, of revenue relating to the upfront fee. For the years ended December 31, 2016 and 2015, we recognized $14.4 million and $359.9 million, respectively, of revenue under the cabiralizumab collaboration agreement. As of December 31, 2016 and 2015, we had deferred revenue relating to the collaboration of $17.7 million and $23.6 million, respectively. Immuno-Oncology Research Collaboration In March 2014, we entered into a research collaboration and license agreement, or the immuno-oncology research collaboration, with BMS, to carry out a research program to (i) discover novel interacting proteins in two undisclosed immune checkpoint pathways, which we refer to as the checkpoint pathways, using our target discovery platform; (ii) further the understanding of target biology with respect to targets in these checkpoint pathways; and (iii) discover and pre-clinically develop compounds suitable for development for human therapeutic uses against targets in these checkpoint pathways. Under the immuno-oncology collaboration, we granted BMS an exclusive, worldwide license to research, develop and commercialize products directed towards certain targets in the checkpoint pathways. BMS will have an option to take exclusive licenses to additional targets we may identify in these checkpoint pathways during the course of the immuno-oncology research collaboration. Based on data arising from our initial screens, in January 2016, we amended the immuno-oncology research collaboration to add an additional checkpoint pathway to the research program, for a total of three undisclosed immune checkpoint pathways. We received an upfront payment of $20.0 million from BMS in April 2014 in connection with our entry into the immuno-oncology research collaboration and expect to receive $9.5 million in research funding over the course of the three-year research term based on the research activities currently planned under the research plan. BMS may extend the research term for two additional one-year periods on a year-by-year basis, during which extensions we would be obligated to perform additional services as agreed to with BMS and BMS would be obligated to pay us research funding with respect to such services. The initial research term under the immuno-oncology research collaboration expire in March 2017. In December 2016, BMS exercised its option to extend the research term for an additional year to March 2018. BMS has the option to extend the research term for one additional year. We applied ASC 605-25, Multiple-Deliverable Revenue Arrangements We are eligible to receive certain contingent payments with respect to each target subject to the immuno-oncology research collaboration and royalties on sales of products related to such targets, if any. In accordance with ASC 605-28, we determined that the remaining contingent payments under the immuno-oncology research collaboration do not constitute milestone payments and will not be accounted for under the milestone method of revenue recognition. The events leading to these payments under the collaboration do not meet the definition of a milestone under ASC 605-28 because the achievement of these events solely depends on BMS’s performance. Any revenue from these contingent payments would be subject to an allocation of arrangement consideration and would be recognized over any remaining period of performance obligations, if any, relating to the collaboration. If we have no remaining performance obligations under the immuno-oncology research collaboration at the time the contingent payment is triggered, we would recognize the contingent payment as revenue in full upon the triggering event. In connection with the immuno-oncology research collaboration, BMS purchased 994,352 shares of our common stock at a price per share of $21.16, for an aggregate purchase price of $21.0 million. We determined that the purchase price of $21.16 per share exceeded the fair value of our common stock by $2.4 million and, therefore, recorded the $2.4 million as deferred revenue to be recognized in the same manner as the $20.0 million upfront payment. For the years ended December 31, 2016, 2015, and 2014, we recognized $7.7 million, $7.0 million and $6.0 million, respectively, of revenue under the immuno-oncology research collaboration. As of December 31, 2016 and 2015, we had deferred revenue relating to the immuno-oncology research collaboration of $10.6 million and $16.8 million, respectively. The immuno-oncology research collaboration will terminate upon the expiration of all payment obligations under the collaboration. In addition, BMS may terminate the immuno-oncology research collaboration in its entirety or on a collaboration target-by-collaboration target basis at any time with advance written notice and either party may terminate the collaboration in its entirety or on a collaboration target-by-collaboration target basis with written notice for the other party’s material breach if such other party fails to timely cure the breach or immediately upon certain insolvency events. GlaxoSmithKline LLC Respiratory Diseases Collaboration In April 2012, we entered into 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, function with a particular focus on identifying novel protein therapeutics and antibody targets. We conducted six customized cell-based screens of our protein library under this agreement. Under the terms of the agreement, GSK paid us an upfront technology access payment of $7.5 million at the inception of the respiratory diseases collaboration We applied ASC 605-25, Multiple-Deliverable Revenue Arrangements Pursuant to the respiratory diseases collaboration, GSK exercised its option to expand the research plan to include two additional screening assays. We received $2.0 million in additional research funding for the two additional screening assays as of December 31, 2015. 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 by $0.7 million that GSK is obligated to pay us under our collaboration. Such funding was fully received as of December 31, 2016. We are eligible to receive certain option and selection payments, payments for the achievement of certain development activities, and royalties on the sales of products related to targets GSK selects for exclusive development, if any. We are eligible to receive up to $124.3 million in potential target evaluation and selection fees and contingent payments with respect to each protein target for which GSK will have sole responsibility for the further development and commercialization of products that incorporate or target such protein target, or a track 1 target. GSK is also obligated to pay us tiered low- to mid-single digit royalties on global net sales for each product that incorporates or targets each such track 1 target. We are eligible to receive up to $193.8 million in potential target evaluation and selection fees and contingent payments with respect to each protein target for which we will develop biologics that incorporate or target the protein targets through to clinical proof of mechanism in either a phase 1 clinical trial or a phase 2 clinical trial, or a track 2 target. GSK is also obligated to pay us tiered high-single to low-double digit royalties on global net sales for each product that incorporates or targets each such track 2 target. In accordance with ASC 605-28, we determined that the remaining contingent payments under the respiratory diseases collaboration do not constitute milestone payments and we will not account for such payments under the milestone method of revenue recognition. In connection with our entry into the respiratory diseases collaboration, GSK purchased 381,693 shares of our Series A-3 convertible preferred stock at a price of $26.20 per share, resulting in net cash proceeds to us of $10.0 million. We determined that the purchase price of $26.20 per share exceeded the estimated fair value of the Series A-3 convertible preferred stock by $3.1 million and, therefore, recorded the $3.1 million as deferred revenue to be recognized in the same manner as the upfront technology access payment. In the years ended December 31, 2016, 2015 and 2014, we received $3.6 million, $3.9 million and $3.9 million, respectively, of research funding and milestones related to all research being performed under the respiratory diseases collaboration. Total revenue recognized under the respiratory diseases collaboration was $5.0 million, $7.3 million and $6.4 million for the years ended December 31, 2016, 2015 and 2014, respectively. As of December 31, 2016, we fully recognized the deferred revenue related to the respiratory diseases collaboration as we completed our obligation to provide research service. As of December 31, 2015, we had deferred revenue related to this agreement of $1.7 million. Additionally, GSK is obligated to reimburse us for certain specialized research and development costs associated with the screens under the respiratory diseases collaboration. The respiratory diseases collaboration will terminate upon the expiration of the royalty terms of any products that incorporate or target a protein exclusively licensed under the collaboration. In addition, GSK may terminate this agreement at any time with advance written notice, and either party may terminate this agreement with written notice for the other party’s material breach if such party fails to cure the breach or immediately in the case of failure to comply with certain anti-bribery and anti-corruption policies or upon certain insolvency events. FP-1039 License and Collaboration In March 2011, we entered into a license and collaboration agreement, or the FP-1039 license, with Human Genome Sciences, Inc., or HGS, which was acquired by GSK in 2012. Pursuant to the FP-1039 license, we granted GSK an exclusive license to develop and commercialize our FP-1039 product and other FGFR1 fusion proteins in the United States, the European Union and Canada. We received an upfront license fee of $50.0 million from GSK in March 2011 in connection with our entry into the FP-1039 license. We identified the initial license, associated technology transfer and services for the conduct of the then-concluding FP-1039 Phase 1 clinical trial as substantive deliverables under the FP-1039 license. As of December 31, 2011, all deliverables under the FP-1039 license were fully delivered and we recognized the related $50.0 million of upfront license fee fully as revenue. In addition, GSK was obligated to pay us for the costs of all FP-1039 related research and development activities we elected to undertake on behalf of GSK. For the years ended December 31, 2016, 2015 and 2014, we recognized $21,000, $0.1 million and $0.1 million, respectively, in revenue from GSK related to development costs associated with FP-1039. In March 2016, GSK delivered to us a written notice of termination of the FP-1039 license. Pursuant to the terms of the FP-1039 license, termination of the FP-1039 license became effective on September 5, 2016, 180 days after GSK’s notice of termination. Pursuant to the terms of the FP-1039 license, we elected to have GSK complete the conduct of the Phase 1b clinical trial of FP-1039 that GSK is currently conducting, at GSK’s expense. Muscle Diseases Collaboration 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. Under the terms of the muscle diseases collaboration, we received an upfront technology access payment of $7.0 million in August 2010. The $7.0 million upfront technology access payment was recorded as deferred revenue, which we initially began recognizing over the initial three-year research period under the agreement. We fully recognized the deferred revenue related to this agreement in 2014 as we completed our obligation to provide research services. In May 2011, we amended the agreement to expand the research plan in scope and duration to include an additional cell-based screen and an in vivo We were eligible to receive certain option and selection payments related to targets identified in the collaboration. We are also eligible to receive payments for the achievement of certain development activities and royalties on the sales of products related to targets GSK selected for exclusive development. We were eligible to receive up to $1.8 million of option and selection payments per target when GSK claimed and selected a target for further development. In accordance with ASC 605-28, we concluded that these payments under the agreement with GSK were substantive and accounted for these milestones under the milestone method of revenue recognition. In accordance with ASC 605-28, we determined that the remaining contingent payments under the agreement with GSK do not constitute milestone payments and will not be accounted for under the milestone method of revenue recognition. The events leading to these payments under the muscle diseases collaboration do not meet the definition of a milestone under this standard because the achievement of these events is solely dependent on GSK’s performance. In connection with our entry into the muscle diseases collaboration, GSK purchased 329,597 shares of our Series A-2 convertible preferred stock at a price of $22.76 per share, resulting in net cash proceeds to us of $7.5 million. We determined that the purchase price of $22.76 per share exceeded the estimated fair value of the Series A-2 convertible preferred stock by $3.0 million and, therefore, recorded the $3.0 million as revenue in the same manner as the upfront technology access payment. In December 2012, GSK selected a protein therapeutic target for further evaluation. We received the related selection fee of $0.3 million in 2013. In September 2013, we entered into an agreement with GSK to extend the evaluation period for this protein therapeutic target by approximately eight months. In connection with the extension of the evaluation period, GSK paid a $0.2 million extension fee, which we have fully recognized in revenue over the eight-month extension period in 2014. In October 2013, GSK exercised its right to reserve for further evaluation several protein therapeutic targets for muscle diseases that we discovered pursuant to the muscle diseases collaboration. In connection with reserving these targets for further evaluation, GSK paid us a selection fee of $0.3 million in 2013. In September, 2014, GSK exercised its option to license an undisclosed muscle disease target that we identified. We granted GSK an exclusive, worldwide license to products containing or directed to the target. We received a payment of $1.5 million in connection with the option exercise Total revenue recognized under the muscle diseases collaboration was $3.4 million for the year ended December 31, 2014. As of December 31, 2014, the deferred revenue related to this agreement had been fully recognized as we completed our obligation to provide research services. The muscle diseases collaboration will terminate upon the expiration of the royalty terms of any products that incorporate or target a protein exclusively licensed under the collaboration. In addition, GSK may terminate this agreement at any time with advance written notice, and either party may terminate this agreement with written notice for the other party’s material breach if such party fails to cure the breach or upon certain insolvency events. 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 applied ASC 605-25, Multiple-Deliverable Revenue Arrangements, to evaluate the appropriate accounting for this agreement. In accordance with this guidance, we concluded that we should account for the arrangement as a single unit of accounting and recognize the agreement consideration in the same manner as the final deliverable of the research services. Under the terms of the fibrosis and CNS collaboration, UCB paid us an upfront payment of $6.0 million in March 2013. In addition, UCB agreed to pay us $6.6 million for a technology fee and $2.0 million for research funding. All of which was recorded as deferred revenue and being amortized over the initial five-year research period under the agreement. As of December 31, 2015, we fully collected on the technology fees and research funding under the fibrosis and CNS collaboration. We are eligible to receive certain evaluation and selection fees and contingent payments with respect to each protein target that UCB elects to obtain an exclusive license, and royalties on the sales of products related to such targets, if any. We are eligible to receive up to $0.4 million of target evaluation and selection fees with respect to each target we have offered to UCB in the collaboration. In accordance with ASC 605-28, we concluded that these fees under the agreement with UCB are substantive and should be accounted for under the milestone method of revenue recognition. During 2016 and 2015, we received $0.4 and $0.1 million in target evaluation and selection fees, respectively. In accordance with ASC 605-28, we determined that the remaining contingent payments under the agreement do not constitute milestone payments and will not be accounted for under the milestone method of revenue recognition. The events leading to these payments under the agreement with UCB do not meet the definition of a milestone under ASC 605-28 because the achievement of these events solely depends on UCB’s performance. For the years ended December 31, 2016, 2015 and 2014, we recognized $3.5 million, $4.0 million and $3.2 million of revenue, respectively, under the fibrosis and CNS collaboration. As of December 31, 2016 and 2015, we have deferred revenue relating to this agreement of $3.7 million and $6.7 million, respectively. Additionally, UCB is obligated to reimburse us for certain specialized research and development costs associated with the screens under the agreement. Our initial research activities under this agreement were completed in March 2016. Upon the completion of those research activities, UCB has up to a two-year evaluation period during which we may be obligated to perform additional services at the request of UCB. The agreement will terminate upon the expiration of the royalty terms of any products that incorporate or target a protein exclusively licensed under the collaboration. In addition, UCB may terminate this agreement at any time with advance written notice, and either party may terminate the agreement with written notice for the other party’s material breach if such other party fails to timely cure the breach or upon certain insolvency events. bluebird bio, Inc. License Agreement In May 2015, we entered into an exclusive license agreement, or the bluebird license agreement, with bluebird bio, Inc., or bluebird, under which we licensed to bluebird human antibodies to an undisclosed cancer target to research, develop and commercialize chimeric antigen receptor (CAR) T cell therapies using these antibodies. Under the bluebird license agreement, bluebird paid us a $1.5 million upfront fee in 2015. There are no other deliverables under the agreement other than the license grant. We recognized the $1.5 million upfront fee as revenue upon delivery of the license grant, which was completed in 2015. In January 2017, bluebird delivered to us written notice of termination of the license agreement. Pursuant to the terms of the license agreement, termination will become effective on May 17, 2017, which is 120 days after bluebird’s notice of termination. Following termination, bluebird will have no future payment obligations to us in connection with the license agreement.

Acquired Technologies

Acquired Technologies	12 Months Ended
	Dec. 31, 2016
Research And Development [Abstract]
Acquired Technologies	10. Acquired Technologies Galaxy Biotech, LLC In December 2011, we entered into an exclusive license agreement with Galaxy Biotech, LLC, or Galaxy, for the development, manufacturing, and commercialization of certain anti-FGFR2b monoclonal antibodies. Under the terms of the agreement, we agreed to pay Galaxy an upfront license payment of $3.0 million. We paid the upfront payment in two equal installments in January 2012 and July 2012. As we had full access to the technology and materials upon execution of the agreement, the lead compound was in an early stage of development, and the underlying technology has no alternative future uses, we recorded the entire upfront payment to research and development expenses in our statement of operations for the year ended December 31, 2011. We are also required to make additional payments based upon the achievement of certain intellectual property, development, regulatory, and commercial milestones, as well as royalties on future net sales of products resulting from development of this purchased technology, if any. In May 2016, we amended the license agreement to revise certain milestone definitions, reduce certain milestone payments and add certain development-related milestone payments that were triggered by dosing of certain patients in the current Phase 1 clinical trial of FPA144. INBRX 110 LP In July 2015, we entered into a research collaboration and license agreement with INBRX 110 LP, or Inhibrx, to obtain (a) an exclusive, worldwide license to antibodies to GITR for therapeutic and diagnostic uses, which we refer to respectively as licensed therapeutic products and licensed diagnostic products, and (b) an exclusive option, or the option, to obtain exclusive, worldwide licenses to multi-specific antibodies developed by Inhibrx that bind to both GITR and other targets, each of which we refer to as a multi-specific product. We can exercise an option with respect to a multi-specific product within a limited period of time after (i) certain activities related to initiating clinical manufacturing of such multi-specific product or (ii) if not earlier exercised, the dosing of the first patient in a Phase 2 clinical trial of such multi-specific product. Pursuant to the agreement, we paid Inhibrx an upfront fee of $10.0 million for the license and for services to be provided by Inhibrx related to a research cell bank in July 2015. Additionally, with respect to each licensed therapeutic product, we will be obligated to pay up to $62.5 million in specified development milestone payments and (i) if such licensed therapeutic product does not receive a Breakthrough Therapy Designation from the FDA up to $280.0 million in specified regulatory and commercial milestone payments, or (ii) if such licensed therapeutic product receives a Breakthrough Therapy Designation from the FDA, up to $380.0 million in specified regulatory and commercial milestone payments. Inhibrx is also eligible for low double-digit tiered royalties on future product sales. We may pay all or a portion of milestone payments for development and regulatory events in shares of our common stock, subject to certain limitations and conditions. We would be obligated to register for resale under the Securities Act any such shares of our common stock. We expense payments for the acquisition and development of technology as research and development cost if, at the time of payment, the technology is under development, is not approved by the FDA or other regulatory agencies for marketing, has not reached technical feasibility, or otherwise has no foreseeable alternative future use. In accordance with this policy, we expensed the $8.0 million that we determined to be related to the license upon our entry into the agreement in July 2015 as research and development expense. In accordance with the ASC 730, Research and Development Costs

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes For the year ended December 31, 2016, we recorded an income tax benefit of $31.0 million as compared to an income tax expense of $37.8 million for the year ended December 31, 2015. We recorded no income tax expense for the year ended December 31, 2014 due to the loss incurred in that year. For the year ended December 31, 2015, the income tax expense was based on the taxable income generated in 2015 after utilization of our available federal and state net operating loss carryovers as well as any research credits including consideration of any applicable limitations on the use of these attributes as provided by the Internal Revenue Code and similar state statutes. For the year ended December 31, 2016, the federal tax benefit represents the reversal of the federal tax provided in 2015 due to our ability to carryback federal tax attributes generated this year but not in an amount that is lower than any minimum taxes as provided under federal law. The state tax benefit in the current year represents the reversal of prior state income tax also to an amount that is not lower than any minimum tax as provided under state law. The components of our income tax (benefit) expense were as follows: Year Ended December 31, 2016 2015 2014 Current tax (benefit) expense Federal $ (40,740 ) $ 47,369 $ — State (5,340 ) 5,473 — Total current (benefit) expense (46,080 ) 52,842 — Deferred tax (benefit) expense Federal 15,032 (15,032 ) — State — — — Total deferred tax (benefit) expense 15,032 (15,032 ) — Total tax (benefit) expense $ (31,048 ) $ 37,810 $ — The income tax (benefit) expense differs from the amount computed by applying the statutory federal income tax rate as follows (in thousands) Year Ended December 31, 2016 2015 2014 Federal statutory income tax $ (33,862 ) $ 100,610 $ (13,098 ) State statutory income tax (3,471 ) 3,558 — Nondeductible stock compensation 715 437 (501 ) Nontaxable equity premiums (248 ) (443 ) (504 ) Deferred tax assets (utilized) not benefitted 12,152 (62,705 ) 14,075 Research and orphan drug credits (8,029 ) (3,846 ) — Other permanent items 1,695 199 28 Income tax (benefit) expense $ (31,048 ) $ 37,810 $ — The tax effects of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets consist of the following (in thousands): As of December 31, 2016 2015 Net operating loss carryforwards $ 5,615 $ 941 Research and orphan drug credits 18,182 819 Deferred revenue 10,939 16,697 Stock based compensation 6,908 4,542 Capitalized license and depreciation basis differences 3,574 3,685 Reserves and accruals 1,736 3,960 Total deferred tax assets 46,954 30,644 Less: valuation allowance (46,954 ) (15,573 ) Net deferred tax assets $ — $ 15,071 Based on all available objective evidence, we determined it is more likely than not that all net deferred tax assets will not be fully realizable. The available objective evidence considered was our inability to further recover any taxes previously paid and expectation of future taxable income. Accordingly, we recorded a valuation allowance against all of its net deferred tax assets for the years ended December 31, 2016. We will continue to maintain a full valuation allowance on its net deferred tax assets until there is sufficient positive evidence to support the reversal of all or some portion of this allowance. Our valuation allowance increased by $31.4 million during 2016 and decreased by $74.1 million during 2015. At December 31, 2016, we had approximately $145.1 million of state net operating losses available for future use that expire beginning in 2017 and state research credits of approximately $12.3 million that have no expiration date. We also have federal research and Orphan Drug credits of approximately $17.2 million available for future use that expire beginning in the year 2023. We had $9.4 million, $3.4 million and $2.2 million of unrecognized tax benefits as of December 31, 2016, 2015 and 2014, respectively. The unrecognized tax benefits are primarily tax credits for all years and state net operating loss carryover related for certain prior years. We currently have a full valuation allowance against our deferred tax assets, which would impact the timing of the effective tax rate benefit, should any of these uncertain positions be favorably settled in the future. Unrecognized tax benefits may change during the next twelve months for items that arise in the ordinary course of business. As of December 31, 2016, no significant increases or decreases are expected to our uncertain tax positions within the next 12 months. As of December 31, 2016 and 2015, we had no accrued interest or penalties related to income taxes, and no such interest and penalties have been incurred through December 31, 2016. A reconciliation of our unrecognized tax benefits for the years ended December 31, 2016, 2015 and 2014 Unrecognized Income Tax Benefits Balance as of December 31, 2013 $ 1,781 Additions for prior year tax positions 11 Additions for current year tax positions 445 Balance as of December 31, 2014 2,237 Additions for prior year tax positions 615 Additions for current year tax positions 580 Balance as of December 31, 2015 3,432 Additions for prior year tax positions 4,394 Additions for current year tax positions 1,577 Balance as of December 31, 2016 $ 9,403 We file U.S. and state income tax returns with varying statutes of limitations. The tax years from inception in 2001 forward remain open to examination due to the carryover of unused net operating losses and tax credits. We have no ongoing tax examinations by tax authorities at this time.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies Operating Leases We lease our corporate office and laboratory facility under an operating lease. We entered into the initial lease in March 2010 and entered into an amendment in November 2014 to amend certain terms of the lease and to increase the amount of leased space, which we refer to collectively as the lease. The lease will expire on December 31, 2017. The lease contains scheduled rent increases over the lease term. We recognize the related rent expense for the lease on a straight-line basis over the term of the lease with the difference between the rent paid and the straight-line rent expense recorded as deferred rent. As of December 31, 2016 and 2015, deferred rent totaled $0.9 million and $1.6 million, respectively. We received lease incentives totaled $1.9 million from our landlord for a portion of the costs of leasehold improvements we made to the premises. We amortize the incentives on a straight-line basis over the term of the lease as a reduction of rent expense. As of December 31, 2016 and 2015, the unamortized leasehold improvement incentive totaled $0.3 million and $0.6 million, respectively. We entered into a new corporate office and laboratory facility lease agreement in December 2016, which we refer to as the new lease. The new lease has an initial term of 10 years, beginning on the rent commencement date, with an option to extend the lease for an additional period of five years. We do not have to pay rent until the rent commencement date. The rent commencement date is the later to occur of (i) January 1, 2018 and (ii) 30 days after the facility is ready for occupancy. Rent is reduced by 50% for the first six months. Pursuant to the terms of the new lease, we are entitled to a tenant improvement allowance of up to $14.4 million. In addition, the new lease required us to deliver an irrevocable standby letter of credit in an amount of $1.5 million to landlord for the period commencing on the effective date of the agreement until at least 60 days after the expiration of the new lease, subject to 50% reduction on the first day of the sixth lease year if certain conditions are met. Rent expense for the years ended December 31, 2016, 2015 and 2014 was $2.3 million, $2.3 million, and $1.9 million, respectively. Year ending December 31: 2017 3,461 2018 5,092 2019 7,025 2020 7,274 2021 7,524 Thereafter 51,017 Total estimated minimum payments $ 81,393 Indemnifications As permitted under Delaware law and in accordance with our bylaws, we have agreed to indemnify our officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at our request in such capacity. The term of the indemnification period is equal to the officer’s or director’s lifetime. The maximum amount of potential future indemnification is unlimited; however, we currently hold director and officer liability insurance. This insurance limits our exposure and may enable us to recover a portion of any future amounts paid. We believe that the fair value of these indemnification obligations is minimal. Accordingly, we have not recognized any liabilities relating to these obligations for any period presented. We have certain agreements with service providers and other parties with which we do business that contain indemnification provisions pursuant to which we have agreed to indemnify the party against certain types of third-party claims. We accrue for known indemnification issues when a loss is probable and can be reasonably estimated. We would also accrue for estimated incurred but unidentified indemnification issues based on historical activity. As we have not incurred any indemnification losses to date, there were no accruals for or expenses related to indemnification issues for any period presented.

Selected Quarterly Financial In

Selected Quarterly Financial Information	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information	13. Selected Quarterly Financial Information (Unaudited) The following amounts are in thousands, except per share amounts: Quarter Ended March 31, June 30, September 30, December 31, Quarterly Results of Operations 2016 2016 2016 2016 (Unaudited) Revenue $ 6,520 $ 9,229 $ 6,680 $ 8,262 Net loss (13,040 ) (13,137 ) (19,414 ) (20,106 ) Basic and diluted net loss per share (0.49 ) (0.49 ) (0.72 ) (0.73 ) Quarter Ended March 31, June 30, September 30, December 31, Quarterly Results of Operations 2015 2015 2015 2015 (Unaudited) Revenue $ 4,287 $ 6,315 $ 5,858 $ 363,341 (1) Net income (loss) (11,036 ) (11,474 ) (23,971 ) 296,128 Basic net income (loss) per share (0.44 ) (0.45 ) (0.93 ) 11.37 Diluted net income (loss) per share (0.44 ) (0.45 ) (0.93 ) 10.63 (1) Includes the $350.0 million upfront license fee from the cabiralizumab collaboration agreement. See Note 9 for further discussion. Basic and diluted net income (loss) per share is computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share amounts may not equal annual basic and diluted net income (loss) per share amounts.

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America 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.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Cash equivalents are stated at fair value.
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 entered in December 2016. We are required to maintain this restricted cash balance for the duration of the lease, which amount is subject to reduction starting in the sixth year of the lease if certain conditions are met. See Note 13 for further discussion on our lease.
Marketable Securities	Marketable Securities All marketable securities have been classified as “available-for-sale” and are carried at fair value, based upon quoted market prices. We consider our available-for-sale portfolio as available for use in current operations. Accordingly, we classify certain investments as short-term marketable securities, even though the stated maturity date may be one year or more beyond the current balance sheet date. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive income or loss and reported as a separate component of stockholders’ equity or deficit until realized. Realized gains and losses and declines in value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense), net. The cost of securities sold is based on the specific-identification method. We adjust the amortized cost of securities for amortization of premiums and accretion of discounts to maturity. We include interest on short-term investments in interest income. In accordance with our investment policy, management invests to diversify credit risk and only invests in debt securities with high credit quality, including U.S. government securities, and does not invest in mortgage-backed securities or mortgage loans. We periodically evaluate whether declines in the fair value of our investments below their cost are other than temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether we have the intent to sell the securities, and whether it is more likely than not that we will be required to sell the securities before the recovery of their amortized cost basis. If we determine that the decline in fair value of an investment is below its accounting basis and this decline is other than temporary, we would reduce the carrying value of the security we hold and record a loss for the amount of such decline. We have not recorded any realized losses or declines in value judged to be other than temporary on our investments in debt securities.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash and cash equivalents and marketable securities. Cash and cash equivalents and marketable securities are invested through banks and other financial institutions in the United States. Such deposits in the United States may be in excess of insured limits.
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. For our marketable securities, we review trading activity and pricing as of the measurement date. When sufficient quoted pricing for identical securities is not available, we use market pricing and other observable market inputs for similar securities obtained from various third-party data providers. These inputs either represent quoted prices for similar assets in active markets or have been derived from observable market data; 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, 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, securities are classified as Level 3 within the valuation hierarchy. 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): December 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 432 $ 432 $ — $ — U.S. Treasury securities 414,095 414,095 — — Certificate of deposit 1,543 — 1,543 — Total $ 416,070 $ 414,527 $ 1,543 $ — December 31, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 34,821 $ 34,821 $ — $ — U.S. Treasury securities 477,125 477,125 — — Total $ 511,946 $ 511,946 $ — $ —
Property and Equipment	Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets include property and equipment. We review the carrying value of long-lived assets for impairment whenever events or changes in circumstances indicate that the assets may not be recoverable. We recognize an impairment loss when the total estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount. Through December 31, 2016, there have been no such impairment losses.
Revenue Recognition	Revenue Recognition We recognize revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; transfer of technology has been completed or services have been rendered; our price to the customer is fixed or determinable, and collectability is reasonably assured. The terms of our collaborative research and development agreements include upfront 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 any commercialized products. Multiple-Element Revenue Arrangements. Our collaborations primarily represent multiple-element revenue arrangements. To account for these transactions, we determine the elements, or deliverables, included in the arrangement and determine which deliverables are separable for accounting purposes. We consider delivered items to be separable if the delivered items have stand-alone value to the customer. If the delivered items are separable, we allocate arrangement consideration to the various elements based on each element’s relative selling price. The identification of individual elements in a multiple-element arrangement and the estimation of the selling price of each element involve significant judgment, including consideration as to whether each delivered element has standalone value to the customer. The revenue recognition standard established the hierarchy of determining the estimated selling price for deliverables within each agreement using vendor-specific objective evidence (VSOE) of selling price, if available, or third party evidence of selling price if VSOE is not available, or our best estimate of selling price, if neither VSOE nor third party evidence is available. Determining the best estimate of selling price for a deliverable requires significant judgment. We use our best estimate of selling price to estimate the selling price for licenses to our proprietary technology since the VSOE or third party evidence of selling price for these deliverables is not available. We recognize consideration allocated to an individual element when all other revenue recognition criteria are met for that element. Our multiple-element revenue arrangements generally include the following: • Exclusive Licenses. The deliverables under our collaboration agreements generally include exclusive licenses to discover, develop, manufacture and commercialize certain compounds. To account for this element of the arrangement, we evaluate whether the exclusive license has standalone value apart from the undelivered elements to the collaboration partner based on the consideration of the relevant facts and circumstances of each arrangement, including the research and development capabilities of the collaboration partner and other market participants. We recognize arrangement consideration allocated to licenses upon delivery of the license if facts and circumstances indicate that the license has standalone value apart from the undelivered elements, which generally include research and development services. If facts and circumstances indicate that the delivered license does not have standalone value from the undelivered elements, we recognize the revenue as a combined unit of accounting. We have determined that some of our exclusive licenses lack standalone value apart from the related research and development services. In those circumstances we recognize collaboration revenue from non-refundable upfront and license fees in the same manner as the undelivered item(s), which is generally the period over which we provide the research and development services. For circumstances in which upfront and license fees are contingently refundable, we defer the recognition of the upfront and license fees until such time that the consideration is considered to be fixed or determinable. • Research and Development Services. The deliverables under our collaboration and license agreements generally include deliverables related to research and development services we perform on behalf of the collaboration partner. As the provision of research and development services is a part of our central operations and we are principally responsible for the performance of these services under the agreements, we recognize revenue on a gross basis for research and development services as we perform those services. Additionally, we recognize research funding related to collaborative research and development efforts as revenue as we perform or deliver the related services in accordance with contract terms as long as we will receive payment for such services upon standard payment terms. Milestone Revenue . Our collaboration and license agreements generally include contingent payments and milestone payments related to specified research, development and regulatory milestones and sales-based milestones. Research, development and regulatory contingent payments and milestone payments are typically receivable under our collaborations when our collaborator claims or selects a target or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, upon receipt of actual marketing approvals of a covered product or for additional indications, or upon the first commercial sale of a covered product. Sales-based milestones are typically receivable when annual sales of a covered product reach specified levels. At the inception of each arrangement that includes milestone payments, we evaluate whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. We evaluate factors such as the scientific, regulatory, commercial and other risks that we must overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement in making this assessment. We have elected to adopt the Accounting Standards Codification (ASC) 605-28, Revenue Recognition—Milestone Method
Research and Development Expenses	Research and Development Expenses Research and development expenses consist of costs we incur for our own and for sponsored and collaborative research and development activities. Expenses we incur related to collaborative research and development agreements approximate the revenue recognized under these agreements. Research and development costs are expensed as incurred. Research and development costs consist of salaries and benefits, including associated stock-based compensation, laboratory supplies and facility costs, as well as fees paid to other entities that conduct certain research and development activities on our behalf. We estimate preclinical study and clinical trial expenses based on the services performed pursuant to contracts with research institutions, CROs, and CMOs that conduct and manage preclinical studies and clinical trials on our behalf based on actual time and expenses incurred by them. Further, we accrue expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. We monitor patient enrollment levels and related activity to the extent reasonably possible and adjust estimates accordingly. If we do not identify costs that we have begun to incur or if we underestimate or overestimate the level of services performed or the costs of these services, our actual expenses could differ from our estimates. To date, we have not experienced significant changes in our estimates of preclinical studies and clinical trial accruals. We expense payments for the acquisition and development of technology as research and development costs if, at the time of payment, the technology: is under development; is not approved by the U.S. Food and Drug Administration or other regulatory agencies for marketing; has not reached technical feasibility; or otherwise has no foreseeable alternative future use.
Stock-Based Compensation	Stock-Based Compensation We recognize compensation expense using a fair-value-based method for costs related to all share-based payments, including restricted stock and stock options. For restricted stock awards, or RSAs, stock-based compensation cost related to employees and directors is based on the closing market value of our common stock at the date of grant and is recognized as expense ratably over the requisite service period. For stock option awards, stock-based compensation cost related to employees and directors is measured at the grant date, based on the fair-value-based measurement of the award estimated using the Black-Scholes option-pricing model, and is recognized as expense over the requisite service period on a straight-line basis. We are required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. We use historical data to estimate pre-vesting option forfeitures and record stock-based compensation expense only for those awards that we expect to vest. Restricted stock awards granted to individual service providers who are not employees or directors are accounted for at fair value by remeasuring the cost based on the closing stock price at the end of that reporting period. Options granted to individual service providers who are not employees or directors are accounted for at estimated fair value using the Black-Scholes option-pricing model and are subject to periodic remeasurement over the period during which the services are rendered.
Income Taxes	Income Taxes We account for income taxes using the liability method, under which deferred tax assets and liabilities are determined based on differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Our income tax benefit for 2016 relates to our ability to carry back 2016 losses to the 2015 tax year and to obtain a refund of taxes paid related to a prior period. Valuation allowances are provided when the expected realization of the deferred tax assets does not meet the more-likely-than-not criteria. As a result, deferred tax assets at the end of 2016 are subject to a full valuation allowance. We are required to determine whether it is more likely than not that a tax position will be sustained upon examination by the appropriate taxing authorities before any part of the benefit can be recorded in the financial statements. It is our practice to recognize interest and penalties related to unrecognized tax benefits, if any, as a component of income tax expense.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers: Topic 606 In March, April, May and December 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations , ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing , ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients to provide supplemental adoption guidance and clarification to ASU 2014-09 and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers . The effective date for these new standards is the same as the effective date and transition requirements for ASU 2014-09. We expect to adopt ASU 2014-09 in the first quarter of 2018 using the modified retrospective method. The adoption of ASU 2014-09 may have a material effect on our financial statements. To date, we have derived our revenues from license and collaboration agreements. The consideration we are eligible to receive under these agreements includes upfront payments, research and development funding, milestone payments and royalties. Each license and collaboration agreement is unique and will need to be assessed separately under the five-step process under the new standard. We have started our preliminary assessment of our active license and collaboration agreements. We expect that our evaluation of the accounting for collaboration agreements under the new revenue standard could identify material changes from the current accounting treatment. ASU 2014-09 differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments. Under our current accounting policy, we recognize milestone revenue using the milestone method specified in ASC 605-28, which generally results in the recognition of the milestone payment as revenue in the period that the milestone is achieved. However, under the new accounting standard, it is possible to start to recognize milestone revenue before the milestone is achieved, subject to management’s assessment of whether it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. In addition, the current accounting standards include a presumption that revenue from up-front non-refundable fees would be recognized ratably over the performance period, unless another attribution method was determined to more closely approximate the delivery of the goods or services to the customer. The new accounting standard does not have a presumption that entities would default to a ratable attribution approach and will require entities to determine an appropriate attribution method using either output or input methods. As such, the amount and timing of revenue recognition for our license and collaboration agreements may change under the new revenue standard. In February 2016, FASB issued ASU 2016-02, Leases. all annual and interim reporting periods thereafter. E In March 2016, FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting This standard makes several modifications to Topic 718 related to the accounting for forfeitures, employer tax withholding on share-based compensation and the financial statement presentation of excess tax benefits or deficiencies. ASU 2016-09 also clarifies the statement of cash flows presentation for certain components of share-based awards. The We expect to adopt ASU 2016-09 in the first quarter of 2017 and are evaluating the impact that the adoption of ASU 2016-09 will have on our consolidated financial statements and related disclosures.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
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): December 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 432 $ 432 $ — $ — U.S. Treasury securities 414,095 414,095 — — Certificate of deposit 1,543 — 1,543 — Total $ 416,070 $ 414,527 $ 1,543 $ — December 31, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 34,821 $ 34,821 $ — $ — U.S. Treasury securities 477,125 477,125 — — Total $ 511,946 $ 511,946 $ — $ —

Cash Equivalents and Marketab23

Cash Equivalents and Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2016
Cash And Cash Equivalents [Abstract]
Summary of Cash Equivalents and Marketable Securities	The following is a summary of our cash equivalents and marketable securities at December 31, 2016 and 2015 (in thousands): December 31, 2016 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 432 $ — $ — $ 432 U.S. Treasury securities 414,134 54 (93 ) 414,095 414,566 54 (93 ) 414,527 Less: cash equivalents (432 ) — — (432 ) Total marketable securities $ 414,134 $ 54 $ (93 ) $ 414,095 December 31, 2015 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 34,821 $ — $ — $ 34,821 U.S. Treasury securities 477,239 13 (127 ) 477,125 512,060 13 (127 ) 511,946 Less: cash equivalents (144,470 ) — 19 (144,451 ) Total marketable securities $ 367,590 $ 13 $ (108 ) $ 367,495
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	As of December 31, 2016, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Estimated Amortized Fair Cost Value Debt securities maturing: In one year or less $ 402,644 $ 402,619 In one to two years 11,490 11,476 Total marketable securities $ 414,134 $ 414,095

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Components of Property and Equipment	Property and equipment consist of the following (in thousands): December 31, 2016 2015 Computer equipment and software $ 1,467 $ 1,399 Furniture and fixtures 804 804 Laboratory equipment 14,853 11,887 Leasehold improvements 2,468 2,396 19,592 16,486 Less: accumulated depreciation and amortization (13,385 ) (11,947 ) Property and equipment, net $ 6,207 $ 4,539

Other Accrued Liabilities (Tabl

Other Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2016
Payables And Accruals [Abstract]
Schedule of Other Accrued Liabilities	Other accrued liabilities consist of the following (in thousands): December 31, 2016 2015 Clinical development $ 6,831 $ 1,966 Manufacturing 4,463 333 Trade Payable 3,729 3,252 Other 412 331 Total accrued liabilities $ 15,435 $ 5,882

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Option Activity under Stock Plans and Related Information	The following table summarizes option activity under our stock plans and related information: Options Outstanding Weighted- Weighted- Average Average Exercise Remaining Aggregate Number Price Contractual Intrinsic of Shares Per Share Terms Value (in years) (in thousands) Balance at January 1, 2016 3,028,714 $ 12.62 Options granted 1,448,850 $ 44.32 Options exercised (884,139 ) $ 7.74 Options forfeited (138,958 ) $ 21.44 Options expired (128 ) $ 18.37 Balance at December 31, 2016 3,454,339 $ 26.80 Options exercisable at December 31, 2016 1,308,431 $ 13.73 6.44 $ 47,603 Options vested and expected to vest at December 31, 2016 3,399,919 $ 26.95 8.08 $ 79,094
Schedule of Restricted Stock Award Activity under Stock Plans and Related Information	The following table summarizes the RSAs activity under our stock plans and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at January 1, 2016 1,574,870 $ 19.71 RSAs granted 395,430 $ 42.75 RSAs vested (800,554 ) $ 19.04 RSAs forfeited (128,817 ) $ 20.87 Unvested balance at December 31, 2016 1,040,929 $ 28.84
Schedule of Stock-Based Compensation Expenses Recognized	Total stock-based compensation expense recognized was as follows: Year Ended December 31, (in thousands) 2016 2015 2014 Research and development $ 17,960 $ 6,362 $ 1,761 General and administrative 14,925 5,105 1,657 Total $ 32,885 $ 11,467 $ 3,418
Schedule of Stock Option Weighted-Average Assumptions	We estimated the fair value of each award using the Black-Scholes option-pricing model based on the date of grant of such award with the following assumptions: Options ESPP Year Ended December 31, Year Ended December 31, 2016 2015 2014 2016 2015 2014 Expected term (years) 5.5-6.3 5.5-6.1 5.3-6.7 0.5 0.5 0.5 Expected volatility 69.0-74.0% 71.0-76.0% 85.0% 47.0-57.0% 75.0-96.0% 49.0-83.0% Risk-free interest rate 1.3-1.8% 1.4-1.9% 1.6-2.0% 0.4-0.6% 0.1-0.3% 0.1% Expected dividend yield 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Income (Loss)	The following table sets forth the computation of basic and diluted net income (loss) (in thousands, except per share data): Year Ended December 31, 2016 2015 2014 Numerator: Net income (loss) $ (65,697 ) $ 249,647 $ (37,424 ) Denominator: Denominator for basic income (loss) per share - weighted-average shares 26,955 25,661 20,865 Effect of dilutive securities: Equity incentive plans — 1,374 — Denominator for diluted income (loss) per share 26,955 27,035 20,865 Income (loss) per share - Basic $ (2.44 ) $ 9.73 $ (1.79 ) Income (loss) per share - Diluted $ (2.44 ) $ 9.23 $ (1.79 )
Securities Excluded from Calculation of Diluted Net Income (Loss) Per Share	We excluded the following securities from the calculation of diluted net income (loss) per share as the effect would have been antidilutive (in thousands): Year Ended December 31, 2016 2015 2014 Options to purchase common stock 2,981 187 2,379 RSAs 1,278 8 9 4,259 195 2,388

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax (Benefit) Expense	The components of our income tax (benefit) expense were as follows: Year Ended December 31, 2016 2015 2014 Current tax (benefit) expense Federal $ (40,740 ) $ 47,369 $ — State (5,340 ) 5,473 — Total current (benefit) expense (46,080 ) 52,842 — Deferred tax (benefit) expense Federal 15,032 (15,032 ) — State — — — Total deferred tax (benefit) expense 15,032 (15,032 ) — Total tax (benefit) expense $ (31,048 ) $ 37,810 $ —
Schedule of Income Tax (Benefit) Expense Differs from Amount Computed by Applying Statutory Federal Income Tax Rate	The income tax (benefit) expense differs from the amount computed by applying the statutory federal income tax rate as follows (in thousands) Year Ended December 31, 2016 2015 2014 Federal statutory income tax $ (33,862 ) $ 100,610 $ (13,098 ) State statutory income tax (3,471 ) 3,558 — Nondeductible stock compensation 715 437 (501 ) Nontaxable equity premiums (248 ) (443 ) (504 ) Deferred tax assets (utilized) not benefitted 12,152 (62,705 ) 14,075 Research and orphan drug credits (8,029 ) (3,846 ) — Other permanent items 1,695 199 28 Income tax (benefit) expense $ (31,048 ) $ 37,810 $ —
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets consist of the following (in thousands): As of December 31, 2016 2015 Net operating loss carryforwards $ 5,615 $ 941 Research and orphan drug credits 18,182 819 Deferred revenue 10,939 16,697 Stock based compensation 6,908 4,542 Capitalized license and depreciation basis differences 3,574 3,685 Reserves and accruals 1,736 3,960 Total deferred tax assets 46,954 30,644 Less: valuation allowance (46,954 ) (15,573 ) Net deferred tax assets $ — $ 15,071
Schedule of Reconciliation of Unrecognized Tax Benefits	A reconciliation of our unrecognized tax benefits for the years ended December 31, 2016, 2015 and 2014 Unrecognized Income Tax Benefits Balance as of December 31, 2013 $ 1,781 Additions for prior year tax positions 11 Additions for current year tax positions 445 Balance as of December 31, 2014 2,237 Additions for prior year tax positions 615 Additions for current year tax positions 580 Balance as of December 31, 2015 3,432 Additions for prior year tax positions 4,394 Additions for current year tax positions 1,577 Balance as of December 31, 2016 $ 9,403

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Schedule of Estimated Future Minimum Commitments for Non-cancelable Operating Leases	The estimated future minimum commitments under our non-cancelable operating leases are as follows (in thousands): Year ending December 31: 2017 3,461 2018 5,092 2019 7,025 2020 7,274 2021 7,524 Thereafter 51,017 Total estimated minimum payments $ 81,393

Selected Quarterly Financial 30

Selected Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Information	The following amounts are in thousands, except per share amounts: Quarter Ended March 31, June 30, September 30, December 31, Quarterly Results of Operations 2016 2016 2016 2016 (Unaudited) Revenue $ 6,520 $ 9,229 $ 6,680 $ 8,262 Net loss (13,040 ) (13,137 ) (19,414 ) (20,106 ) Basic and diluted net loss per share (0.49 ) (0.49 ) (0.72 ) (0.73 ) Quarter Ended March 31, June 30, September 30, December 31, Quarterly Results of Operations 2015 2015 2015 2015 (Unaudited) Revenue $ 4,287 $ 6,315 $ 5,858 $ 363,341 (1) Net income (loss) (11,036 ) (11,474 ) (23,971 ) 296,128 Basic net income (loss) per share (0.44 ) (0.45 ) (0.93 ) 11.37 Diluted net income (loss) per share (0.44 ) (0.45 ) (0.93 ) 10.63 (1) Includes the $350.0 million upfront license fee from the cabiralizumab collaboration agreement. See Note 9 for further discussion.

Business - Additional Informati

Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment	1

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Summary of Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets
U.S. Treasury securities	$ 414,095	$ 367,495
Total	416,070	511,946
Money market funds [Member]
Assets
Cash equivalents	432	34,821
U.S. Treasury securities	432	34,821
Certificate of deposit [Member]
Assets
Cash equivalents	1,543
U.S. Treasury securities [Member]
Assets
U.S. Treasury securities	414,095	477,125
Level 1 [Member]
Assets
Total	414,527	511,946
Level 1 [Member] | Money market funds [Member]
Assets
Cash equivalents	432	34,821
Level 1 [Member] | U.S. Treasury securities [Member]
Assets
U.S. Treasury securities	414,095	$ 477,125
Level 2 [Member]
Assets
Total	1,543
Level 2 [Member] | Certificate of deposit [Member]
Assets
Cash equivalents	$ 1,543

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)
Summary Of Significant Accounting Policies [Line Items]
Impairment losses on long lived assets	$ 0
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	5 years

Cash Equivalents and Marketab34

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 414,134	$ 367,590
Unrealized Gains	54	13
Unrealized Losses	(93)	(108)
Estimated Fair Value	414,095	367,495
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	432	34,821
Estimated Fair Value	432	34,821
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	414,134	477,239
Unrealized Gains	54	13
Unrealized Losses	(93)	(127)
Estimated Fair Value	414,095	477,125
Marketable securities including cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	414,566	512,060
Unrealized Gains	54	13
Unrealized Losses	(93)	(127)
Estimated Fair Value	414,527	511,946
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	(432)	(144,470)
Unrealized Losses		19
Estimated Fair Value	$ (432)	$ (144,451)

Cash Equivalents and Marketab35

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	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 414,134	$ 367,590
Total marketable securities, Estimated Fair Value	414,095	367,495
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, In one year or less	402,644
Amortized Cost, In one to two years	11,490
Amortized Cost Basis	414,134	477,239
Estimated Fair Value, In one year or less	402,619
Estimated Fair Value, In one to two years	11,476
Total marketable securities, Estimated Fair Value	$ 414,095	$ 477,125

Cash Equivalents and Marketab36

Cash Equivalents and Marketable Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on marketable securities	$ 93,000
Sales of available-for-sale securities	$ 0
Cash equivalents and marketable securities average maturity period	4 months
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and marketable securities maturity period	13 months

Property and Equipment - Compon

Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 19,592	$ 16,486
Less: accumulated depreciation and amortization	(13,385)	(11,947)
Property and equipment, net	6,207	4,539
Computer equipment and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,467	1,399
Furniture and fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	804	804
Laboratory equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	14,853	11,887
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 2,468	$ 2,396

Other Accrued Liabilities - Sch

Other Accrued Liabilities - Schedule of Other Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Clinical development	$ 6,831	$ 1,966
Manufacturing	4,463	333
Trade Payable	3,729	3,252
Other	412	331
Total accrued liabilities	$ 15,435	$ 5,882

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	Sep. 23, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional awards granted	0
Nonstatutory stock options granted, exercise price percentage		85.00%
Stock options granted to a stockholder owning more than 10%, exercise price percentage		110.00%
Stock options granted, expiration term		10 years
Options vesting period		4 years
Weighted-average grant-date fair value per share of stock options granted		$ 27.95	$ 14.18	$ 8.39
Total intrinsic value of options exercised		$ 30,800,000	$ 10,000,000	$ 4,200,000
Total unrecognized compensation expense related to unvested employee and director stock options, net of forfeitures		$ 39,800,000
Unrecognized compensation expense expected to recognize, weighted-average period		2 years 10 months 24 days
Expected dividend yield		0.00%
Employees and directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 11,100,000	4,500,000	2,900,000
Non employee options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 309,000	266,000	134,000
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense expected to recognize, weighted-average period		1 year 1 month 6 days
Total fair value of share vesting		$ 33,200,000	42,000	54,000
Total unrecognized compensation expense to unvested RSAs, net of forfeitures		15,900,000
Restricted Stock Awards [Member] | Employees and directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		20,200,000	6,200,000	0
Restricted Stock Awards [Member] | Non employee options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 673,000	85,000	0
Restricted Stock Awards [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period		1 year 6 months
Restricted Stock Awards [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period		3 years
2013 Omnibus Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for issuance		3,500,000
Percent of annual increase in common stock available for issuance		4.00%
Number of shares of common stock reserved for future issuance		1,340,666
Prior Plans [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for issuance		1,069,985
2013 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for issuance		714,951
Percent of annual increase in common stock available for issuance		1.00%
Number of shares of common stock reserved for future issuance		250,000
Maximum increase in shares reserved for issuance		300,000
Common stock available for issuance, description		Unless our Board provides otherwise, beginning on January 1, 2014 and continuing until the expiration of the ESPP, the total number of shares of common stock available for issuance under the ESPP will automatically increase annually on January 1 by the lesser of (i) 1% of the total number of issued and outstanding shares of common stock as of December 31 of the immediately preceding year, or (ii) 300,000 shares of common stock. As of December 31, 2016, 714,951 shares of common stock were available for issuance under the ESPP.
Unrecognized compensation expense expected to recognize, weighted-average period		4 years 6 months
Stock-based compensation expense		$ 602,000	$ 455,000	$ 339,000
Purchase price per share as a percentage of fair market value of our common stock		85.00%
Shares issued under ESPP		45,647
Total unrecognized compensation expense		$ 253,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Option Activity under Stock Plans and Related Information (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance | shares	3,028,714
Number of Shares, Options granted | shares	1,448,850
Number of Shares, Options exercised | shares	(884,139)
Number of Shares, Options forfeited | shares	(138,958)
Number of Shares, Options expired | shares	(128)
Number of Shares, Ending balance | shares	3,454,339
Number of Shares, Options exercisable | shares	1,308,431
Number of Shares, Options vested and expected to vest | shares	3,399,919
Weighted-Average Exercise Price Per Share, Options beginning balance | $ / shares	$ 12.62
Weighted-Average Exercise Price Per Share, Options granted | $ / shares	44.32
Weighted-Average Exercise Price Per Share, Options exercised | $ / shares	7.74
Weighted-Average Exercise Price Per Share, Options forfeited | $ / shares	21.44
Weighted-Average Exercise Price Per Share, Options expired | $ / shares	18.37
Weighted-Average Exercise Price Per Share, Options ending balance | $ / shares	26.80
Weighted-Average Exercise Price Per Share, Options exercisable | $ / shares	13.73
Weighted-Average Exercise Price Per Share, Options vested and expected to vest | $ / shares	$ 26.95
Weighted-Average Remaining Contractual Terms, Options exercisable	6 years 5 months 9 days
Weighted-Average Remaining Contractual Terms, Options vested and expected to vest	8 years 29 days
Aggregate Intrinsic Value, Options exercisable | $	$ 47,603
Aggregate Intrinsic Value, Options vested and expected to vest | $	$ 79,094

Stockholders' Equity - Schedu41

Stockholders' Equity - Schedule of Restricted Stock Award Activity under Stock Plans and Related Information (Detail) - Restricted Stock Awards [Member]	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Unvested, Beginning balance | shares	1,574,870
Granted, Number of Shares | shares	395,430
Vested, Number of Shares | shares	(800,554)
Forfeited, Number of Shares | shares	(128,817)
Number of Shares, Unvested, Ending balance | shares	1,040,929
Shares, Weighted-Average Grant-Date Fair Value balance at January 1, 2016 | $ / shares	$ 19.71
Shares Granted, Weighted-Average Grant-Date Fair Value | $ / shares	42.75
Shares Vested, Weighted-Average Grant-Date Fair Value | $ / shares	19.04
Shares Forfeited, Weighted-Average Grant-Date Fair Value | $ / shares	20.87
Shares, Weighted-Average Grant-Date Fair Value balance at December 31, 2016 | $ / shares	$ 28.84

Stockholders' Equity - Schedu42

Stockholders' Equity - Schedule of Stock-Based Compensation Expenses Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 32,885	$ 11,467	$ 3,418
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	17,960	6,362	1,761
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 14,925	$ 5,105	$ 1,657

Stockholders' Equity - Schedu43

Stockholders' Equity - Schedule of Stock Option Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield	0.00%
Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility			85.00%
Risk-free interest rate, minimum	1.30%	1.40%	1.60%
Risk-free interest rate, maximum	1.80%	1.90%	2.00%
Expected dividend yield	0.00%	0.00%	0.00%
Options [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	5 years 6 months	5 years 3 months 18 days
Expected volatility	69.00%	71.00%
Options [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 3 months 18 days	6 years 1 month 6 days	6 years 8 months 12 days
Expected volatility	74.00%	76.00%
ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 months	6 months	6 months
Risk-free interest rate			0.10%
Risk-free interest rate, minimum	0.40%	0.10%
Risk-free interest rate, maximum	0.60%	0.30%
Expected dividend yield	0.00%	0.00%	0.00%
ESPP [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	47.00%	75.00%	49.00%
ESPP [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	57.00%	96.00%	83.00%

Earnings per Share - Computatio

Earnings per Share - Computation of Basic and Diluted Net Income (Loss) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income (loss)	$ (20,106)	$ (19,414)	$ (13,137)	$ (13,040)	$ 296,128	$ (23,971)	$ (11,474)	$ (11,036)	$ (65,697)	$ 249,647	$ (37,424)
Denominator:
Denominator for basic income (loss) per share - weighted-average shares									26,955	25,661	20,865
Effect of dilutive securities:
Equity incentive plans										1,374
Denominator for diluted income (loss) per share									26,955	27,035	20,865
Income (loss) per share - Basic					$ 11.37	$ (0.93)	$ (0.45)	$ (0.44)	$ (2.44)	$ 9.73	$ (1.79)
Income (loss) per share - Diluted					$ 10.63	$ (0.93)	$ (0.45)	$ (0.44)	$ (2.44)	$ 9.23	$ (1.79)

Earnings per Share - Securities

Earnings per Share - Securities Excluded from Calculation of Diluted Net Income (Loss) Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net income (loss) per share	4,259	195	2,388
Options to purchase common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net income (loss) per share	2,981	187	2,379
RSAs [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net income (loss) per share	1,278	8	9

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Eligible employees contribution percentage	100.00%
Defined contribution plan, employer matching contribution, percent of match	50.00%	50.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay		4.00%
Defined contribution plan, employer matching contribution, amount	$ 6,000	$ 6,000
Defined contribution plan, employer matching contribution, shares		17,803
Defined contribution plan, company matching contribution expense	$ 712,000	$ 477,000

Collaborative Research and De47

Collaborative Research and Development Agreements - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Apr. 30, 2014	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 14, 2015
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate purchase price						$ 78,693,000	$ 58,728,000
Cabiralizumab Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront payment				$ 350,000,000
Bristol-Myers Squibb Company [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized for development and regulatory milestone payments					$ 0
Upfront agreement fee, receivable		$ 30,000,000
Termination of refundable upfront fee					30,000,000
Revenue recognized from upfront fee					5,900,000	6,400,000
Deferred revenue recognized under collaboration arrangement	$ 23,600,000			23,600,000	$ 17,700,000	23,600,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License and collaboration agreement entered date					Oct. 14, 2015
Research funding received					$ 8,000,000	200,000
Received upfront payment	350,000,000
Recognized revenue under collaboration arrangement	350,000,000				14,400,000	359,900,000
Bristol-Myers Squibb Company [Member] | Oncology Indications [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development and regulatory milestone payments								$ 1,050,000,000
Bristol-Myers Squibb Company [Member] | Non-Oncology Indications [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development and regulatory milestone payments								$ 340,000,000
Bristol-Myers Squibb Company [Member] | Immuno-oncology collaboration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront payment			$ 20,000,000
Recognized revenue under collaboration arrangement					7,700,000	7,000,000	6,000,000
Deferred revenue recognized under collaboration arrangement					2,400,000
Research funding expected to receive over the initial three-year research term					$ 9,500,000
Research agreement, initial term					3 years
Research agreement additional term					2 years
Research agreement additional term description					BMS may extend the research term for two additional one-year periods on a year-by-year basis
Research agreement, initial expiration period					2017-03
Research agreement extended period end					2018-03
Research agreement additional term option exercised, description					In December 2016, BMS exercised its option to extend the research term for an additional year to March 2018.
Research agreement remaining option to extend additional term description					BMS has the option to extend the research term for one additional year.
Research agreement option to additional extend term					1 year
Research agreement term					5 years
Research funding payment received					$ 1,600,000	4,100,000	$ 3,400,000
Issuance of stock, Shares					994,352
Price per share					$ 21.16
Aggregate purchase price					$ 21,000,000
Deferred revenue relating to collaboration agreement	$ 16,800,000			$ 16,800,000	$ 10,600,000	$ 16,800,000

Collaborative Research and De48

Collaborative Research and Development Agreements - Additional Information 1 (Detail) - USD ($)

1 Months Ended

12 Months Ended

Jan. 31, 2016

Sep. 30, 2014

Oct. 31, 2013

Sep. 30, 2013

Apr. 30, 2012

Mar. 31, 2011

Aug. 31, 2010

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Dec. 31, 2012

Dec. 31, 2011

May 31, 2011

Glaxo Smith Kline LLC [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Research funding payment received

$ 700,000

Increase the research funding

$ 700,000

Extend research terms

3 months

Extend research date

2016-07

Glaxo Smith Kline LLC [Member] | Respiratory Diseases Discovery Collaboration [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Received upfront payment

$ 7,500,000

Research funding

$ 10,500,000

Research funding payment received

$ 2,000,000

Deferred revenue recognized under collaboration arrangement

1,700,000

Research funding received

3,600,000

3,900,000

$ 3,900,000

Recognized revenue under collaboration arrangement

$ 5,000,000

7,300,000

6,400,000

Glaxo Smith Kline LLC [Member] | Respiratory Diseases Discovery Collaboration [Member] | Series A-3 convertible preferred stock [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Convertible preferred stock issued

381,693

Convertible preferred stock price per share

$ 26.20

Proceeds from issuance of preferred stock

$ 10,000,000

Deferred revenue recognized under collaboration arrangement

3,100,000

Glaxo Smith Kline LLC [Member] | Track 1 Target, Respiratory Diseases Discovery Collaboration [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Eligible to receive potential target evaluation and selection fees and contingent payments

124,300,000

Glaxo Smith Kline LLC [Member] | Track 2 Target, Respiratory Diseases Discovery Collaboration [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Eligible to receive potential target evaluation and selection fees and contingent payments

193,800,000

Glaxo Smith Kline LLC [Member] | FP-1039 License and Collaboration [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under collaboration arrangement

$ 21,000

$ 100,000

100,000

Termination license agreement effective date

Sep. 5, 2016

Notice period of termination of license agreement

180 days

Glaxo Smith Kline LLC [Member] | Muscle Disorders Discovery Collaboration [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Received upfront payment

$ 7,000,000

Research funding

$ 6,300,000

Recognized revenue under collaboration arrangement

$ 3,400,000

Research agreement, initial term

3 years

Milestone payments received

$ 300,000

$ 300,000

Extension fee

$ 200,000

Extended evaluation period

8 months

Proceeds from options exercised

$ 1,500,000

Glaxo Smith Kline LLC [Member] | Muscle Disorders Discovery Collaboration [Member] | Maximum [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Option and selection payments

$ 1,800,000

Glaxo Smith Kline LLC [Member] | Muscle Disorders Discovery Collaboration [Member] | Series A-2 convertible preferred stock [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Convertible preferred stock issued

329,597

Convertible preferred stock price per share

$ 22.76

Proceeds from issuance of preferred stock

$ 7,500,000

Deferred revenue recognized under collaboration arrangement

$ 3,000,000

FP-1039 License and Collaboration [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Received upfront payment

$ 50,000,000

Recognized revenue under collaboration arrangement

$ 50,000,000

Collaborative Research and De49

Collaborative Research and Development Agreements - Additional Information 2 (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Bluebird bio, Inc. License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront payment			$ 1.5
Recognized revenue under collaboration arrangement			1.5
Termination license agreement effective date		May 17, 2017
Notice period of termination of license agreement		120 days
Fibrosis and CNS Collaboration [Member] | UCB Pharma S.A. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront payment	$ 6
Technology access fee	6.6
Research funding	$ 2
Research agreement term	5 years
Received target evaluation and selection fees		$ 0.4	0.1
Recognized revenue under collaboration arrangement		3.5	4	$ 3.2
Deferred revenue relating to collaboration agreement		$ 3.7	$ 6.7
Expected evaluation period to complete initial research activities		2 years
Fibrosis and CNS Collaboration [Member] | UCB Pharma S.A. [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Eligible cash receipt for target evaluation and selection		$ 0.4

Acquired Technologies - Additio

Acquired Technologies - Additional Information (Detail) $ in Thousands	1 Months Ended		12 Months Ended
	Jul. 31, 2015USD ($)	Dec. 31, 2011USD ($)Installment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development expense related to license agreement			$ 94,072	$ 70,197	$ 43,173
Inhibrx [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront fee paid for license and services	$ 10,000
Milestone payment method description			Additionally, with respect to each licensed therapeutic product, we will be obligated to pay up to $62.5 million in specified development milestone payments and (i) if such licensed therapeutic product does not receive a Breakthrough Therapy Designation from the FDA up to $280.0 million in specified regulatory and commercial milestone payments, or (ii) if such licensed therapeutic product receives a Breakthrough Therapy Designation from the FDA, up to $380.0 million in specified regulatory and commercial milestone payments. Inhibrx is also eligible for low double-digit tiered royalties on future product sales. We may pay all or a portion of milestone payments for development and regulatory events in shares of our common stock, subject to certain limitations and conditions. We would be obligated to register for resale under the Securities Act any such shares of our common stock.
Research and development expense related to license agreement	8,000
Defer and capitalize amount related to prepayment of research and development cost	2,000		$ 1,000	1,000
Inhibrx [Member] | Maximum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration Fee, Payable	62,500
Inhibrx [Member] | Not Receives Breakthrough Therapy Designation [Member] | Maximum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Estimated regulatory and commercial milestone payments	280,000
Inhibrx [Member] | Receives Breakthrough Therapy Designation [Member] | Maximum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Estimated regulatory and commercial milestone payments	$ 380,000
Galaxy Biotech, LLC [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront license payment		$ 3,000
Number of installments | Installment		2
Milestone payment			$ 2,500	$ 0	$ 2,600

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax [Line Items]
Income tax expense (benefit)	$ (31,048,000)	$ 37,810,000	$ 0
Increase (decrease) in valuation allowance	31,400,000	(74,100,000)
Unrecognized tax benefits	9,403,000	3,432,000	$ 2,237,000	$ 1,781,000
Significant increases or decreases expected to uncertain tax positions within next 12 months	0
Accrued interest or penalties	0	$ 0
Incurred interest and penalties	$ 0
Ongoing tax examinations by tax authorities	We have no ongoing tax examinations by tax authorities at this time.
State tax authority [Member]
Income Tax [Line Items]
Operating losses available for future use	$ 145,100,000
Operating losses available for future use, Expiration date	Dec. 31, 2017
Tax credits available to offset future tax	$ 12,300,000
Federal tax authority [Member] | Research and orphan drug credits [Member]
Income Tax [Line Items]
Tax credits available to offset future tax	$ 17,200,000
Tax credit carryforwards, Expiration date	Dec. 31, 2023

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Tax (Benefit) Expense (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current tax (benefit) expense
Federal	$ (40,740,000)	$ 47,369,000
State	(5,340,000)	5,473,000
Total current (benefit) expense	(46,080,000)	52,842,000
Deferred tax (benefit) expense
Federal	15,032,000	(15,032,000)
Total deferred tax (benefit) expense	15,032,000	(15,032,000)
Income tax (benefit) expense	$ (31,048,000)	$ 37,810,000	$ 0

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax (Benefit) Expense Differs from Amount Computed by Applying Statutory Federal Income Tax Rate (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Abstract]
Federal statutory income tax	$ (33,862,000)	$ 100,610,000	$ (13,098,000)
State statutory income tax	(3,471,000)	3,558,000
Nondeductible stock compensation	715,000	437,000	(501,000)
Nontaxable equity premiums	(248,000)	(443,000)	(504,000)
Deferred tax assets (utilized) not benefitted	12,152,000	(62,705,000)	14,075,000
Research and orphan drug credits	(8,029,000)	(3,846,000)
Other permanent items	1,695,000	199,000	28,000
Income tax (benefit) expense	$ (31,048,000)	$ 37,810,000	$ 0

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets Liabilities Net [Abstract]
Net operating loss carryforwards	$ 5,615	$ 941
Research and orphan drug credits	18,182	819
Deferred revenue	10,939	16,697
Stock based compensation	6,908	4,542
Capitalized license and depreciation basis differences	3,574	3,685
Reserves and accruals	1,736	3,960
Total deferred tax assets	46,954	30,644
Less: valuation allowance	(46,954)	(15,573)
Net deferred tax assets	$ 0	$ 15,071

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Beginning Balance	$ 3,432	$ 2,237	$ 1,781
Additions for prior year tax positions	4,394	615	11
Additions for current year tax positions	1,577	580	445
Ending Balance	$ 9,403	$ 3,432	$ 2,237

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Leased Assets [Line Items]
Lease expiration		Dec. 31, 2017
Deferred rent	$ 900,000	$ 900,000	$ 1,600,000
Incentive to lessee	1,900,000	1,900,000
Unamortized leasehold improvement incentive total	$ 300,000	300,000	600,000
Rent expense		$ 2,300,000	$ 2,300,000	$ 1,900,000
New Lease [Member]
Operating Leased Assets [Line Items]
Lease term	10 years
Lease option additional extend term	5 years
Additional lease requirements		The new lease required us to deliver an irrevocable standby letter of credit in an amount of $1.5 million to landlord for the period commencing on the effective date of the agreement until at least 60 days after the expiration of the new lease, subject to 50% reduction on the first day of the sixth lease year if certain conditions are met.
Reduction in rent expense percentage	50.00%
New Lease [Member] | Irrevocable Standby Letter of Credit [Member]
Operating Leased Assets [Line Items]
Letter of credit	$ 1,500,000	$ 1,500,000
New Lease [Member] | Maximum [Member]
Operating Leased Assets [Line Items]
Allowance for cost of leasehold improvements	$ 14,400,000	$ 14,400,000

Commitments and Contingencies57

Commitments and Contingencies - Schedule of Estimated Future Minimum Commitments for Non-cancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Leases Operating [Abstract]
2,017	$ 3,461
2,018	5,092
2,019	7,025
2,020	7,274
2,021	7,524
Thereafter	51,017
Total estimated minimum payments	$ 81,393

Selected Quarterly Financial 58

Selected Quarterly Financial Information - Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 8,262	$ 6,680	$ 9,229	$ 6,520	$ 363,341	$ 5,858	$ 6,315	$ 4,287
Net income (loss)	$ (20,106)	$ (19,414)	$ (13,137)	$ (13,040)	$ 296,128	$ (23,971)	$ (11,474)	$ (11,036)	$ (65,697)	$ 249,647	$ (37,424)
Basic and diluted net loss per share	$ (0.73)	$ (0.72)	$ (0.49)	$ (0.49)
Income (loss) per share - Basic					$ 11.37	$ (0.93)	$ (0.45)	$ (0.44)	$ (2.44)	$ 9.73	$ (1.79)
Income (loss) per share - Diluted					$ 10.63	$ (0.93)	$ (0.45)	$ (0.44)	$ (2.44)	$ 9.23	$ (1.79)

Selected Quarterly Financial 59

Selected Quarterly Financial Information - Summary of Quarterly Financial Information (Parenthetical) (Detail) $ in Millions	3 Months Ended
	Dec. 31, 2015USD ($)
Cabiralizumab Collaboration Agreement [Member]
Received upfront payment	$ 350