Five Prime Therapeutics (FPRX) 10-K 22 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 15, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	FPRX
Entity Registrant Name	Five Prime Therapeutics, Inc.
Entity Central Index Key	0001175505
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	true
ICFR Auditor Attestation Flag	true
Entity File Number	001-36070
Entity Tax Identification Number	26-0038620
Entity Address, Address Line One	111 Oyster Point Boulevard
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	415
Local Phone Number	365-5600
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		46,572,029
Entity Public Float			$ 221.6
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 69,422	$ 55,800
Marketable securities	217,837	100,580
Receivables from collaborative partners	85	4,097
Prepaid and other current assets	5,064	6,243
Total current assets	292,408	166,720
Restricted cash	1,543	1,543
Property and equipment, net	11,209	22,534
Operating lease, right-of-use assets	21,276	30,934
Other long-term assets	5,214	2,411
Total assets	331,650	224,142
Current liabilities:
Accounts payable	473	1,184
Accrued personnel-related expenses	5,201	6,805
Other accrued liabilities	11,385	9,659
Operating lease obligations, current portion	5,125	4,080
Deferred revenue, current portion		1,296
Total current liabilities	22,184	23,024
Deferred revenue, long-term portion	2,057	5,113
Operating lease obligations, long-term portion	42,309	45,532
Commitments and contingencies (Note 13)
Stockholders’ equity:
Common stock, $0.001 par value; 100,000,000 shares authorized; 44,617,735 issued and 45,848,446 outstanding at December 31, 2020; 36,280,368 issued and 35,219,791 outstanding at December 31, 2019.	45	35
Preferred stock, $0.001 par value, 10,000,000 shares authorized; no shares issued and outstanding
Additional paid-in capital	781,291	582,243
Accumulated other comprehensive (loss) income	(25)	78
Accumulated deficit	(516,211)	(431,883)
Total stockholders’ equity	265,100	150,473
Total liabilities and stockholders’ equity	$ 331,650	$ 224,142

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
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	46,617,735	36,280,368
Common stock, shares outstanding	45,848,446	35,219,791
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Total revenue	$ 13,178	$ 14,874	$ 49,868
Operating expenses:
Research and development	65,491	114,063	156,352
General and administrative	40,557	42,749	39,671
Total operating expenses	106,048	156,812	196,023
Loss from operations	(92,870)	(141,938)	(146,155)
Other income, net	1,912	4,736	5,708
Loss before income tax	(90,958)	(137,202)	(140,447)
Income tax benefit	6,630
Net loss	$ (84,328)	$ (137,202)	$ (140,447)
Basic and diluted net loss per share	$ (2.29)	$ (3.92)	$ (4.13)
Weighted-average shares used to compute basic and diluted net loss per common share	36,834	34,970	33,976
Net loss	$ (84,328)	$ (137,202)	$ (140,447)
Other comprehensive (loss) gain:
Unrealized (loss) gain on marketable securities, net of tax	(103)	184	370
Comprehensive loss	(84,431)	(137,018)	(140,077)
Collaboration revenue [Member]
Revenue:
Total revenue	8,178	$ 14,874	$ 49,868
License revenue [Member]
Revenue:
Total revenue	$ 5,000

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	At-The-Market [Member]	Common Stock [Member]	Common Stock [Member]At-The-Market [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]At-The-Market [Member]	Accumulated Other Comprehensive Gain (Loss) [Member]	Retained Earnings (Accumulated Deficit) [Member]
Beginning Balance at Dec. 31, 2017	$ 265,202		$ 28		$ 421,257		$ (476)	$ (155,607)
Beginning Balance, Shares at Dec. 31, 2017			28,178,639
Issuance of common stock upon follow-on public offering	115,000		$ 6		114,994
Issuance of stock, Shares			5,897,435
Issuance costs related to follow-on public offering	(7,388)				(7,388)
Issuance of common stock under equity incentive plans	3,963				3,963
Issuance of common stock under equity incentive plans, Shares			821,456
Repurchase of shares to satisfy tax withholding obligations	(2,402)				(2,402)
Repurchase of shares to satisfy tax withholding obligations, Shares			(151,809)
Effect of adoption of Topic 606 | ASU 2016-09 [Member]	1,373							1,373
Stock-based compensation expense	29,468				29,468
Other comprehensive gain (loss)	370						370
Net loss	(140,447)							(140,447)
Ending Balance at Dec. 31, 2018	265,139		$ 34		559,892		(106)	(294,681)
Ending Balance, Shares at Dec. 31, 2018			34,745,721
Issuance of common stock under equity incentive plans	1,136		$ 1		1,135
Issuance of common stock under equity incentive plans, Shares			712,500
Repurchase of shares to satisfy tax withholding obligations	(1,599)				(1,599)
Repurchase of shares to satisfy tax withholding obligations, Shares			(238,430)
Stock-based compensation expense	22,815				22,815
Other comprehensive gain (loss)	184						184
Net loss	(137,202)							(137,202)
Ending Balance at Dec. 31, 2019	$ 150,473		$ 35		582,243		78	(431,883)
Ending Balance, Shares at Dec. 31, 2019	35,219,791		35,219,791
Issuance of common stock upon follow-on public offering	$ 163,447	$ 7,366	$ 8	$ 1	163,439	$ 7,365
Issuance of stock, Shares			8,280,000	1,394,933
Issuance costs related to follow-on public offering	(267)	$ (230)			(267)	$ (230)
Issuance of common stock under equity incentive plans	4,180		$ 1		4,179
Issuance of common stock under equity incentive plans, Shares			1,222,928
Repurchase of shares to satisfy tax withholding obligations	(2,352)				(2,352)
Repurchase of shares to satisfy tax withholding obligations, Shares			(269,206)
[Disgorgement of stockholder's short-swing profits]	16,727				16,727
Stock-based compensation expense	10,187				10,187
Other comprehensive gain (loss)	(103)						(103)
Net loss	(84,328)							(84,328)
Ending Balance at Dec. 31, 2020	$ 265,100		$ 45		$ 781,291		$ (25)	$ (516,211)
Ending Balance, Shares at Dec. 31, 2020	45,848,446		45,848,446

Statements of Cash Flows

Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (84,328,000)	$ (137,202,000)	$ (140,447,000)
Adjustments to reconcile net loss to net cash from operating activities:
Depreciation and amortization	3,196,000	5,313,000	5,020,000
Impairment of fixed assets	5,036,000	1,959,000
Amortization of right-of-use assets	2,705,000	2,351,000
Impairment of right-of-use assets	8,792,000
Write-off of right-of-use assets	394,000
Stock-based compensation expense	10,187,000	22,815,000	29,468,000
Amortization of discounts and premiums on marketable securities	(50,000)	(2,163,000)	(1,750,000)
(Gain) loss on disposal of property and equipment	(3,617,000)		38,000
Changes in operating assets and liabilities:
Receivables from collaborative partners	4,012,000	999,000	8,037,000
Prepaid, other current assets, and other long-term assets	(1,695,000)	6,800,000	(10,120,000)
Accounts payable	(685,000)	(72,000)	(265,000)
Accrued personnel-related expenses	(1,604,000)	(578,000)	227,000
Deferred revenue	(4,352,000)	(5,484,000)	(9,670,000)
Deferred rent			802,000
Other accrued liabilities, and other long-term liabilities	1,695,000	(5,699,000)	(3,854,000)
Operating lease liabilities	(4,340,000)	(2,905,000)
Net cash used in operating activities	(64,654,000)	(113,866,000)	(122,514,000)
Investing activities
Purchases of marketable securities	(286,326,000)	(193,063,000)	(377,365,000)
Maturities of marketable securities	169,016,000	321,015,000	386,200,000
Proceeds from sales of property and equipment	6,737,000
Purchases of property and equipment	(56,000)	(1,776,000)	(11,331,000)
Net cash (used in) provided by investing activities	(110,629,000)	126,176,000	(2,496,000)
Financing activities
Proceeds from follow-on public offering of common stock, net of issuance costs	163,214,000		107,612,000
Proceeds from issuance of common stock under equity incentive plans	4,180,000	1,136,000	3,963,000
Repurchase of shares to satisfy tax withholding obligations	(2,352,000)	(1,599,000)	(2,402,000)
Proceeds from disgorgement of stockholder's short-swing profits	16,727,000
Net cash provided by (used in) financing activities	188,905,000	(463,000)	109,173,000
Net increase (decrease) in cash and cash equivalents and restricted cash	13,622,000	11,847,000	(15,837,000)
Cash, cash equivalents and restricted cash at beginning of period	57,343,000	45,496,000	61,333,000
Cash, cash equivalents and restricted cash at end of period	70,965,000	57,343,000	45,496,000
Supplemental information
Property and equipment purchases included in accrued liabilities		29,000	716,000
Lease liability arising from obtaining right-of-use asset	2,162,000
Public offering issuance costs included in accrued liabilities	34,000
Cash and cash equivalents at beginning of period	55,800,000	43,953,000	59,790,000
Restricted cash at beginning of period	1,543,000	1,543,000	1,543,000
Cash, cash equivalents and restricted cash at beginning of period	57,343,000	45,496,000	61,333,000
Cash and cash equivalents at end of period	69,422,000	55,800,000	43,953,000
Restricted cash at end of period	1,543,000	1,543,000	1,543,000
Cash, cash equivalents and restricted cash at end of period	70,965,000	$ 57,343,000	$ 45,496,000
At-The-Market [Member]
Financing activities
Proceeds from follow-on public offering of common stock, net of issuance costs	$ 7,136,000

Business

Business	12 Months Ended
	Dec. 31, 2020
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. We have reclassified certain prior period amounts within our footnotes to conform to our current period presentation.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
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 U.S. generally accepted accounting principles , or GAAP Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable. 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 recorded at face value, or cost, which approximates 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 into in December 2016. The certificate of deposit has a term of one month. We are required to maintain this restricted cash balance, the amount of which is subject to reduction starting on January 1, 2023, if certain conditions are met, for the duration of this 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, which is part of other income, net. 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. 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 Measurements We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify assets as Level 3 within the valuation hierarchy. We had a non-recurring Level 3 fair value measurement as of December 31, 2020 related to our operating lease right-of-use asset and related leasehold improvements and furniture and fixtures as part of an impairment review in connection with our entry into a sublease agreement, or the facility sublease, with Sutro Biopharma, Inc., or Sutro, pursuant to which we sublet to Sutro office and laboratory space at our current facilities. See Note 5 for additional information regarding the facility sublease and asset group. The following tables summarize 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, 2020 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Money market funds $ 21,250 $ 21,250 $ — $ — U.S. Treasury securities 157,621 157,621 — — Agency bonds 14,991 14,991 — — Commercial paper 53,222 — 53,222 — Certificate of deposit 1,543 — 1,543 — Total $ 248,627 $ 193,862 $ 54,765 $ — December 31, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Money market funds $ 21,706 $ 21,706 $ — $ — U.S. Treasury securities 35,498 35,498 — — Agency bonds 48,834 48,834 — — Corporate bonds 1,800 — 1,800 — Commercial paper 19,195 — 19,195 — Certificate of deposit 1,543 — 1,543 — Total $ 128,576 $ 106,038 $ 22,538 $ — 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 are reviewed for impairment whenever events or changes in circumstances indicate that the assets may not be recoverable. Recoverability of these assets is measured by comparing their carrying amounts to the future undiscounted cash flows the assets are expected to generate. If an asset is impaired, the impairment to be recognized equals the amount by which the carrying value exceeds the asset’s fair value. The primary measure of fair value is discounted cash flows, which includes significant estimates primarily related to the discount rate and projected cash flows. The discount rate considers the relevant risk associated with asset-specific characteristics and the uncertainty related to the ability to achieve the projected cash flows. In connection with the corporate restructurings that we undertook in 2019: • We entered the facility sublease with Sutro in September 2020 in order to reduce our corporate facilities footprint. Accordingly, we evaluated our operating lease right-of-use asset and related leasehold improvements and furniture and fixtures and determined that the carrying value of this asset group was no longer recoverable. We calculated the fair value of this asset group using discounted cash flows, which have significant unobservable inputs related to discount rate (7%) and projected cash flows. We elected to exclude the operating lease obligation from the asset group when testing whether the carrying amount of the asset group was recoverable. As a result, we classified the fair value of this asset group within Level 3 of the fair value hierarchy. See Note 5 for additional information regarding the facility sublease and this asset group. • We evaluated our laboratory equipment and determined that the carrying value was no longer recoverable. See Note 14 for additional information regarding the laboratory equipment. Leases Effective January 1, 2019 , we adopted Financial Accounting Standards Board, or FASB, Accounting Standard Update, or ASU, No. 2016-02, Leases (Topic 842) , or Topic 842. We record a liability to make lease payments and a right-of-use asset for our right to use the underlying assets for the applicable lease terms on our balance sheet. We elected the “package of practical expedients,” which permitted us to not reassess our prior conclusion about lease identification, lease classification, and initial direct costs. We also elected (i) to account on the balance sheet with a lease term at the commencement date of twelve months or less. We determine if an arrangement is a lease at inception date. All our leases are classified as operating leases. Operating lease liabilities and the corresponding right-of-use assets are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. When available, we use the rate implicit in the lease to discount lease payments to present value. However, our leases do not provide a readily determinable implicit rate. Therefore, we must estimate our incremental borrowing rate to discount the lease payments based on information available at lease commencement. We include options to extend the lease in our lease liability and right-of-use asset when it is reasonably certain that we will exercise the option. Our lease agreements do not contain any material residual value guarantees or material restrictive covenants . We recognize operating lease cost as a single lease cost on a straight-line basis. However, once a right-of-use asset is impaired, lease cost for the arrangement that generated that right-of-use asset is no longer recognized on a straight-line basis due to variability in the interest amortization. Variable lease payments primarily include building operating expenses as charged to us by our landlords and are not included in the lease liability; rather, they are recognized on the statement of operations and comprehensive loss in the period in which the obligation is incurred. We recognize sublease income on a straight-line basis. Variable sublease payments are recognized when the corresponding variable lease payments of the underlying master lease are incurred. Sublease income, including the variable sublease payments, are recorded in other income, net on the statement of operations and comprehensive loss. Restructuring and Other Charges We account for costs related to our restructuring activities in accordance with ASC 420, Exit or Disposal Cost Obligations We will recognize other restructuring costs, including lease or other contract termination costs incurred in connection with terminating a contract before the end of its term, when we terminate the contract in accordance with its terms. See Note 14 for additional information regarding charges related to our corporate restructurings. Revenue Recognition Effective January 1, 2018, we adopted FASB ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) The terms of our license and collaborative research and development agreements include upfront and license fees, research, development and other funding or reimbursements, milestone and other contingent payments for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of commercialized products. Arrangements that include upfront payments may require deferral of revenue recognition to a future period until we perform obligations under these arrangements. We record research and development funding payable to us as accounts receivable when our right to consideration is unconditional. The event-based milestone and other contingent payments represent variable consideration, and we use the most likely amount method to estimate this variable consideration . Given the high degree of uncertainty around the occurrence of these events, we determine the milestone and other contingent amounts to be fully constrained until the uncertainty associated with these payments is resolved. We will recognize revenue from sales-based royalty payments when or as the sales occur. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. A performance obligation is a promise in a contract to transfer a distinct good or service and is the unit of accounting in Topic 606. A contract’s transaction price is allocated among each distinct performance obligation based on relative standalone selling price and recognized as revenue when, or as, the applicable performance obligation is satisfied. Under Topic 606, we elected to use the practical expedient permitted related to adoption, which does not require us to disclose certain information regarding our remaining performance obligations as of the end of the reporting period prior to the initial date of adoption. Additionally, we elected the practical expedient for certain research and development funding which allows us to recognize revenue in the amount for which we have a right to invoice if our right to consideration is an amount that corresponds directly to the value of our performance completed to date. As a result, we effectively bypass the steps of determining the transaction price and allocating that transaction price to the performance obligation . 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. 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 and contract research organizations, or CROs, and clinical manufacturing organizations, or CMOs, that conduct and manage preclinical studies and clinical trials on our behalf based on actual time and expenses incurred by such entities. Further, we accrue expenses related to clinical trials based on the level of patient activity according to the relevant 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. 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 awards, or RSAs, and stock option awards. We have granted RSAs, some of which are subject to performance conditions or market conditions. For RSAs with only service conditions, stock-based compensation cost is based on the closing market price of our common stock at the date of grant and is recognized as expense ratably over the requisite service period. For RSAs subject to performance conditions, stock-based compensation cost is calculated similarly and is recognized as expense using the accelerated attribution recognition method when it is probable that the performance condition will be achieved. For RSAs subject to market conditions, we base the fair value of the awards on a Monte Carlo simulation model and recognize stock-based compensation cost commencing at the grant date over the derived service period. Performance- and market-based awards require estimates as to the probability of certain outcomes—the probability of the achievement of performance conditions and the probability of various market-based outcomes, respectively—which require a high degree of judgment. For stock option awards, stock-based compensation cost is measured at the grant date, based on the fair value 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 account for forfeitures as they occur by reversing any expense recognized for unvested awards. Employee Benefit Plan We have a 401(k) Plan for all of our employees. Eligible employees may contribute through payroll deductions, and we may match the employees’ 401(k) contributions, at our discretion and not to exceed a prescribed annual limit per employee. Under this matching program, we contributed $0.3 million, $0.7 million and $1.0 million for the years ended December 31, 2020, 2019 and 2018, respectively. 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. Valuation allowances are provided when the expected realization of the deferred tax assets does not meet the more-likely-than-not criteria. This assessment requires a high degree of judgment. As a result, deferred tax assets at the end of 2020 and 2019 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. Accounting Pronouncements Recently Adopted Leases In February 2016, FASB issued Topic 842, which amended existing guidance to require substantially all leases to be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability, including leases currently accounted for as operating leases. We adopted Topic 842, effective January 1, 2019, using the updated modified retrospective transition method, in which the new standard is applied as of the date of initial adoption. We recognized and measured agreements executed prior to the date of initial adoption that were considered leases on January 1, 2019. No cumulative effect adjustment of initially applying the standard to the opening balance of retained earnings was made upon adoption. Upon adoption, we derecognized $19.8 million in deferred rent and ecognized $52.5 million in lease liabilities and $33.3 million in right-of-use assets on our balance sheet Revenue recognition In November 2018, FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808) clarifies when certain transactions between collaborative arrangement participants should be accounted for under Topic 606 and incorporates unit-of-account guidance consistent with Topic 606 to aid in this determination. We adopted ASU 2018-18, effective January 1, 2020, to be applied retrospectively to the date of initial application of Topic 606. The adoption of ASU 2018-18 had no effect on our financial statements and disclosures. In May 2014, FASB issued Topic 606, which superseded nearly all existing revenue recognition guidance under GAAP. We adopted Topic 606, effective January 1, 2018, using the modified retrospective transition method, in which the new standard is applied as of the date of initial adoption. We applied the standard to contracts that were not completed at the date of initial application. We recorded the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings. The adoption of Topic 606 resulted in a decrease of $1.4 million to deferred revenue and an increase of $1.4 million to retained earnings as of January 1, 2018. Our adoption of Topic 606 effective January 1, 2018 affected the following financial statement line items (in thousands, except per share data): Year Ended December 31, 2018 Condensed Statement of Operations and Comprehensive Loss Under Topic 606 Under Topic 605 Effect of change Collaboration and license revenue $ 49,868 $ 52,329 $ (2,461 ) Operating expenses 196,023 196,023 — Operating loss (146,155 ) (143,694 ) (2,461 ) Net loss (140,447 ) (137,986 ) (2,461 ) Net loss per share - basic and diluted (4.13 ) (4.06 ) (0.07 ) Year Ended December 31, 2018 Condensed Statement of Cash Flows Under Topic 606 Under Topic 605 Effect of change Net loss $ (140,447 ) $ (137,986 ) $ (2,461 ) Decrease in deferred revenue 1,373 — 1,373 Changes in operating assets and liabilities: Receivables from collaborative partner 8,037 8,037 — Deferred revenue (11,043 ) (12,131 ) 1,088 Cash, cash equivalents and restricted cash: At beginning of period 61,333 61,333 — At end of period 45,496 45,496 — Other In August 2018, FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework In June 2016, FASB issued ASU No. 2016-13, Financial Instruments–Credit Losses (Topic 326) In April 2015, FASB issued ASU No. 2018-15, Intangibles–Goodwill and Other–Internal-Use Software (Topic 350) Accounting Pronouncements Not Yet Adopted In December 2019, FASB issued ASU No. 2019-12, Income Taxes–Simplifying the Accounting for Income Taxes (Topic 740) We do not anticipate that the adoption of ASU 2019-12 will have a material effect on our financial statements.

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	12 Months Ended
	Dec. 31, 2020
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 (in thousands): December 31, 2020 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 21,250 $ — $ — $ 21,250 U.S. Treasury securities 157,642 3 (24 ) 157,621 Agency bonds 14,998 — (7 ) 14,991 Commercial paper 53,219 4 (1 ) 53,222 Total cash equivalents and marketable securities 247,109 7 (32 ) 247,084 Less: cash equivalents (29,247 ) — — (29,247 ) Total marketable securities $ 217,862 $ 7 $ (32 ) $ 217,837 December 31, 2019 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 21,706 $ — $ — $ 21,706 U.S. Treasury securities 35,471 27 — 35,498 Agency bonds 48,790 44 — 48,834 Corporate bonds 1,800 — — 1,800 Commercial paper 19,188 7 — 19,195 Total cash equivalents and marketable securities 126,955 78 — 127,033 Less: cash equivalents (26,453 ) — — (26,453 ) Total marketable securities $ 100,502 $ 78 $ — $ 100,580 As of December 31, 2020, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Debt securities maturing: In one year or less $ 185,783 $ 185,759 In one to two years 32,079 32,078 Total marketable securities $ 217,862 $ 217,837 The following table summarizes our marketable securities in a continuous unrealized loss position as of December 31, 2020 (in thousands): Amortized Unrealized Estimated Cost Basis Losses Fair Value Less than 12 months: U.S. Treasury securities $ 133,822 $ (24 ) $ 133,798 Agency bonds 14,998 (7 ) 14,991 Commercial paper 19,981 (1 ) 19,980 Total $ 168,801 $ (32 ) $ 168,769 As of December 31, 2020, a total of 14 individual U.S. Treasury securities, one agency bond and two commercial paper had been in an unrealized loss position for 12 months or less, and the losses were determined to be temporary in nature. There were no marketable securities in a continuous unrealized loss position for 12 months or less as of December 31, 2019. Our cash equivalents and marketable securities have an average maturity of approximately eight months and the longest maturity is 18 months. 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, 2020. It is not more likely than not that we will be required to sell the investments before recovery of their amortized cost bases. There were no sales of available-for-sale securities in any of the periods presented. As such, no allowance for credit losses was recognized. We also considered the current and expected future economic and market conditions surrounding the COVID-19 pandemic and determined that the estimate of credit losses was not significantly impacted.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and Equipment	4. Property and Equipment Property and equipment consist of the following (in thousands): December 31, 2020 2019 Computer equipment and software $ 1,981 $ 2,281 Furniture and fixtures 842 968 Laboratory equipment 913 4,219 Leasehold improvements 17,265 22,175 21,001 29,643 Less: accumulated depreciation and amortization (9,792 ) (7,109 ) Property and equipment, net $ 11,209 $ 22,534 We recognized fixed asset impairments during the years ended December 31, 2020 and 2019 as a result of the corporate restructuring activities that commenced in 2019. See Notes 5 and 14 for additional information on these impairments.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	5. Leases In December 2016, we entered into a lease agreement, which we refer to as the corporate facility lease, for our corporate office and laboratory facility at 111 Oyster Point Boulevard, South San Francisco, California In October 2020, we entered into an agreement to rent laboratory space, which we refer to as the laboratory facility lease. We occupied this space beginning in December 2020. The laboratory facility lease commenced on November 1, 2020 and had an initial term of two months and renews automatically for subsequent two-month In July 2018, we entered into a lease agreement for the installation, operational qualifications and performance qualifications of four sequencing instruments to support our bemarituzumab program, which we refer to as the instruments lease. We terminated the instruments lease in May 2020 The termination of the instruments lease was accounted for by derecognizing the lease assets from the balance sheet in the second quarter of 2020. The lease liabilities were derecognized from the balance sheet as the liabilities were extinguished when the final lease payment was made. Sublease In October 2019, we commenced a corporate restructuring to extend our cash runway and ensure long-term sustainability. As part of the restructuring, in order to reduce our corporate facilities footprint, in September 2020, we entered into a sublease agreement with Sutro, or the facility sublease, pursuant to which we agreed to sublet to Sutro the approximately 115,466 rentable square feet at the premises. The facility sublease is subordinate to the corporate facility lease. The facility sublease has a total term of approximately 6.5 years, beginning on the rent commencement date, with no option to extend the facility sublease. The term of the facility sublease concludes at the same time as the underlying corporate facility lease. We determined that the facility sublease is an operating lease, which is consistent with the classification of the underlying corporate facility lease. Under the facility sublease, we are subletting three of the four floors of the premises, or the initial premises, with Sutro’s obligation to pay rent for the initial premises beginning on the rent commencement date of July 2, 2021, or the initial premises commencement date. The initial premises commencement date was determined as nine months after October 2, 2020, which was the date of the written consent of the landlord of the underlying corporate facility lease. We will sublet the fourth floor, or the expansion premises, on the date that is 24 months following the initial premises commencement date, or sooner if Sutro provides six months’ prior written notice, or the expansion premises commencement date. Sutro’s obligation to pay rent for the expansion premises will commence on the expansion premises commencement date. The facility sublease contains scheduled rent increases over the sublease term. With the execution of the facility sublease, in which the lease cost for the term of the facility sublease exceeds the anticipated sublease income for that same period, we tested the operating lease right-of-use assets and related leasehold improvements and furniture and fixtures for impairment as of September 1, 2020 . We recorded an impairment loss of $13.8 million on the operating lease right-of-use asset and related leasehold improvements and furniture and fixtures as they relate to the initial premises, of which we recorded $7.3 million in our research and development costs and $6.5 million in our general and administrative costs within our statement of operations and comprehensive loss. The impairment loss adjusted the carrying values of the operating lease right-of-use assets to $20.1 million, the leasehold improvements to $11.2 million, and the furniture and fixtures to $0.3 million. We continue to amortize the operating lease right-of-use asset, at its revised carrying value, to operating lease cost, but now on a straight-line basis. Lease Cost, Income and Related Supplemental Information The tables below present lease cost, income and related supplemental information (in thousands, except as otherwise indicated): Year Ended December 31, 2020 2019 Lease cost (as lessee): Operating lease cost $ 6,614 $ 6,140 Variable lease cost 2,418 1,762 Total lease cost $ 9,032 $ 7,902 Lease income (as lessor): Operating sublease income $ 1,146 $ — Supplemental cash flow information (as lessee): Cash paid for amounts included in the measurement of operating lease liabilities $ 7,855 $ 6,693 December 31, 2020 2019 Supplemental balance sheet information (as lessee): Weighted-average remaining lease term (in years) 6.8 8.0 Weighted-average discount rate (%) 7.33 % 7.44 % Rent expense for the year ended December 31, 2018 was $5.9 million. Minimum Lease Payments The table below presents the undiscounted cash flows for each of the next five years and the total of the remaining years. For the facility leases, the undiscounted cash flows are reconciled to the operating lease liabilities recorded on the balance sheet, as follows (in thousands): Facility Leases (1) Facility Sublease 2021 $ 8,389 $ 2,547 2022 8,652 — 2023 8,569 6,310 2024 8,341 7,476 2025 8,632 7,737 2026 and beyond 18,194 16,297 Total minimum lease payments 60,777 $ 40,367 Less: amount of lease payments representing interest (13,343 ) Present value of future minimum lease payments 47,434 Less: operating lease obligations, current portion (5,125 ) Operating lease obligations, long-term portion $ 42,309 (1) The minimum lease payments for the facility sublease assume that the expansion premises commencement date will be 24 months following the initial premises commencement date. These amounts will be adjusted if the actual timing differs from this assumption.

Other Accrued Liabilities

Other Accrued Liabilities	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Other Accrued Liabilities	6. Other Accrued Liabilities Other accrued liabilities consist of the following (in thousands): December 31, 2020 2019 Clinical development $ 6,521 $ 7,787 Manufacturing 2,193 540 Accrued trade payable 2,341 1,087 Other 330 245 Total accrued liabilities $ 11,385 $ 9,659

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stockholders' Equity	7. Stockholders’ Equity We have 110,000,000 shares of authorized capital stock issuable in series, all with a par value of $0.001 per share, of which 100,000,000 shares are designated as common stock and 10,000,000 shares are designated as preferred stock. Our Board of Directors, or our Board, is authorized to determine the designation, powers, preferences and rights of any such series. In November 2020, we closed on a public offering of 8,280,000 shares of our common stock, which included 1,080,000 shares sold upon the underwriters’ full exercise of their option to purchase additional shares, resulting in aggregate gross proceeds of $163.4 million, before deducting underwriting discounts and commissions and offering expenses payable by us, and net proceeds of approximately $163.2 million after deducting these amounts. In November 2020, we received $16.7 million related to the recovery of short-swing profits from one of our beneficial owners, a related party, under Section 16(b) of the Securities Exchange Act of 1934, as amended. We recognized these proceeds as a capital contribution from stockholders with an increase to additional paid-in capital on our balance sheet and as cash provided by financing activities on our statement of cash flows. In August 2020, we entered into a sales agreement with Cowen and Company, LLC, or Cowen, acting as sales agent, pursuant to which we may offer and sell, from time to time through Cowen, shares of our common stock having an aggregate offering price of up to $75.0 million in a series of one or more at-the-market equity offerings , or collectively, the ATM program . During 2020, we raised approximately $7.1 million in net proceeds under the ATM program . In January 2018, we closed on a public offering of 5,897,435 shares of our common stock, which included 769,230 shares sold upon the underwriters’ full exercise of their option to purchase additional shares, resulting in aggregate gross proceeds of $115.0 million, before deducting underwriting discounts and commissions and offering expenses payable by us, and net proceeds of approximately $107.6 million after deducting these amounts. Equity Incentive Plans In September 2013, our stockholders approved the 2013 Omnibus Incentive Plan, or the 2013 Plan. Any shares of common stock covered by awards granted under our 2002 Equity Incentive Plan or our 2010 Equity Incentive Plan, or collectively, 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 outstanding shares of common stock as of December 31 of the immediately preceding year. Under the 2013 Plan, any shares that are forfeited or expired are added back to the shares available for issuance. As of December 31, 2020, 2,657,782 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. 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 initial public offering, our Board determined the estimated fair value of our common stock. For all stock options granted after the completion of our initial public offering 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. The following table summarizes option activity and related information under the 2013 Plan and the Prior Plans: 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, 2020 3,314,722 $ 20.50 Options granted 2,000,502 $ 4.37 Options exercised (465,024 ) $ 8.43 Options forfeited (218,564 ) $ 9.65 Options expired (432,309 ) $ 34.30 Balance at December 31, 2020 4,199,327 $ 13.30 7.5 $ 33,125 Exercisable at December 31, 2020 2,298,658 $ 19.38 6.3 $ 11,787 The weighted-average grant-date fair value per share of stock options granted during the years ended December 31, 2020, 2019 and 2018 was $2.70, $4.96 and $10.85 per share, respectively. The total intrinsic value of stock options exercised during the years ended December 31, 2020, 2019 and 2018 was $4.0 million, $0.1 million and $2.4 million, respectively. We recorded stock-based compensation expense related to stock options of approximately $7.2 million, $14.3 million and $17.3 million for the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020, there was $6.2 million of total unrecognized compensation expense that we expect to recognize over a weighted-average period of 2.7 years. We have granted RSAs, which are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting and are not forfeitable once fully vested. The following table summarizes RSA activity and related information under the 2013 Plan: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at January 1, 2020 1,060,577 $ 11.24 RSAs granted 614,950 $ 4.91 RSAs vested (678,076 ) $ 11.06 RSAs forfeited (228,162 ) $ 10.84 Unvested balance at December 31, 2020 769,289 $ 6.46 The total fair value on the date of vesting of RSAs that vested in 2020, 2019 and 2018 was $5.2 million, $3.7 million and $6.2 million, respectively. We recorded stock-based compensation expense related to RSAs of approximately $2.8 million, $8.2 million and $11.6 million for the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020, there was $2.2 million of unrecognized compensation cost related to unvested employee RSAs that we expect to recognize over a weighted-average period of 2.3 years. Employee Stock Purchase Plan 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, 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 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, 2020, 1,227,894 shares of common stock were available for issuance under the ESPP. In November 2019, the compensation and management development committee of our Board provided that the number of shares of common stock available for issuance under the ESPP would not automatically increase on January 1, 2020 and as such, no new shares of common stock became available for issuance under the ESPP on January 1, 2020. Under the 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 79,828 shares under the ESPP in 2020. The compensation expense related to the ESPP was $0.2 million, $0.3 million and $0.5 million for the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020, there was $0.2 million of unrecognized compensation cost related to the ESPP, which we expect to recognize over 4.4 months. Stock-Based Compensation Total stock-based compensation expense recognized was as follows (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 3,279 $ 8,041 $ 15,426 General and administrative 6,908 14,774 14,042 Total $ 10,187 $ 22,815 $ 29,468 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, 2020 2019 2018 2020 2019 2018 Expected term (years) 5.0-6.3 5.0-6.3 5.5-6.3 0.5 0.5 0.5 Expected volatility 69-73% 67-68% 68-70% 107-199% 64-67% 47-94% Risk-free interest rate 0.4-1.3% 1.6-2.5% 2.6-2.9% 0.1-0.2% 1.6-2.4% 1.4-2.5% 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 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. Stock Option Exchange Program On July 1, 2019, we commenced a tender offer to our employees, excluding named executive officers, to exchange eligible stock options for replacement stock options with modified terms, or our exchange offer. Pursuant to the exchange offer, we offered these employees who held outstanding stock options granted on or before June 6, 2018 with an exercise price equal to or greater than $18.00 per share, or eligible options, the opportunity to tender each eligible option in exchange for a new stock option with modified terms, or new options. The exchange offer expired at 6:00 p.m., Pacific time, on July 29, 2019. As of the expiration of the exchange offer, there were 510,932 shares of our common stock underlying the eligible options. Pursuant to the exchange offer, 55 employees elected to exchange outstanding stock options, and we accepted for cancellation stock options to purchase an aggregate of 436,648 shares of common stock, representing approximately 85% of the total shares of common stock underlying the eligible options. On July 29, 2019, immediately following the expiration of the exchange offer, we granted new options to purchase 235,419 shares of common stock, each with an exercise price of $5.06 per share, which was the closing price per share of our common stock on Nasdaq on the grant date. As a result, 201,229 shares of common stock returned to the 2013 Plan reserve and became available for future issuance. Each new option vests in equal monthly amounts over either one or three years, depending on whether the tendered eligible option was fully vested as of July 29, 2019, has a maximum term of seven years and was granted as a nonqualified stock option under the 2013 Plan. The exchange of stock options was treated as a modification for accounting purposes. The incremental expense on the new options was fully recognized as of July 29, 2020 using the Black-Scholes option-pricing model over the new service period that began on the modification date of July 29, 2019. We are recognizing the unamortized expense remaining on the tendered options of $0.2 million as of December 31, 2020 over the remainder of the original requisite service period.

Earnings per Share

Earnings per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Earnings per Share	8. Earnings per Share We compute basic per share amounts by dividing net loss by the weighted-average number of common shares outstanding during the period. Diluted per share amounts are based on the weighted-average number of common shares outstanding and dilutive potential common shares, which include shares that may be issued under our equity incentive plans and determined using the treasury stock method, during the period. For the years ended December 31, 2020, 2019 and 2018, d We excluded the following securities from the calculation of diluted per share amounts as the effect would have been antidilutive (in thousands): Year Ended December 31, 2020 2019 2018 Options to purchase common stock 4,633 3,760 3,710 RSAs 1,109 1,273 880 Total 5,742 5,033 4,590

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
License and Collaboration Agreements	9. License and Collaboration Agreements The following tables present changes in the balances of our contract assets, including receivables from collaboration partners, and contract liabilities, including deferred revenue (in thousands): Contract Assets Balance at January 1, 2020 $ 4,097 Additions 4,023 Deductions (8,035 ) Balance at December 31, 2020 $ 85 Contract Liabilities Balance at January 1, 2020 $ 6,409 Additions for advance billings 1,190 Deductions for performance obligations satisfied: In current period (4,516 ) In prior periods related to measure of progress updates (1,026 ) Balance at December 31, 2020 $ 2,057 The following table presents license and collaboration revenue by collaboration partner or licensee (in thousands): Year Ended December 31, 2020 2019 2018 Milestone payments: (1) Cabiralizumab Collaboration - BMS $ — $ — $ 25,000 Other payments: China Collaboration - Zai Lab 5,455 4,385 5,068 Cabiralizumab Collaboration - BMS 2,649 9,060 13,441 Immuno-oncology Research Collaboration - BMS — 1,429 6,086 License Agreement - Seagen 5,074 — — Other — — 273 Total $ 13,178 $ 14,874 $ 49,868 (1) The agreements with each collaboration partner and licensee are discussed in more detail in the following sections. These agreements generally may be terminated due to material and uncured breaches, insolvency of either party, unilateral decision by the collaboration partner or licensee upon prior written notice, expiration of royalty or payment obligations, or challenges to patents which are relevant to the related agreement. Under the agreement with Zai Lab (Shanghai) Co., Ltd., we may terminate the agreement in its entirety with written notice for Zai Lab’s material breach of its diligence obligations with respect to development and obtaining marketing approval, and may terminate the agreement on a region-by-region basis for Zai Lab’s breach of its diligence obligations with respect to timely commercialization of a licensed product in a region following marketing approval. In addition to the agreements discussed in the following sections, we also have agreements in which we have no remaining performance obligations, but for which we may receive milestone and royalty payments from the collaboration partner or licensee. Bristol-Myers Squibb Company Immuno-Oncology Research Collaboration In March 2014, we entered into a research collaboration and license agreement, or the immuno-oncology research collaboration, with Bristol-Myers Squibb Company, or BMS, 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 research collaboration, we granted to BMS an exclusive, worldwide license to research, develop and commercialize products directed towards certain targets in the checkpoint pathways. BMS has an option to take exclusive licenses to additional targets we may identify in these checkpoint pathways pursuant to the research plan under the immuno-oncology research collaboration. Based on data arising from our activities under the research plan, 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 immune checkpoint pathways. We received an upfront non-refundable payment of $20.0 million from BMS in connection with the execution of the immuno-oncology research collaboration. BMS also paid us $13.7 million in research funding from 2014 through 2019, during which we performed certain research activities. In connection with entering into the immuno-oncology research collaboration, BMS purchased 994,352 shares of our common stock at a price per share that exceeded the fair value of our common stock by a total of $2.4 million. We are eligible to receive certain developmental-, regulatory- and sales-based 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. We identified one performance obligation for the research license to access our technology, the exclusive commercial license and research activities. BMS’s option to select additional collaboration targets is not priced at a discount and therefore does not represent one or more performance obligations for which the transaction price would be allocated. The transaction price of $36.1 million includes the $20.0 million upfront fee, $13.7 million of research funding and $2.4 million of equity premium. We concluded that the transaction price should not include the variable consideration related to maintenance fees and unachieved developmental and regulatory milestones as this consideration was considered to be constrained as it is probable that the inclusion of such variable consideration could result in a significant reversal in revenue in the future. Any milestone payments triggered during the periods presented are included in the table at the start of this note. We will recognize any consideration related to sales-based payments (including milestones and royalties) when the related sales occur, as we have determined that these amounts relate predominantly to the license granted and therefore will be recognized on the later to occur of satisfaction of the performance obligation or the occurrence of the related sales. We will re-evaluate the transaction price at each reporting period as uncertain events are resolved and other changes in circumstances occur. For the year ended December 31, 2020, no adjustments were made to the transaction price. Under the input method, we recognize revenue on the basis of our efforts or inputs applicable to the satisfaction of a performance obligation (e.g., resources consumed, labor hours expended, costs incurred, or time elapsed) relative to the total expected inputs applicable to the satisfaction of that performance obligation. We concluded that we will recognize revenue based on actual costs incurred as a percentage of total budgeted costs as we complete our performance obligation. As the performance obligation was fully satisfied through March 31, 2019, the transaction price of $36.1 million was fully recognized as collaboration revenue. Revenue recognized from the performance obligations was $0 million, $1.4 million and $6.1 million for the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020 and 2019, we had no deferred revenue relating to the immuno-oncology research collaboration. License and Collaboration Agreement In October 2015, we entered into a license and collaboration agreement, or the cabiralizumab collaboration agreement, 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. BMS is responsible for manufacturing and commercializing each licensed product and we retain rights to a U.S. co-promotion option. The cabiralizumab collaboration agreement supersedes the clinical trial collaboration agreement we entered into with BMS in November 2014, or the original collaboration agreement. We assessed the two agreements separately as standalone agreements. In February 2020, BMS informed us that its randomized, controlled multi-arm Phase 2 clinical trial testing cabiralizumab in combination with Opdivo We received an upfront non-refundable payment of $30.0 million from BMS in connection with the execution of the original collaboration agreement. We completed enrollment and treatment of patients in our Phase 1a/1b clinical trial to evaluate the safety, tolerability and preliminary efficacy of combining Opdivo Under the original collaboration agreement, we identified one performance obligation for the execution of a Phase 1a/1b clinical trial of cabiralizumab in combination with Opdivo We used the input method to measure progress toward completion of the performance obligation and concluded that we will recognize revenue based on actual costs incurred by our CRO as a percentage of total budgeted costs as we complete our performance obligation. We will recognize revenue from reimbursements when we have the right to invoice BMS. As the performance obligation was fully satisfied through June 30, 2020, the transaction price of $30.0 million was fully recognized as collaboration revenue. We recognized $0.8 million, $4.4 million and $6.6 million of the transaction price as revenue for the years ended December 31, 2020, 2019 and 2018, respectively. Revenue recognized for reimbursements was $1.8 million, $4.7 million and $6.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. Under the cabiralizumab collaboration agreement, we identified the following performance obligations: (1) license grant to BMS and (2) transfer of licensed know-how to BMS. The transaction price consisted of a $350.0 million non-refundable up-front fee. As the performance obligations were fully satisfied in 2015, the transaction price of $350.0 million was fully recognized as revenue concurrent with the transfer of the license and know-how in 2015. We concluded that the transaction price should not yet include milestone payments that may become due as they are fully constrained. Any milestone payments triggered during the periods presented are included in the table at the start of this note. We will recognize any consideration related to royalties when the related sales occur, as we have determined that these amounts relate predominantly to the license granted and therefore will be recognized upon the occurrence of the related sales. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the year ended December 31, 2020, no adjustments were made to the transaction price. As of December 31, 2020 and 2019, we had deferred revenue relating to the license and collaboration agreements of $0 million and $0.8 million, respectively. Zai Lab China License and Collaboration Agreement In December 2017, we entered into a license and collaboration agreement, or the China collaboration agreement, with Zai Lab, pursuant to which we granted Zai Lab an exclusive license to develop and commercialize bemarituzumab, and all fragments, conjugates, derivatives and modifications thereof, or the licensed antibody, in China, Hong Kong, Macau and Taiwan, each a region and collectively, the territory. Zai Lab will be responsible, at its expense, for (i) developing and commercializing products containing the licensed antibody, each, a licensed product, under a territory development plan and (ii) performing certain development activities to support our global development and registration of licensed products, including our Phase 3 FIGHT trial, in the territory under a global development plan. We received an upfront non-refundable and non-creditable payment of $5.0 million ($4.2 million after netting of value-added tax withholdings) from Zai Lab in connection with the execution of the China collaboration agreement. With respect to each licensed product, we are eligible to receive developmental and regulatory milestone payments. Zai Lab will also be obligated to pay us a royalty, on a licensed product-by-licensed product and region-by-region basis. In addition, Zai Lab agreed to reimburse us for certain global development activities, which is limited to a maximum of $10.0 million, and certain costs for the development of companion diagnostics. We identified the following performance obligations: (1) license grant to Zai Lab together with the transfer of licensed know-how, development drug supply and global development activities, or the license grant, and (2) development of companion diagnostics. Zai Lab has the option to purchase commercial drug supply from us pursuant to a separate commercial supply agreement to be negotiated in the future. The commercial drug supply will be accounted for as a separate contract when Zai Lab exercises this option. As of December 31, 2020, the transaction price of $9.6 million consists of the $4.2 million upfront fee, $3.7 million of expected reimbursement from Zai Lab for global development activities and a $1.7 million clinical development milestone payment. We have not included the remaining regulatory milestone payments in the transaction price as all such milestone amounts are fully constrained. Any milestone payments triggered during the periods presented are included in the table at the start of this note. We will recognize any consideration related to royalties when the related sales occur, as we determined that these amounts relate predominantly to the license granted and therefore will be recognized upon the occurrence of the related sales. We concluded that the reimbursement of costs incurred for the development of companion diagnostics qualifies for the practical expedient under Topic 606, which allows us to recognize revenue in the amount for which we have a right to invoice if our right to consideration is an amount that corresponds directly to the value to Zai Lab of our performance completed to date. We therefore effectively bypass the steps of determining the transaction price and allocating that transaction price to the performance obligation. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the year ended December 31, 2020, the transaction price decreased to $9.6 million (from $14.7 million), primarily as a result of our decision to amend the FIGHT trial from a Phase 3 design to a randomized Phase 2 trial. We use the input method to measure progress toward completion of the performance obligation for the license grant. We concluded that revenue will be recognized based on actual costs incurred by our CRO as a percentage of total budgeted costs as we complete our performance obligation. For the year ended December 31, 2020, the total budgeted costs used in our measure of progress decreased as a result of our decision to amend the FIGHT trial from a Phase 3 design to a randomized Phase 2 trial. The decrease in total budgeted costs resulted in further progress made towards satisfying our performance obligation for the license grant and a cumulative catch-up adjustment to revenue . There was a deduction to our contract liabilities as of December 31, 2020 for performance obligations satisfied during the year ended December 31, 2020 and for performance obligations satisfied in prior periods related to measure of progress update. Revenue recognized for the license grant performance obligation was $3.6 million, $1.4 million and $1.7 million for the years ended December 31, 2020, 2019 and 2018, respectively. Revenue recognized for the companion diagnostics development performance obligation was $1.9 million, $3.0 million and $3.3 million for the years ended December 31, 2020, 2019 and 2018, respectively. Of the remaining transaction price of $2.9 million, we recorded $2.1 million in deferred revenue, which we will recognize over the estimated performance period for satisfaction of the performance obligations. The remaining $0.8 million of the transaction price will be recorded in deferred revenue when invoiced as we complete global development activities. As of December 31, 2020 and 2019, we had deferred revenue relating to the China collaboration agreement of $2.1 million and $5.1 million, respectively. Seagen License Agreement In February 2020, we entered into a license agreement, or the Seagen license agreement, with Seagen Inc., or Seagen, pursuant to which we granted Seagen an exclusive worldwide license to a family of monoclonal antibodies that are directed to a single target and Seagen is responsible for research, development, manufacturing and commercialization of novel antibody-drug conjugate products based on these antibodies. We received an upfront non-refundable payment of $5.0 million from Seagen in connection with the execution of the Seagen license agreement. We are eligible to receive up to (i) $132.0 million in specified developmental and regulatory milestone payments for the first achievement of such milestone events by the first licensed product, (ii) $68.0 million in specified developmental and regulatory milestone payments for the first achievement of such milestone events by the second licensed product, and (iii) $19.0 million in specified developmental and regulatory milestone payments for each achievement of such milestone events by a subsequent licensed product. We are also eligible to receive up to $162.5 million in sales-based contingent payments per licensed product. Seagen will also be obligated pay us a mid-single-digit percentage royalty on net sales of each licensed product in a region until the latest of: (i) 11 years after the first commercial sale of such licensed product in such region; (ii) the expiration of certain patents covering such licensed product in such region; and (iii) the date on which any applicable regulatory exclusivities with respect to such licensed product expire in such region. We are also eligible to receive annual maintenance fees of $0.2 million and reimbursement for consulting support and certain prosecution and maintenance costs for our patents. We identified one performance obligation for the license grant. The transaction price consists of the $5.0 million upfront fee. As the performance obligation was fully satisfied as of March 31, 2020, the transaction price of $5.0 million was fully recognized. We concluded that the transaction price should not include the variable consideration related to maintenance fees and unachieved developmental and regulatory milestones as this consideration was considered to be constrained as it is probable that the inclusion of such variable consideration could result in a significant reversal in revenue in the future. Any milestone payments triggered during the periods presented are included in the table at the start of this note. We will recognize any consideration related to sales-based payments when the related sales occur, as we have determined that these amounts relate predominantly to the license granted and therefore will be recognized on the later to occur of satisfaction of the performance obligation or the occurrence of the related sales. We will recognize revenue from reimbursements when we have the right to invoice Seagen. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the year ended December 31, 2020, we recognized revenue of $0.1 million for reimbursements.

Acquired Technologies

Acquired Technologies	12 Months Ended
	Dec. 31, 2020
Research And Development [Abstract]
Acquired Technologies	10. Acquired Technologies The following agreements will remain in effect until the expiration of our royalty obligations under each agreement, unless earlier terminated. For each licensed product under each agreement, we are obligated to pay royalties on net sales of such licensed product on a country-by-country basis for the longer of the life of the licensed patents covering such licensed product in such country or 10 years after the first commercial sale of such licensed product in such country. Galaxy Biotech, LLC In December 2011, we entered into a license agreement with Galaxy Biotech, LLC, or Galaxy, pursuant to which Galaxy granted us an exclusive worldwide license to develop and commercialize FGFR2b antibodies, including bemarituzumab. Under the license agreement, we are obligated to use commercially reasonable efforts to develop and commercialize at least one licensed product in at least one tumor indication. We are required to make payments based upon the achievement of certain intellectual property, development, regulatory, and commercial milestones, as well as royalties on future net sales of licensed products, 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 Phase 1 clinical trial of bemarituzumab, which milestones were deemed achieved as of December 31, 2016. In May 2017, we further amended the license agreement to align the net sales definition under the agreement to the net sales definition under any sublicense we may grant under the agreement and to amend the termination provisions to allow for a direct license between Galaxy and any sublicensee upon termination of the agreement. We are obligated to pay Galaxy for intellectual property, development, regulatory and commercialization milestones of up to $77.4 million. We are also obligated to pay Galaxy tiered royalties on net sales of licensed products from high-single digit to low-double digit percentages. We made milestone payments to Galaxy of $0 million, $0 million and $9.5 million in 2020, 2019 and 2018, respectively. BioWa, Inc. and Lonza Sales AG In February 2012, we entered into a license agreement with BioWa, Inc. and Lonza Sales AG, or BioWa-Lonza, pursuant to which BioWa-Lonza granted us a non-exclusive license to use their Potelligent ® Under this agreement, we are obligated to pay BioWa-Lonza for development, regulatory and commercialization milestones achieved of up to $24.7 million and tiered royalties on net sales up to mid-single digit percentages. Under this agreement, we made milestone payments to BioWa-Lonza of $0 million, $0 million and $0.9 million in 2020, 2019 and 2018, respectively.

Other Income, Net

Other Income, Net	12 Months Ended
	Dec. 31, 2020
Other Income And Expenses [Abstract]
Other Income, Net	11. Other Income, Net The components of our other income, net were as follows (in thousands): Year Ended December 31, 2020 2019 2018 Interest income (see Note 3) $ 820 $ 4,740 $ 5,792 Sublease income (see Note 5) 1,146 — — Other (54 ) (4 ) (84 ) Total $ 1,912 $ 4,736 $ 5,708

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes The components of our income tax expense (benefit) were as follows (in thousands): Year Ended December 31, 2020 2019 2018 Current tax benefit Federal $ (6,630 ) $ — $ — State — — — Total current tax benefit (6,630 ) — — Deferred tax expense Federal — — — State — — — Total deferred tax expense — — — Total tax benefit $ (6,630 ) $ — $ — We recorded an income tax benefit for the year ended December 31, 2020 for a tax refund of minimum tax paid for 2015. The refund was available to us after we carried back our 2017 net operating losses. Under the CARES Act and after the carryback claim of net operating losses, we were able to request the refund of the 2015 alternative minimum tax upon the filing of our 2019 income tax return. The income tax expense (benefit) differs from the amount computed by applying the statutory federal income tax rate as follows (in thousands): Year Ended December 31, 2020 2019 2018 Federal statutory income tax $ (19,102 ) $ (28,812 ) $ (29,495 ) State statutory income tax 1 1 1 Stock compensation 1,966 4,055 3,698 Nontaxable equity premiums — (20 ) (85 ) Change in valuation allowance 17,754 32,540 38,953 Income from shareholder 3,513 — — Research and orphan drug credits (4,701 ) (8,015 ) (13,192 ) Tax benefit from alternative minimum tax credit refund (6,630 ) — — Other permanent items 569 251 120 Income tax benefit $ (6,630 ) $ — $ — The tax effects of temporary differences and carryforwards that give rise to significant portions of deferred tax assets and liabilities consist of the following (in thousands): December 31, 2020 2019 Net operating loss carryforwards $ 94,763 $ 85,928 Research and orphan drug credits 73,608 68,053 Deferred revenue 122 1,372 Stock-based compensation 5,390 7,562 Capitalized license and depreciation basis differences 2,906 3,196 Reserves, accruals and tenant improvement allowances 1,090 1,389 Operating lease liability 10,158 10,619 Total deferred tax assets 188,037 178,119 Less: valuation allowance (182,319 ) (168,691 ) Net deferred tax assets 5,718 9,428 Capitalized license and depreciation basis differences (808 ) (2,374 ) Operating right-of-use asset (4,557 ) (6,621 ) Prepaid expenses (353 ) (433 ) Total deferred tax liabilities (5,718 ) (9,428 ) Total net deferred tax assets $ — $ — Based on all available objective evidence, we determined it is more likely than not that we will not fully realize all our net deferred tax assets. 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 our net deferred tax assets for the years ended December 31, 2020 and 2019. We will continue to maintain a full valuation allowance on our 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 $13.6 million and $34.2 million during 2020 and 2019, respectively. As of December 31, 2020, our total net deferred tax assets, net of gross deferred tax liabilities, were $182.3 million. Due to our lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. In assessing the realizability of deferred tax assets, we considered whether it is more-likely-than-not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which the temporary differences representing net future deductible amounts become deductible. Due to our history of losses and lack of other positive evidence, we determined that it is more likely than not that our net deferred tax assets will not be realized, and therefore, the net deferred tax assets are fully offset by a valuation allowance. The deferred tax assets were primarily comprised of federal and state tax net operating losses and tax credit carryforwards. As of December 31, 2020, we had federal net operating loss carryforwards of approximately $416.3 million, which will start to expire beginning in 2024, and state net operating loss carryforwards of approximately $165.9 million, which will start to expire beginning in 2028. In addition, as of December 31, 2020, we had federal research and development and orphan drug credit carryforwards of approximately $67.2 million, which will start to expire in 2026, and state research and development credit carryforwards of approximately $24.8 million, which can be carried forward indefinitely. Utilization of the net operating loss carryforwards and credits may be subject to a substantial annual limitation due to the ownership change limitations provided by Section 382 and Section 383 of the Internal Revenue Code of 1986, as amended, and by similar state provisions. The annual limitation may result in the expiration of net operating losses and credits before utilization. Under the Tax Act, the carry forward period of net operating losses generated from 2018 forward is indefinite. However, the carryforward period for net operating losses generated prior to 2018 remains the same. To date, we have reduced our tax attributes (NOLs and tax credits) by approximately $1.4 million as a result of ownership changes. Any additional ownership change, if identified, may further limit the available tax attributes to offset our future taxable income in future periods. Unrecognized tax benefits are primarily tax credits for all years and state net operating loss carryover related for certain prior years. For the years ended December 31, 2020, 2019 and 2018, we recorded no interest or penalties related to income taxes. A reconciliation of our unrecognized tax benefits is as follows (in thousands): Year Ended December 31, 2020 2019 2018 Balance at beginning of year $ 18,393 $ 16,660 $ 13,584 Additions for prior year tax positions — 11 622 Additions for current year tax positions 1,020 1,722 2,454 Balance at end of year $ 19,413 $ 18,393 $ 16,660 In the event we are able to recognize these uncertain positions, most of the unrecognized tax benefits would reduce our effective tax rate. 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. We do not believe it is reasonably possible that our unrecognized tax benefits will significantly change within the next twelve months. We file U.S. and state income tax returns with varying statutes of limitations. The tax years from 2003 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, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies 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, which 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.

Restructuring and Other Charges

Restructuring and Other Charges	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Restructuring and Other Charges	14. Restructuring and Other Charges In January 2019, we implemented a corporate restructuring, or the January 2019 restructuring, to focus our resources on clinical development and late-stage research programs. Pursuant to the January 2019 restructuring, we eliminated 41 employee positions, representing approximately 20% of our then-current headcount, primarily in areas relating to research, pathology and manufacturing. The January 2019 restructuring was completed during the first quarter of 2019 , and restructuring charges to-date amounted to approximately $1.9 million for employee-related costs. In October 2019, we announced a second corporate restructuring, or the October 2019 restructuring, to extend our cash runway and ensure long-term sustainability. As part of the October 2019 restructuring, we reduced our workforce by 63 positions across all functions. The October 2019 restructuring was completed during the fourth quarter of 2020, and restructuring charges to-date amounted to approximately $5.3 million for employee-related costs. In conjunction with our 2019 corporate restructurings, we evaluated the laboratory equipment that we owned and determined that the carrying value was no longer recoverable and its estimated fair value was $3.9 million. An impairment loss of $1.9 million was recorded in research and development expense within our statement of operations and comprehensive loss, primarily during the fourth quarter of 2019. We reclassified the laboratory equipment from property and equipment to assets held for sale within our balance sheet for the first quarter of 2020. In April 2020, we sold the majority of the laboratory equipment through an auction conducted by a third-party vendor. We recorded a gain of $3.4 million for the proceeds of such auction against research and development expense within our statement of operations and comprehensive loss, all during the second quarter of 2020. The following table summarizes management’s estimates of costs that were expected to be incurred and were probable as of December 31, 2020 and the actual costs incurred to date through December 31, 2020 (in thousands): Total Estimated Restructuring Costs Total Restructuring Costs Incurred to Date Employee retention, severance and termination benefits (employee-related) $ 7,172 $ 7,172 Asset impairments and other costs, net of gains on sale (asset-related) (3,298 ) (3,298 ) Total $ 3,874 $ 3,874 The following table presents the components of restructuring costs and where they are recorded within our statement of operations and comprehensive loss (in thousands): Year Ended December 31, 2020 Year Ended December 31, 2019 Employee- related Asset- related Total Employee- related Asset- related Total Research and development $ 1,770 $ (5,385 ) $ (3,615 ) $ 4,126 $ 2,087 $ 6,213 General and administrative 874 — 874 402 — 402 Total $ 2,644 $ (5,385 ) $ (2,741 ) $ 4,528 $ 2,087 $ 6,615 The following table presents the employee-related activity in the accrued personnel-related expense liability (in thousands): Year Ended December 31, 2020 2019 Balance at beginning of year $ 1,182 $ — Charges 2,644 4,528 Cash payments (3,826 ) (3,346 ) Balance at end of year $ — $ 1,182

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Event	15. Subsequent Event On March 4, 2021, we entered into an Agreement and Plan of Merger, or the merger agreement, with Amgen Inc., or Amgen, and Franklin Acquisition Sub, Inc., or the purchaser, pursuant to which, and upon the terms and subject to the conditions thereof, Amgen agreed to cause the purchaser to commence a cash tender offer to purchase all outstanding shares of our common stock, par value $0.001 per share, at a price of $38.00 per share in cash, minus any applicable withholding taxes and without interest. Following the completion of the tender offer, the purchaser will merge with us, with us continuing as the surviving corporation and a wholly owned subsidiary of Amgen. At the effective time of the merger, each share (other than shares validly tendered and irrevocably accepted for purchase pursuant to the offer, excluded shares and dissenting shares (each as defined in the merger agreement)) will be converted into the right to receive an amount in cash equal to the offer price, without interest, minus any required withholding of taxes. The offer to purchase all outstanding shares of our common stock represents an equity value of approximately $ 1.9 billion. The transaction is expected to close by the end of the second quarter of 2021 and is subject to customary closing conditions, as described in that Current Report on Form 8-K with the SEC on March 4, 2021. The offer will initially remain open for 20 business days from the date of commencement of the offer. If at the scheduled expiration time of the offer any of the conditions to the offer have not been satisfied (unless such condition is waivable by Amgen or the purchaser and has been waived), the purchaser, at its discretion, may extend, and at our request, the purchaser will extend, the offer to permit the satisfaction of all offer conditions. On March 18, 2021, Elaine Wang, a purported stockholder of the company, commenced an action in the United States District Court for the District of Delaware, captioned Elaine Wang v. Five Prime Therapeutics, Inc. et al., Case No. 1:21-cv-00395-UNA, against the company and the current members of our board of directors asserting claims under Sections 14(e), 14(d)(4), and 20(a) of the Securities Exchange Act of 1934 challenging the adequacy of certain public disclosures made by us concerning our proposed transaction with Amgen. The lawsuit seeks, among other things, an injunction preventing consummation of the proposed transaction with Amgen, rescission of the proposed transaction or rescissory damages in the event it is consummated, an accounting by the defendants for all damages caused to the plaintiff, and the award of attorneys’ fees and expenses. Defendants have not been served with nor have they answered the complaint. Defendants believe the claims asserted in the complaint are without merit.

Selected Quarterly Financial In

Selected Quarterly Financial Information	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information	16. Selected Quarterly Financial Information The following amounts are in thousands, except per share amounts: Quarter Ended March 31, June 30, September 30, December 31, 2020 2020 2020 2020 (Unaudited) Revenue $ 8,414 $ 3,424 $ 2,048 $ (708 ) Net loss (20,116 ) (16,937 ) (26,423 ) (20,852 ) Basic and diluted net loss per share (0.57 ) (0.48 ) (0.74 ) (0.51 ) Quarter Ended March 31, June 30, September 30, December 31, 2019 2019 2019 2019 (Unaudited) Revenue $ 5,347 $ 3,333 $ 2,984 $ 3,210 Net loss (35,385 ) (34,391 ) (36,069 ) (31,357 ) Basic and diluted net loss per share (1.02 ) (0.99 ) (1.03 ) (0.89 ) Basic and diluted per share amounts are 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 per share amounts.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles , or GAAP Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable.
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 recorded at face value, or cost, which approximates 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 into in December 2016. The certificate of deposit has a term of one month. We are required to maintain this restricted cash balance, the amount of which is subject to reduction starting on January 1, 2023, if certain conditions are met, for the duration of this 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, which is part of other income, net. 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. 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 Measurements We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify assets as Level 3 within the valuation hierarchy. We had a non-recurring Level 3 fair value measurement as of December 31, 2020 related to our operating lease right-of-use asset and related leasehold improvements and furniture and fixtures as part of an impairment review in connection with our entry into a sublease agreement, or the facility sublease, with Sutro Biopharma, Inc., or Sutro, pursuant to which we sublet to Sutro office and laboratory space at our current facilities. See Note 5 for additional information regarding the facility sublease and asset group. The following tables summarize 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, 2020 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Money market funds $ 21,250 $ 21,250 $ — $ — U.S. Treasury securities 157,621 157,621 — — Agency bonds 14,991 14,991 — — Commercial paper 53,222 — 53,222 — Certificate of deposit 1,543 — 1,543 — Total $ 248,627 $ 193,862 $ 54,765 $ — December 31, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Money market funds $ 21,706 $ 21,706 $ — $ — U.S. Treasury securities 35,498 35,498 — — Agency bonds 48,834 48,834 — — Corporate bonds 1,800 — 1,800 — Commercial paper 19,195 — 19,195 — Certificate of deposit 1,543 — 1,543 — Total $ 128,576 $ 106,038 $ 22,538 $ —
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 are reviewed for impairment whenever events or changes in circumstances indicate that the assets may not be recoverable. Recoverability of these assets is measured by comparing their carrying amounts to the future undiscounted cash flows the assets are expected to generate. If an asset is impaired, the impairment to be recognized equals the amount by which the carrying value exceeds the asset’s fair value. The primary measure of fair value is discounted cash flows, which includes significant estimates primarily related to the discount rate and projected cash flows. The discount rate considers the relevant risk associated with asset-specific characteristics and the uncertainty related to the ability to achieve the projected cash flows. In connection with the corporate restructurings that we undertook in 2019: • We entered the facility sublease with Sutro in September 2020 in order to reduce our corporate facilities footprint. Accordingly, we evaluated our operating lease right-of-use asset and related leasehold improvements and furniture and fixtures and determined that the carrying value of this asset group was no longer recoverable. We calculated the fair value of this asset group using discounted cash flows, which have significant unobservable inputs related to discount rate (7%) and projected cash flows. We elected to exclude the operating lease obligation from the asset group when testing whether the carrying amount of the asset group was recoverable. As a result, we classified the fair value of this asset group within Level 3 of the fair value hierarchy. See Note 5 for additional information regarding the facility sublease and this asset group. • We evaluated our laboratory equipment and determined that the carrying value was no longer recoverable. See Note 14 for additional information regarding the laboratory equipment.
Leases	Leases Effective January 1, 2019 , we adopted Financial Accounting Standards Board, or FASB, Accounting Standard Update, or ASU, No. 2016-02, Leases (Topic 842) , or Topic 842. We record a liability to make lease payments and a right-of-use asset for our right to use the underlying assets for the applicable lease terms on our balance sheet. We elected the “package of practical expedients,” which permitted us to not reassess our prior conclusion about lease identification, lease classification, and initial direct costs. We also elected (i) to account on the balance sheet with a lease term at the commencement date of twelve months or less. We determine if an arrangement is a lease at inception date. All our leases are classified as operating leases. Operating lease liabilities and the corresponding right-of-use assets are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. When available, we use the rate implicit in the lease to discount lease payments to present value. However, our leases do not provide a readily determinable implicit rate. Therefore, we must estimate our incremental borrowing rate to discount the lease payments based on information available at lease commencement. We include options to extend the lease in our lease liability and right-of-use asset when it is reasonably certain that we will exercise the option. Our lease agreements do not contain any material residual value guarantees or material restrictive covenants . We recognize operating lease cost as a single lease cost on a straight-line basis. However, once a right-of-use asset is impaired, lease cost for the arrangement that generated that right-of-use asset is no longer recognized on a straight-line basis due to variability in the interest amortization. Variable lease payments primarily include building operating expenses as charged to us by our landlords and are not included in the lease liability; rather, they are recognized on the statement of operations and comprehensive loss in the period in which the obligation is incurred. We recognize sublease income on a straight-line basis. Variable sublease payments are recognized when the corresponding variable lease payments of the underlying master lease are incurred. Sublease income, including the variable sublease payments, are recorded in other income, net on the statement of operations and comprehensive loss.
Restructuring and Other Charges	Restructuring and Other Charges We account for costs related to our restructuring activities in accordance with ASC 420, Exit or Disposal Cost Obligations We will recognize other restructuring costs, including lease or other contract termination costs incurred in connection with terminating a contract before the end of its term, when we terminate the contract in accordance with its terms. See Note 14 for additional information regarding charges related to our corporate restructurings.
Revenue Recognition	Revenue Recognition Effective January 1, 2018, we adopted FASB ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) The terms of our license and collaborative research and development agreements include upfront and license fees, research, development and other funding or reimbursements, milestone and other contingent payments for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of commercialized products. Arrangements that include upfront payments may require deferral of revenue recognition to a future period until we perform obligations under these arrangements. We record research and development funding payable to us as accounts receivable when our right to consideration is unconditional. The event-based milestone and other contingent payments represent variable consideration, and we use the most likely amount method to estimate this variable consideration . Given the high degree of uncertainty around the occurrence of these events, we determine the milestone and other contingent amounts to be fully constrained until the uncertainty associated with these payments is resolved. We will recognize revenue from sales-based royalty payments when or as the sales occur. We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. A performance obligation is a promise in a contract to transfer a distinct good or service and is the unit of accounting in Topic 606. A contract’s transaction price is allocated among each distinct performance obligation based on relative standalone selling price and recognized as revenue when, or as, the applicable performance obligation is satisfied. Under Topic 606, we elected to use the practical expedient permitted related to adoption, which does not require us to disclose certain information regarding our remaining performance obligations as of the end of the reporting period prior to the initial date of adoption. Additionally, we elected the practical expedient for certain research and development funding which allows us to recognize revenue in the amount for which we have a right to invoice if our right to consideration is an amount that corresponds directly to the value of our performance completed to date. As a result, we effectively bypass the steps of determining the transaction price and allocating that transaction price to the performance obligation .
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. 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 and contract research organizations, or CROs, and clinical manufacturing organizations, or CMOs, that conduct and manage preclinical studies and clinical trials on our behalf based on actual time and expenses incurred by such entities. Further, we accrue expenses related to clinical trials based on the level of patient activity according to the relevant 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. 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 awards, or RSAs, and stock option awards. We have granted RSAs, some of which are subject to performance conditions or market conditions. For RSAs with only service conditions, stock-based compensation cost is based on the closing market price of our common stock at the date of grant and is recognized as expense ratably over the requisite service period. For RSAs subject to performance conditions, stock-based compensation cost is calculated similarly and is recognized as expense using the accelerated attribution recognition method when it is probable that the performance condition will be achieved. For RSAs subject to market conditions, we base the fair value of the awards on a Monte Carlo simulation model and recognize stock-based compensation cost commencing at the grant date over the derived service period. Performance- and market-based awards require estimates as to the probability of certain outcomes—the probability of the achievement of performance conditions and the probability of various market-based outcomes, respectively—which require a high degree of judgment. For stock option awards, stock-based compensation cost is measured at the grant date, based on the fair value 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 account for forfeitures as they occur by reversing any expense recognized for unvested awards.
Employee Benefit Plan	Employee Benefit Plan We have a 401(k) Plan for all of our employees. Eligible employees may contribute through payroll deductions, and we may match the employees’ 401(k) contributions, at our discretion and not to exceed a prescribed annual limit per employee. Under this matching program, we contributed $0.3 million, $0.7 million and $1.0 million for the years ended December 31, 2020, 2019 and 2018, respectively.
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. Valuation allowances are provided when the expected realization of the deferred tax assets does not meet the more-likely-than-not criteria. This assessment requires a high degree of judgment. As a result, deferred tax assets at the end of 2020 and 2019 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.
Accounting Pronouncements Recently Adopted	Accounting Pronouncements Recently Adopted Leases In February 2016, FASB issued Topic 842, which amended existing guidance to require substantially all leases to be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability, including leases currently accounted for as operating leases. We adopted Topic 842, effective January 1, 2019, using the updated modified retrospective transition method, in which the new standard is applied as of the date of initial adoption. We recognized and measured agreements executed prior to the date of initial adoption that were considered leases on January 1, 2019. No cumulative effect adjustment of initially applying the standard to the opening balance of retained earnings was made upon adoption. Upon adoption, we derecognized $19.8 million in deferred rent and ecognized $52.5 million in lease liabilities and $33.3 million in right-of-use assets on our balance sheet Revenue recognition In November 2018, FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808) clarifies when certain transactions between collaborative arrangement participants should be accounted for under Topic 606 and incorporates unit-of-account guidance consistent with Topic 606 to aid in this determination. We adopted ASU 2018-18, effective January 1, 2020, to be applied retrospectively to the date of initial application of Topic 606. The adoption of ASU 2018-18 had no effect on our financial statements and disclosures. In May 2014, FASB issued Topic 606, which superseded nearly all existing revenue recognition guidance under GAAP. We adopted Topic 606, effective January 1, 2018, using the modified retrospective transition method, in which the new standard is applied as of the date of initial adoption. We applied the standard to contracts that were not completed at the date of initial application. We recorded the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings. The adoption of Topic 606 resulted in a decrease of $1.4 million to deferred revenue and an increase of $1.4 million to retained earnings as of January 1, 2018. Our adoption of Topic 606 effective January 1, 2018 affected the following financial statement line items (in thousands, except per share data): Year Ended December 31, 2018 Condensed Statement of Operations and Comprehensive Loss Under Topic 606 Under Topic 605 Effect of change Collaboration and license revenue $ 49,868 $ 52,329 $ (2,461 ) Operating expenses 196,023 196,023 — Operating loss (146,155 ) (143,694 ) (2,461 ) Net loss (140,447 ) (137,986 ) (2,461 ) Net loss per share - basic and diluted (4.13 ) (4.06 ) (0.07 ) Year Ended December 31, 2018 Condensed Statement of Cash Flows Under Topic 606 Under Topic 605 Effect of change Net loss $ (140,447 ) $ (137,986 ) $ (2,461 ) Decrease in deferred revenue 1,373 — 1,373 Changes in operating assets and liabilities: Receivables from collaborative partner 8,037 8,037 — Deferred revenue (11,043 ) (12,131 ) 1,088 Cash, cash equivalents and restricted cash: At beginning of period 61,333 61,333 — At end of period 45,496 45,496 — Other In August 2018, FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework In June 2016, FASB issued ASU No. 2016-13, Financial Instruments–Credit Losses (Topic 326) In April 2015, FASB issued ASU No. 2018-15, Intangibles–Goodwill and Other–Internal-Use Software (Topic 350)
Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Not Yet Adopted In December 2019, FASB issued ASU No. 2019-12, Income Taxes–Simplifying the Accounting for Income Taxes (Topic 740) We do not anticipate that the adoption of ASU 2019-12 will have a material effect on our financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Summary Of Significant Accounting Policies [Line Items]
Summary of Financial Instruments Measured at Fair Value	The following tables summarize 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, 2020 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Money market funds $ 21,250 $ 21,250 $ — $ — U.S. Treasury securities 157,621 157,621 — — Agency bonds 14,991 14,991 — — Commercial paper 53,222 — 53,222 — Certificate of deposit 1,543 — 1,543 — Total $ 248,627 $ 193,862 $ 54,765 $ — December 31, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Money market funds $ 21,706 $ 21,706 $ — $ — U.S. Treasury securities 35,498 35,498 — — Agency bonds 48,834 48,834 — — Corporate bonds 1,800 — 1,800 — Commercial paper 19,195 — 19,195 — Certificate of deposit 1,543 — 1,543 — Total $ 128,576 $ 106,038 $ 22,538 $ —
ASU 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Summary of Guidance Effect under Topic 605 before Adoption of Topic 606 on Financial Statement	Our adoption of Topic 606 effective January 1, 2018 affected the following financial statement line items (in thousands, except per share data): Year Ended December 31, 2018 Condensed Statement of Operations and Comprehensive Loss Under Topic 606 Under Topic 605 Effect of change Collaboration and license revenue $ 49,868 $ 52,329 $ (2,461 ) Operating expenses 196,023 196,023 — Operating loss (146,155 ) (143,694 ) (2,461 ) Net loss (140,447 ) (137,986 ) (2,461 ) Net loss per share - basic and diluted (4.13 ) (4.06 ) (0.07 ) Year Ended December 31, 2018 Condensed Statement of Cash Flows Under Topic 606 Under Topic 605 Effect of change Net loss $ (140,447 ) $ (137,986 ) $ (2,461 ) Decrease in deferred revenue 1,373 — 1,373 Changes in operating assets and liabilities: Receivables from collaborative partner 8,037 8,037 — Deferred revenue (11,043 ) (12,131 ) 1,088 Cash, cash equivalents and restricted cash: At beginning of period 61,333 61,333 — At end of period 45,496 45,496 —

Cash Equivalents and Marketab_2

Cash Equivalents and Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2020
Cash And Cash Equivalents [Abstract]
Summary of Cash Equivalents and Marketable Securities	The following is a summary of our cash equivalents and marketable securities (in thousands): December 31, 2020 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 21,250 $ — $ — $ 21,250 U.S. Treasury securities 157,642 3 (24 ) 157,621 Agency bonds 14,998 — (7 ) 14,991 Commercial paper 53,219 4 (1 ) 53,222 Total cash equivalents and marketable securities 247,109 7 (32 ) 247,084 Less: cash equivalents (29,247 ) — — (29,247 ) Total marketable securities $ 217,862 $ 7 $ (32 ) $ 217,837 December 31, 2019 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 21,706 $ — $ — $ 21,706 U.S. Treasury securities 35,471 27 — 35,498 Agency bonds 48,790 44 — 48,834 Corporate bonds 1,800 — — 1,800 Commercial paper 19,188 7 — 19,195 Total cash equivalents and marketable securities 126,955 78 — 127,033 Less: cash equivalents (26,453 ) — — (26,453 ) Total marketable securities $ 100,502 $ 78 $ — $ 100,580
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	As of December 31, 2020, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Debt securities maturing: In one year or less $ 185,783 $ 185,759 In one to two years 32,079 32,078 Total marketable securities $ 217,862 $ 217,837
Summary of Marketable Securities In Continuous Unrealized Loss Position	The following table summarizes our marketable securities in a continuous unrealized loss position as of December 31, 2020 (in thousands): Amortized Unrealized Estimated Cost Basis Losses Fair Value Less than 12 months: U.S. Treasury securities $ 133,822 $ (24 ) $ 133,798 Agency bonds 14,998 (7 ) 14,991 Commercial paper 19,981 (1 ) 19,980 Total $ 168,801 $ (32 ) $ 168,769

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Components of Property and Equipment	Property and equipment consist of the following (in thousands): December 31, 2020 2019 Computer equipment and software $ 1,981 $ 2,281 Furniture and fixtures 842 968 Laboratory equipment 913 4,219 Leasehold improvements 17,265 22,175 21,001 29,643 Less: accumulated depreciation and amortization (9,792 ) (7,109 ) Property and equipment, net $ 11,209 $ 22,534

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Summary of Lease Cost, Income and Related Supplemental Information	The tables below present lease cost, income and related supplemental information (in thousands, except as otherwise indicated): Year Ended December 31, 2020 2019 Lease cost (as lessee): Operating lease cost $ 6,614 $ 6,140 Variable lease cost 2,418 1,762 Total lease cost $ 9,032 $ 7,902 Lease income (as lessor): Operating sublease income $ 1,146 $ — Supplemental cash flow information (as lessee): Cash paid for amounts included in the measurement of operating lease liabilities $ 7,855 $ 6,693 December 31, 2020 2019 Supplemental balance sheet information (as lessee): Weighted-average remaining lease term (in years) 6.8 8.0 Weighted-average discount rate (%) 7.33 % 7.44 %
Summary of Undiscounted Cash Flows to Operating Lease Liabilities	For the facility leases, the undiscounted cash flows are reconciled to the operating lease liabilities recorded on the balance sheet, as follows (in thousands): Facility Leases (1) Facility Sublease 2021 $ 8,389 $ 2,547 2022 8,652 — 2023 8,569 6,310 2024 8,341 7,476 2025 8,632 7,737 2026 and beyond 18,194 16,297 Total minimum lease payments 60,777 $ 40,367 Less: amount of lease payments representing interest (13,343 ) Present value of future minimum lease payments 47,434 Less: operating lease obligations, current portion (5,125 ) Operating lease obligations, long-term portion $ 42,309 (1)

Other Accrued Liabilities (Tabl

Other Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Schedule of Other Accrued Liabilities	Other accrued liabilities consist of the following (in thousands): December 31, 2020 2019 Clinical development $ 6,521 $ 7,787 Manufacturing 2,193 540 Accrued trade payable 2,341 1,087 Other 330 245 Total accrued liabilities $ 11,385 $ 9,659

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Option Activity under Stock Plans and Related Information	The following table summarizes option activity and related information under the 2013 Plan and the Prior Plans: 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, 2020 3,314,722 $ 20.50 Options granted 2,000,502 $ 4.37 Options exercised (465,024 ) $ 8.43 Options forfeited (218,564 ) $ 9.65 Options expired (432,309 ) $ 34.30 Balance at December 31, 2020 4,199,327 $ 13.30 7.5 $ 33,125 Exercisable at December 31, 2020 2,298,658 $ 19.38 6.3 $ 11,787
Schedule of Restricted Stock Award Activity under 2013 Plan and Related Information	We have granted RSAs, which are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting and are not forfeitable once fully vested. The following table summarizes RSA activity and related information under the 2013 Plan: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at January 1, 2020 1,060,577 $ 11.24 RSAs granted 614,950 $ 4.91 RSAs vested (678,076 ) $ 11.06 RSAs forfeited (228,162 ) $ 10.84 Unvested balance at December 31, 2020 769,289 $ 6.46
Schedule of Stock-Based Compensation Expenses Recognized	Total stock-based compensation expense recognized was as follows (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 3,279 $ 8,041 $ 15,426 General and administrative 6,908 14,774 14,042 Total $ 10,187 $ 22,815 $ 29,468
Schedule of Stock Options 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, 2020 2019 2018 2020 2019 2018 Expected term (years) 5.0-6.3 5.0-6.3 5.5-6.3 0.5 0.5 0.5 Expected volatility 69-73% 67-68% 68-70% 107-199% 64-67% 47-94% Risk-free interest rate 0.4-1.3% 1.6-2.5% 2.6-2.9% 0.1-0.2% 1.6-2.4% 1.4-2.5% 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, 2020
Earnings Per Share [Abstract]
Securities Excluded from Calculation of Diluted Net Loss Per Share	We excluded the following securities from the calculation of diluted per share amounts as the effect would have been antidilutive (in thousands): Year Ended December 31, 2020 2019 2018 Options to purchase common stock 4,633 3,760 3,710 RSAs 1,109 1,273 880 Total 5,742 5,033 4,590

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	12 Months Ended
	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Summary of Changes in Balances of Contract Assets and Contract Liabilities	The following tables present changes in the balances of our contract assets, including receivables from collaboration partners, and contract liabilities, including deferred revenue (in thousands): Contract Assets Balance at January 1, 2020 $ 4,097 Additions 4,023 Deductions (8,035 ) Balance at December 31, 2020 $ 85 Contract Liabilities Balance at January 1, 2020 $ 6,409 Additions for advance billings 1,190 Deductions for performance obligations satisfied: In current period (4,516 ) In prior periods related to measure of progress updates (1,026 ) Balance at December 31, 2020 $ 2,057
Schedule of License and Collaboration Revenue by Collaboration Partner or Licensee	The following table presents license and collaboration revenue by collaboration partner or licensee (in thousands): Year Ended December 31, 2020 2019 2018 Milestone payments: (1) Cabiralizumab Collaboration - BMS $ — $ — $ 25,000 Other payments: China Collaboration - Zai Lab 5,455 4,385 5,068 Cabiralizumab Collaboration - BMS 2,649 9,060 13,441 Immuno-oncology Research Collaboration - BMS — 1,429 6,086 License Agreement - Seagen 5,074 — — Other — — 273 Total $ 13,178 $ 14,874 $ 49,868 (1)

Other Income, Net (Tables)

Other Income, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Other Income And Expenses [Abstract]
Schedule of other income, net	The components of our other income, net were as follows (in thousands): Year Ended December 31, 2020 2019 2018 Interest income (see Note 3) $ 820 $ 4,740 $ 5,792 Sublease income (see Note 5) 1,146 — — Other (54 ) (4 ) (84 ) Total $ 1,912 $ 4,736 $ 5,708

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The components of our income tax expense (benefit) were as follows (in thousands): Year Ended December 31, 2020 2019 2018 Current tax benefit Federal $ (6,630 ) $ — $ — State — — — Total current tax benefit (6,630 ) — — Deferred tax expense Federal — — — State — — — Total deferred tax expense — — — Total tax benefit $ (6,630 ) $ — $ —
Schedule of Income Tax Expense (Benefit) Differs from Amount Computed by Applying Statutory Federal Income Tax Rate	The income tax expense (benefit) differs from the amount computed by applying the statutory federal income tax rate as follows (in thousands): Year Ended December 31, 2020 2019 2018 Federal statutory income tax $ (19,102 ) $ (28,812 ) $ (29,495 ) State statutory income tax 1 1 1 Stock compensation 1,966 4,055 3,698 Nontaxable equity premiums — (20 ) (85 ) Change in valuation allowance 17,754 32,540 38,953 Income from shareholder 3,513 — — Research and orphan drug credits (4,701 ) (8,015 ) (13,192 ) Tax benefit from alternative minimum tax credit refund (6,630 ) — — Other permanent items 569 251 120 Income tax benefit $ (6,630 ) $ — $ —
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences and carryforwards that give rise to significant portions of deferred tax assets and liabilities consist of the following (in thousands): December 31, 2020 2019 Net operating loss carryforwards $ 94,763 $ 85,928 Research and orphan drug credits 73,608 68,053 Deferred revenue 122 1,372 Stock-based compensation 5,390 7,562 Capitalized license and depreciation basis differences 2,906 3,196 Reserves, accruals and tenant improvement allowances 1,090 1,389 Operating lease liability 10,158 10,619 Total deferred tax assets 188,037 178,119 Less: valuation allowance (182,319 ) (168,691 ) Net deferred tax assets 5,718 9,428 Capitalized license and depreciation basis differences (808 ) (2,374 ) Operating right-of-use asset (4,557 ) (6,621 ) Prepaid expenses (353 ) (433 ) Total deferred tax liabilities (5,718 ) (9,428 ) Total net deferred tax assets $ — $ —
Schedule of Reconciliation of Unrecognized Tax Benefits	A reconciliation of our unrecognized tax benefits is as follows (in thousands): Year Ended December 31, 2020 2019 2018 Balance at beginning of year $ 18,393 $ 16,660 $ 13,584 Additions for prior year tax positions — 11 622 Additions for current year tax positions 1,020 1,722 2,454 Balance at end of year $ 19,413 $ 18,393 $ 16,660

Restructuring and Other Charg_2

Restructuring and Other Charges (Tables)	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Summary of Management's Expected and Actual Costs	The following table summarizes management’s estimates of costs that were expected to be incurred and were probable as of December 31, 2020 and the actual costs incurred to date through December 31, 2020 (in thousands): Total Estimated Restructuring Costs Total Restructuring Costs Incurred to Date Employee retention, severance and termination benefits (employee-related) $ 7,172 $ 7,172 Asset impairments and other costs, net of gains on sale (asset-related) (3,298 ) (3,298 ) Total $ 3,874 $ 3,874
Summary of Components of Restructuring Costs that are Recorded within Statement of Operations and Comprehensive Loss	The following table presents the components of restructuring costs and where they are recorded within our statement of operations and comprehensive loss (in thousands): Year Ended December 31, 2020 Year Ended December 31, 2019 Employee- related Asset- related Total Employee- related Asset- related Total Research and development $ 1,770 $ (5,385 ) $ (3,615 ) $ 4,126 $ 2,087 $ 6,213 General and administrative 874 — 874 402 — 402 Total $ 2,644 $ (5,385 ) $ (2,741 ) $ 4,528 $ 2,087 $ 6,615
Summary of Employee-related Activity In Accrued Personnel-related Expense Liability	The following table presents the employee-related activity in the accrued personnel-related expense liability (in thousands): Year Ended December 31, 2020 2019 Balance at beginning of year $ 1,182 $ — Charges 2,644 4,528 Cash payments (3,826 ) (3,346 ) Balance at end of year $ — $ 1,182

Selected Quarterly Financial _2

Selected Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2020 2020 2020 (Unaudited) Revenue $ 8,414 $ 3,424 $ 2,048 $ (708 ) Net loss (20,116 ) (16,937 ) (26,423 ) (20,852 ) Basic and diluted net loss per share (0.57 ) (0.48 ) (0.74 ) (0.51 ) Quarter Ended March 31, June 30, September 30, December 31, 2019 2019 2019 2019 (Unaudited) Revenue $ 5,347 $ 3,333 $ 2,984 $ 3,210 Net loss (35,385 ) (34,391 ) (36,069 ) (31,357 ) Basic and diluted net loss per share (1.02 ) (0.99 ) (1.03 ) (0.89 )

Business - Additional Informati

Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	Jan. 01, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Certificate of deposit term		1 month
Fair value, assets, level 1 to level 2 transfers		$ 0
Fair value, assets, level 2 to level 1 transfer		$ 0
Discount rate		7.00%
Amount contribution under employee benefit plan		$ 300,000	$ 700,000	$ 1,000,000
Right-of use assets		21,276,000	30,934,000
Decrease to deferred revenue				1,373,000
Increase to retained earnings		(516,211,000)	$ (431,883,000)
ASU 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Decrease to deferred revenue	$ 1,400,000			$ 1,373,000
Increase to retained earnings	$ 1,400,000
ASU 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred rent derecognized		19,800,000
Lease liability		52,500,000
Right-of use assets		$ 33,300,000
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

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	$ 248,627	$ 128,576
Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	21,250	21,706
Agency Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	14,991	48,834
Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	53,222	19,195
Certificate of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1,543	1,543
Corporate bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		1,800
U.S. Treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
U.S. Treasury securities	157,621	35,498
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	193,862	106,038
Level 1 [Member] | Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	21,250	21,706
Level 1 [Member] | Agency Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	14,991	48,834
Level 1 [Member] | U.S. Treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
U.S. Treasury securities	157,621	35,498
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	54,765	22,538
Level 2 [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	53,222	19,195
Level 2 [Member] | Certificate of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 1,543	1,543
Level 2 [Member] | Corporate bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		$ 1,800

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Summary of Guidance Effect under Topic 605 before Adoption of Topic 606 on Condensed Statement of Operations and Comprehensive Loss (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Collaboration and license revenue		$ 2,048	$ 3,424	$ 8,414	$ 3,210	$ 2,984	$ 3,333	$ 5,347	$ 13,178	$ 14,874	$ 49,868
Operating expenses									106,048	156,812	196,023
Operating loss									(92,870)	(141,938)	(146,155)
Net loss	$ (20,852)	$ (26,423)	$ (16,937)	$ (20,116)	$ (31,357)	$ (36,069)	$ (34,391)	$ (35,385)	$ (84,328)	$ (137,202)	$ (140,447)
Net loss per share - basic and diluted	$ (0.51)	$ (0.74)	$ (0.48)	$ (0.57)	$ (0.89)	$ (1.03)	$ (0.99)	$ (1.02)	$ (2.29)	$ (3.92)	$ (4.13)
ASU 2014-09 [Member] | Under Topic 605 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Collaboration and license revenue											$ 52,329
Operating expenses											196,023
Operating loss											(143,694)
Net loss											$ (137,986)
Net loss per share - basic and diluted											$ (4.06)
ASU 2014-09 [Member] | Effect of change [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Collaboration and license revenue											$ (2,461)
Operating loss											(2,461)
Net loss											$ (2,461)
Net loss per share - basic and diluted											$ (0.07)

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Guidance Effect under Topic 605 before Adoption of Topic 606 on Condensed Statement of Cash Flows (Detail) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net loss		$ (20,852)	$ (26,423)	$ (16,937)	$ (20,116)	$ (31,357)	$ (36,069)	$ (34,391)	$ (35,385)	$ (84,328)	$ (137,202)	$ (140,447)
Decrease in deferred revenue												1,373
Changes in operating assets and liabilities:
Receivables from collaborative partners										$ 4,012	999	8,037
Deferred revenue												(11,043)
Cash, cash equivalents and restricted cash:
At beginning of period	$ 61,333								45,496		45,496	61,333
At end of period												45,496
ASU 2014-09 [Member] | Under Topic 605 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net loss												(137,986)
Changes in operating assets and liabilities:
Receivables from collaborative partners												8,037
Deferred revenue												(12,131)
Cash, cash equivalents and restricted cash:
At beginning of period	61,333								$ 45,496		$ 45,496	61,333
At end of period												45,496
ASU 2014-09 [Member] | Effect of change [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net loss												(2,461)
Decrease in deferred revenue	$ 1,400											1,373
Changes in operating assets and liabilities:
Deferred revenue												$ 1,088

Cash Equivalents and Marketab_3

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 217,862	$ 100,502
Unrealized Gains	7	78
Unrealized Losses	(32)
Estimated Fair Value	217,837	100,580
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	21,250	21,706
Estimated Fair Value	21,250	21,706
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	157,642	35,471
Unrealized Gains	3	27
Unrealized Losses	(24)
Estimated Fair Value	157,621	35,498
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	14,998	48,790
Unrealized Gains		44
Unrealized Losses	(7)
Estimated Fair Value	14,991	48,834
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		1,800
Estimated Fair Value		1,800
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	53,219	19,188
Unrealized Gains	4	7
Unrealized Losses	(1)
Estimated Fair Value	53,222	19,195
Total cash equivalents and marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	247,109	126,955
Unrealized Gains	7	78
Unrealized Losses	(32)
Estimated Fair Value	247,084	127,033
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	(29,247)	(26,453)
Estimated Fair Value	$ (29,247)	$ (26,453)

Cash Equivalents and Marketab_4

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, 2020	Dec. 31, 2019
Available For Sale Securities Debt Maturities [Abstract]
Amortized Cost, In one year or less	$ 185,783
Amortized Cost, In one to two years	32,079
Amortized Cost Basis	217,862	$ 100,502
Estimated Fair Value, In one year or less	185,759
Estimated Fair Value, In one to two years	32,078
Total marketable securities, Estimated Fair Value	$ 217,837	$ 100,580

Cash Equivalents and Marketab_5

Cash Equivalents and Marketable Securities - Summary of Marketable Securities In Continuous Unrealized Loss Position (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized cost basis	$ 168,801
Unrealized losses	(32)
Estimated fair value	168,769
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost basis	133,822
Unrealized losses	(24)
Estimated fair value	133,798
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost basis	14,998
Unrealized losses	(7)
Estimated fair value	14,991
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost basis	19,981
Unrealized losses	(1)
Estimated fair value	$ 19,980

Cash Equivalents and Marketab_6

Cash Equivalents and Marketable Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020USD ($)Security	Dec. 31, 2019Security
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized loss position		0
Sales of available-for-sale securities | $	$ 0
Cash equivalents and marketable securities average maturity period	8 months
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized loss position	14
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized loss position	1
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized loss position	2
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents and marketable securities maturity period	18 months

Property and Equipment - Compon

Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 21,001	$ 29,643
Less: accumulated depreciation and amortization	(9,792)	(7,109)
Property and equipment, net	11,209	22,534
Computer equipment and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,981	2,281
Furniture and fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	842	968
Laboratory equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	913	4,219
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 17,265	$ 22,175

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2018Instrument	Dec. 31, 2020USD ($)ft²Floor	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Lessee Lease Description [Line Items]
Lease term		10 years
Lease option additional extend term		5 years
Rent commencement date		Jan. 1, 2018
Percentage of rent reduction in first six months		50.00%
Additional lease requirements		In addition, the corporate facility lease required us to deliver an irrevocable standby letter of credit in an amount of $1.5 million to the landlord for the period commencing on the effective date of the corporate facility lease until at least 60 days after the expiration of the lease, subject to 50% reduction on January 1, 2023 if certain conditions are met.
Impairment loss		$ 8,792
Research and development costs		65,491	$ 114,063	$ 156,352
General and administrative costs		40,557	42,749	39,671
Operating lease, right-of-use assets		$ 21,276	$ 30,934
Rent Expense				$ 5,900
Lab Lease Agreement [Member]
Lessee Lease Description [Line Items]
Lease term		2 years 8 months 1 day
Lease option additional extend term		2 months
Rent commencement date		Nov. 1, 2020
Bemarituzumab Programs [Member]
Lessee Lease Description [Line Items]
Number of sequencing instruments | Instrument	4
Termination of lease instruments date	2020
Accrued gain on lease termination		$ 700
Sub Lease Agreement with Sutro [Member]
Lessee Lease Description [Line Items]
Lease term		6 years 6 months
Rent commencement date		Jul. 2, 2021
Office and laboratory space (in square feet) | ft²		115,466
Number of floors in the premises | Floor		4
Number of floors sublet | Floor		3
Impairment loss		$ 13,800
Research and development costs		7,300
General and administrative costs		6,500
Operating lease, right-of-use assets		20,100
Impairment loss adjusted the carrying values of leasehold improvements		11,200
Impairment loss adjusted the carrying values of furniture and fixtures		300
Irrevocable Standby Letter of Credit [Member]
Lessee Lease Description [Line Items]
Letter of credit		$ 1,500

Leases - Summary of Lease Cost,

Leases - Summary of Lease Cost, Income and Related Supplemental Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease cost (as lessee):
Operating lease cost	$ 6,614	$ 6,140
Variable lease cost	2,418	1,762
Total lease cost	9,032	7,902
Lease income (as lessor):
Operating sublease income	1,146
Supplemental information
Cash paid for amounts included in the measurement of operating lease liabilities	$ 7,855	$ 6,693
Supplemental balance sheet information (as lessee):
Weighted-average remaining lease term (in years)	6 years 9 months 18 days	8 years
Weighted-average discount rate (%)	7.33%	7.44%

Leases - Summary of Undiscounte

Leases - Summary of Undiscounted Cash Flows to Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Lessee Lease Description [Line Items]
Less: operating lease obligations, current portion	$ (5,125)	$ (4,080)
Operating lease obligations, long-term portion	42,309	$ 45,532
Facility Lease [Member]
Lessee Lease Description [Line Items]
2021	8,389
2022	8,652
2023	8,569
2024	8,341
2025	8,632
2026 and beyond	18,194
Total minimum lease payments	60,777
Less: amount of lease payments representing interest	(13,343)
Present value of future minimum lease payments	47,434
Less: operating lease obligations, current portion	(5,125)
Operating lease obligations, long-term portion	42,309
Facility Sublease [Member]
Lessee Lease Description [Line Items]
2021	2,547
2023	6,310
2024	7,476
2025	7,737
2026 and beyond	16,297
Total minimum lease payments	$ 40,367

Other Accrued Liabilities - Sch

Other Accrued Liabilities - Schedule of Other Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Clinical development	$ 6,521	$ 7,787
Manufacturing	2,193	540
Accrued trade payable	2,341	1,087
Other	330	245
Total accrued liabilities	$ 11,385	$ 9,659

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail)	Jul. 29, 2019Employee$ / sharesshares	Nov. 30, 2020USD ($)shares	Aug. 31, 2020USD ($)	Jan. 31, 2018USD ($)shares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / shares	Jan. 01, 2020shares	Jul. 01, 2019$ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized capital stock issuable					110,000,000
Common stock, par value | $ / shares					$ 0.001	$ 0.001
Common stock, shares authorized					100,000,000	100,000,000
Preferred stock, par value | $ / shares					$ 0.001	$ 0.001
Preferred stock, shares authorized					10,000,000	10,000,000
Issuance of stock, Shares		8,280,000		5,897,435
Gross proceeds from issuance of common stocks | $		$ 163,400,000		$ 115,000,000	$ 163,447,000		$ 115,000,000
Proceeds from follow-on public offering of common stock, net of issuance costs | $		$ 163,200		$ 107,600	163,214,000		$ 107,612,000
Proceeds from disgorgement of stockholder's short-swing profits | $					$ 16,727,000
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 | $ / shares					$ 2.70	$ 4.96	$ 10.85
Total intrinsic value of options exercised | $					$ 4,000,000	$ 100,000	$ 2,400,000
Total unrecognized compensation expense | $					$ 6,200,000
Unrecognized compensation expense expected to recognize, weighted-average period					2 years 8 months 12 days
Stock-based compensation expense | $					$ 7,200,000	14,300,000	17,300,000
Expected dividend yield					0.00%
Exercise price per share, new options granted | $ / shares					$ 4.37
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense | $					$ 2,800,000	8,200,000	11,600,000
Total fair value of share vesting | $					$ 5,200,000	3,700,000	6,200,000
Employees and directors [Member] | Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense expected to recognize, weighted-average period					2 years 3 months 18 days
Total unrecognized compensation expense to unvested employee and director RSAs | $					$ 2,200,000
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					2,657,782
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					1,227,894			0
Percent of annual increase in common stock available for issuance					1.00%
Number of shares of common stock reserved for future issuance					250,000
Unrecognized compensation expense expected to recognize, weighted-average period					4 months 12 days
Stock-based compensation expense | $					$ 200,000	$ 300,000	$ 500,000
Maximum increase in shares reserved for issuance					300,000
Common stock available for issuance, description					Unless our Board provides otherwise, 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 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, 2020, 1,227,894 shares of common stock were available for issuance under the ESPP.
Purchase price per share as a percentage of fair market value of our common stock					85.00%
Shares issued under ESPP					79,828
Total unrecognized compensation expense | $					$ 200,000
Stock Option Exchange Program [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for future issuance	201,229
Stock options granted, expiration term	7 years
Stock option exchange program, description					these employees who held outstanding stock options granted on or before June 6, 2018 with an exercise price equal to or greater than $18.00 per share, or eligible options, the opportunity to tender each eligible option in exchange for a new stock option with modified terms, or new options.
Exercise price per share eligible for exchange for new stock option | $ / shares									$ 18
Maximum number of eligible shares available for issuance	510,932
Number of employees elected to exchange outstanding stock options | Employee	55
Number of shares cancelled in conjunction with the option exchange offer	436,648
Percentage of eligible options to total shares of common stock	85.00%
Number of shares granted for new options	235,419
Exercise price per share, new options granted | $ / shares	$ 5.06
Unamortized expense remaining on the tendered options | $					$ 200,000
Cowen And Company, LLC [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from follow-on public offering of common stock, net of issuance costs | $			$ 7,100,000
Aggregate offering price | $			$ 75,000,000
Underwriters Purchase Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of stock, Shares		1,080,000		769,230

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, 2020USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance | shares	3,314,722
Number of Shares, Options granted | shares	2,000,502
Number of Shares, Options exercised | shares	(465,024)
Number of Shares, Options forfeited | shares	(218,564)
Number of Shares, Options expired | shares	(432,309)
Number of Shares, Ending balance | shares	4,199,327
Number of Shares, Exercisable | shares	2,298,658
Weighted-Average Exercise Price Per Share, Options beginning balance | $ / shares	$ 20.50
Weighted-Average Exercise Price Per Share, Options granted | $ / shares	4.37
Weighted-Average Exercise Price Per Share, Options exercised | $ / shares	8.43
Weighted-Average Exercise Price Per Share, Options forfeited | $ / shares	9.65
Weighted-Average Exercise Price Per Share, Options expired | $ / shares	34.30
Weighted-Average Exercise Price Per Share, Options ending balance | $ / shares	13.30
Weighted-Average Exercise Price Per Share, Exercisable | $ / shares	$ 19.38
Weighted-Average Remaining Contractual Terms, Options ending balance	7 years 6 months
Weighted-Average Remaining Contractual Terms, Exercisable	6 years 3 months 18 days
Aggregate Intrinsic Value, Options ending balance | $	$ 33,125
Aggregate Intrinsic Value, Exercisable | $	$ 11,787

Stockholders' Equity - Schedu_2

Stockholders' Equity - Schedule of Restricted Stock Award Activity under 2013 Plan and Related Information (Detail) - Restricted Stock Awards [Member]	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Unvested, beginning balance | shares	1,060,577
Number of Shares, Granted | shares	614,950
Number of Shares, Vested | shares	(678,076)
Number of Shares, Forfeited | shares	(228,162)
Number of Shares, Unvested, Ending balance | shares	769,289
Weighted-Average Grant-Date Fair Value, Unvested, Beginning balance | $ / shares	$ 11.24
Weighted-Average Grant-Date Fair Value, Granted | $ / shares	4.91
Weighted-Average Grant-Date Fair Value, Vested | $ / shares	11.06
Weighted-Average Grant-Date Fair Value, Forfeited | $ / shares	10.84
Weighted-Average Grant-Date Fair Value, Unvested, Ending balance | $ / shares	$ 6.46

Stockholders' Equity - Schedu_3

Stockholders' Equity - Schedule of Stock-Based Compensation Expenses Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 10,187	$ 22,815	$ 29,468
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	3,279	8,041	15,426
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 6,908	$ 14,774	$ 14,042

Stockholders' Equity - Schedu_4

Stockholders' Equity - Schedule of Stock Option Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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 dividend yield	0.00%	0.00%	0.00%
Minimum [Member] | Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years	5 years	5 years 6 months
Expected volatility	69.00%	67.00%	68.00%
Risk-free interest rate	0.40%	1.60%	2.60%
Maximum [Member] | Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 3 months 18 days	6 years 3 months 18 days	6 years 3 months 18 days
Expected volatility	73.00%	68.00%	70.00%
Risk-free interest rate	1.30%	2.50%	2.90%
ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 months	6 months	6 months
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	0.00%	64.00%	47.00%
Risk-free interest rate	0.00%	1.60%	1.40%
ESPP [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	0.00%	67.00%	94.00%
Risk-free interest rate	0.00%	2.40%	2.50%

Earnings per Share - Securities

Earnings per Share - Securities Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net income (loss) per share	5,742	5,033	4,590
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	4,633	3,760	3,710
RSAs [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net income (loss) per share	1,109	1,273	880

License and Collaboration Agr_3

License and Collaboration Agreements - Summary of Changes in Balances of Contract Assets and Contract Liabilities (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Contract With Customer Asset And Liability [Abstract]
Beginning balance	$ 4,097
Additions	4,023
Deductions	(8,035)
Ending balance	85
Beginning balance	6,409
Additions for advance billings	1,190
Deductions for performance obligations satisfied in current period	(4,516)
Deductions for performance obligations satisfied in prior periods related to measure of progress updates	(1,026)
Ending balance	$ 2,057

License and Collaboration Agr_4

License and Collaboration Agreements - Schedule of License and Collaboration Revenue by Collaboration Partner or Licensee (Detail) - USD ($) $ in Thousands	3 Months Ended							12 Months Ended				57 Months Ended	60 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015	Jun. 30, 2020	Mar. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Other payments	$ 2,048	$ 3,424	$ 8,414	$ 3,210	$ 2,984	$ 3,333	$ 5,347	$ 13,178	$ 14,874	$ 49,868
Cabiralizumab Collaboration Agreement [Member] | Bristol-Myers Squibb Company [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments										25,000
Other payments								2,649	9,060	13,441	$ 350,000	$ 30,000
Zai Lab [Member] | China License and Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Other payments								5,455	4,385	5,068
Immuno-Oncology Collaboration [Member] | Bristol-Myers Squibb Company [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Other payments									$ 1,429	6,086			$ 36,100
License Agreement [Member] | Seagen, Inc [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Other payments								$ 5,074
Other Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Other payments										$ 273

License and Collaboration Agr_5

License and Collaboration Agreements - Additional Information (Detail) - USD ($)	Oct. 14, 2015	Nov. 30, 2020	Jan. 31, 2018	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015	Jun. 30, 2020	Mar. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of stock, Shares		8,280,000	5,897,435
Revenue recognized				$ 2,048,000	$ 3,424,000	$ 8,414,000	$ 3,210,000	$ 2,984,000	$ 3,333,000	$ 5,347,000	$ 13,178,000	$ 14,874,000	$ 49,868,000
Deferred revenue recognized under collaboration arrangement							6,409,000				2,057,000	6,409,000
Bristol-Myers Squibb Company [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front fee	$ 30,000,000										$ 30,000,000
Bristol-Myers Squibb Company [Member] | Immuno-Oncology Collaboration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research collaboration and license agreement entered month and year											2014-03
Up-front fee											$ 20,000,000
Research funding received over the research term											$ 13,700,000
Issuance of stock, Shares											994,352
Equity premium											$ 2,400,000
Transaction price											36,100,000
Adjustments to transaction price											0
Revenue recognized												1,429,000	6,086,000			$ 36,100,000
Deferred revenue recognized under collaboration arrangement							0				0	0
Bristol-Myers Squibb Company [Member] | Immuno-Oncology Collaboration [Member] | Actual Costs Incurred as a Percentage of Total Budgeted Costs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized											$ 0	1,400,000	6,100,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research collaboration and license agreement entered month and year											2015-10
Up-front fee											$ 350,000,000
Adjustments to transaction price											0
Revenue recognized											2,649,000	9,060,000	13,441,000	$ 350,000,000	$ 30,000,000
Deferred revenue recognized under collaboration arrangement							800,000				0	800,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized											1,800,000	4,700,000	6,900,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member] | Actual Costs Incurred as a Percentage of Total Budgeted Costs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized											$ 800,000	4,400,000	6,600,000
Zai Lab [Member] | China License and Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research collaboration and license agreement entered month and year											2017-12
Up-front fee			$ 5,000,000								$ 4,200,000
Research funding received over the research term											3,700,000
Transaction price											9,600,000
Adjustments to transaction price											9,600,000	14,700,000
Deferred revenue recognized under collaboration arrangement							$ 5,100,000				2,100,000	5,100,000
Upfront fee revenue, net of value added tax withholdings			$ 4,200,000
Clinical development milestone payments											1,700,000
Remaining transaction price											2,900,000
Remaining transaction price will be recorded in deferred revenue when invoiced											800,000
Zai Lab [Member] | China License and Collaboration Agreement [Member] | License Grant [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized											3,600,000	1,400,000	1,700,000
Zai Lab [Member] | China License and Collaboration Agreement [Member] | Companion Diagnostics Development [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized											1,900,000	$ 3,000,000	$ 3,300,000
Zai Lab [Member] | China License and Collaboration Agreement [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Receivables related to collaboration agreement											$ 10,000,000

License and Collaboration Arran

License and Collaboration Arrangements - Additional Information 2 (Detail) - USD ($) $ in Thousands	3 Months Ended							12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue								$ 4,516
Revenue recognized	$ 2,048	$ 3,424	$ 8,414	$ 3,210	$ 2,984	$ 3,333	$ 5,347	$ 13,178	$ 14,874	$ 49,868
Seagen, Inc [Member] | Seagen License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research collaboration and license agreement entered month and year								2020-02
Up-front fee								$ 5,000
Annual maintenance fees receivable								200
Transaction price								5,000
Transaction price recognized as collaboration revenue			$ 5,000
Seagen, Inc [Member] | Seagen License Agreement [Member] | Consulting Support
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized								$ 100

Acquired Technologies - Additio

Acquired Technologies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Research And Development Arrangement Contract To Perform For Others [Line Items]
License agreements expiration period	10 years
Galaxy Biotech, LLC [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payment	$ 0	$ 0	$ 9.5
Galaxy Biotech, LLC [Member] | Maximum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payables	77.4
BioWa, Inc. and Lonza Sales AG [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payment	0	$ 0	$ 0.9
BioWa, Inc. and Lonza Sales AG [Member] | Bemarituzumab Programs [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payment	$ 24.7

Other Income, Net - Schedule of

Other Income, Net - Schedule of Other Income, Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Income And Expenses [Abstract]
Interest income	$ 820	$ 4,740	$ 5,792
Sublease income	1,146
Other	(54)	(4)	(84)
Total	$ 1,912	$ 4,736	$ 5,708

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Current tax benefit
Federal	$ (6,630)
Total current tax benefit	(6,630)
Deferred tax expense
Total tax benefit	$ (6,630)

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax Expense (Benefit) Differs from Amount Computed by Applying Statutory Federal Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Abstract]
Federal statutory income tax	$ (19,102)	$ (28,812)	$ (29,495)
State statutory income tax	1	1	1
Stock compensation	1,966	4,055	3,698
Nontaxable equity premiums		(20)	(85)
Change in valuation allowance	17,754	32,540	38,953
Income from shareholder	3,513
Research and orphan drug credits	(4,701)	(8,015)	(13,192)
Tax benefit from alternative minimum tax credit refund	(6,630)
Other permanent items	569	$ 251	$ 120
Total tax benefit	$ (6,630)

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets Liabilities Net [Abstract]
Net operating loss carryforwards	$ 94,763	$ 85,928
Research and orphan drug credits	73,608	68,053
Deferred revenue	122	1,372
Stock-based compensation	5,390	7,562
Capitalized license and depreciation basis differences	2,906	3,196
Reserves, accruals and tenant improvement allowances	1,090	1,389
Operating lease liability	10,158	10,619
Total deferred tax assets	188,037	178,119
Less: valuation allowance	(182,319)	(168,691)
Net deferred tax assets	5,718	9,428
Capitalized license and depreciation basis differences	(808)	(2,374)
Operating right-of-use asset	(4,557)	(6,621)
Prepaid expenses	(353)	(433)
Total deferred tax liabilities	(5,718)	(9,428)
Total net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax [Line Items]
Increase (decrease) in valuation allowance	$ 13,600,000	$ 34,200,000
Net deferred tax assets, net of gross deferred tax liabilities	182,319,000	168,691,000
Reduction in tax attributes	1,400,000
Incurred interest and penalties	$ 0	$ 0
Ongoing tax examinations by tax authorities	We have no ongoing tax examinations by tax authorities at this time.
Federal tax authority [Member]
Income Tax [Line Items]
Operating loss carryforwards	$ 416,300,000
Operating losses carryforwards, Expiration date	Dec. 31, 2024
Federal tax authority [Member] | Research and Development and Orphan Drug [Member]
Income Tax [Line Items]
Tax credits available to offset future tax	$ 67,200,000
Tax credit carryforwards, Expiration date	Dec. 31, 2026
State tax authority [Member]
Income Tax [Line Items]
Operating loss carryforwards	$ 165,900,000
Operating losses carryforwards, Expiration date	Dec. 31, 2028
State tax authority [Member] | Research and Development and Orphan Drug [Member]
Income Tax [Line Items]
Tax credits available to offset future tax	$ 24,800,000

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Beginning Balance	$ 18,393	$ 16,660	$ 13,584
Additions for prior year tax positions	0	11	622
Additions for current year tax positions	1,020	1,722	2,454
Ending Balance	$ 19,413	$ 18,393	$ 16,660

Restructuring and Other Charg_3

Restructuring and Other Charges - Additional Information (Detail) $ in Thousands	Oct. 10, 2019Position	Jan. 31, 2019Employees	Dec. 31, 2020USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Restructuring Cost And Reserve [Line Items]
Number of company's workforce terminated	63	41
Percentage of company's workforce terminated		20.00%
Laboratory equipment [Member] | 2019 Restructure Plan [Member]
Restructuring Cost And Reserve [Line Items]
Estimated fair value			$ 3,900		$ 3,900
Impairment loss on long lived assets					1,900
Gain (loss) on disposition of assets					3,400
Employee-related [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges			$ 5,300	$ 1,900	$ 2,644	$ 4,528

Restructuring and Other Charg_4

Restructuring and Other Charges - Summary of Management's Expected and Actual Costs (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Restructuring Cost And Reserve [Line Items]
Total Estimated restructuring costs	$ 3,874
Total Restructuring cost incurred to date	3,874
Employee-related [Member]
Restructuring Cost And Reserve [Line Items]
Total Estimated restructuring costs	7,172
Total Restructuring cost incurred to date	7,172
Asset-related [Member]
Restructuring Cost And Reserve [Line Items]
Total Estimated restructuring costs	(3,298)
Total Restructuring cost incurred to date	$ (3,298)

Restructuring and Other Charg_5

Restructuring and Other Charges - Summary of Components of Restructuring Costs that are Recorded within Statement of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	$ (2,741)	$ 6,615
Employee-related [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	2,644	4,528
Asset-related [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	(5,385)	2,087
Research and development [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	(3,615)	6,213
Research and development [Member] | Employee-related [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	1,770	4,126
Research and development [Member] | Asset-related [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	(5,385)	2,087
General and administrative [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	874	402
General and administrative [Member] | Employee-related [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	$ 874	$ 402

Restructuring and Other Charg_6

Restructuring and Other Charges - Summary of Employee-related Activity In Accrued Personnel-related Expense Liability (Detail) - Employee-related [Member] - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Balance at beginning of year			$ 1,182
Charges	$ 5,300	$ 1,900	2,644	$ 4,528
Cash payments			$ (3,826)	(3,346)
Balance at end of year				$ 1,182

Subsequent Event - Additional I

Subsequent Event - Additional Information (Details) - USD ($) $ / shares in Units, $ in Billions	Mar. 04, 2021	Dec. 31, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Common stock, par value		$ 0.001	$ 0.001
Merger Agreement [Member] | Amgen, and Franklin Acquisition Sub, Inc. [Member]
Subsequent Event [Line Items]
Merger agreement entered date	Mar. 4, 2021
Common stock, par value	$ 0.001
Common stock, Price per share	$ 38
Equity value of common stock	$ 1.9

Selected Quarterly Financial _3

Selected Quarterly Financial Information - Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenue		$ 2,048	$ 3,424	$ 8,414	$ 3,210	$ 2,984	$ 3,333	$ 5,347	$ 13,178	$ 14,874	$ 49,868
Revenue	$ (708)
Net loss	$ (20,852)	$ (26,423)	$ (16,937)	$ (20,116)	$ (31,357)	$ (36,069)	$ (34,391)	$ (35,385)	$ (84,328)	$ (137,202)	$ (140,447)
Basic and diluted net loss per share	$ (0.51)	$ (0.74)	$ (0.48)	$ (0.57)	$ (0.89)	$ (1.03)	$ (0.99)	$ (1.02)	$ (2.29)	$ (3.92)	$ (4.13)