Five Prime Therapeutics (FPRX) 10-Q 3 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	FPRX
Entity Registrant Name	Five Prime Therapeutics, Inc.
Entity Central Index Key	0001175505
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
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 Quarterly Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		38,037,666

Balance Sheets (Unaudited)

Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 36,019	$ 55,800
Marketable securities	75,350	100,580
Receivables from collaborative partners	1,483	4,097
Income tax receivable	6,630
Prepaid and other current assets	3,793	6,243
Total current assets	123,275	166,720
Restricted cash	1,543	1,543
Property and equipment, net	11,691	22,534
Operating lease, right-of-use assets	19,854	30,934
Other long-term assets	4,018	2,411
Total assets	160,381	224,142
Current liabilities:
Accounts payable	396	1,184
Accrued personnel-related expenses	5,174	6,805
Other accrued liabilities	12,028	9,659
Operating lease obligations, current portion	4,198	4,080
Deferred revenue, current portion	1,251	1,296
Total current liabilities	23,047	23,024
Deferred revenue, long-term portion		5,113
Operating lease obligations, long-term portion	42,103	45,532
Stockholders' equity:
Common stock, $0.001 par value; 100,000,000 shares authorized, 36,589,525 issued and 35,620,167 outstanding at September 30, 2020; 36,280,368 issued and 35,219,791 outstanding at December 31, 2019.	36	35
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Additional paid-in capital	590,544	582,243
Accumulated other comprehensive income	10	78
Accumulated deficit	(495,359)	(431,883)
Total stockholders' equity	95,231	150,473
Total liabilities and stockholders' equity	$ 160,381	$ 224,142

Balance Sheets (Unaudited) (Par

Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 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	36,589,525	36,280,368
Common stock, shares outstanding	35,620,167	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 (Unaud

Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue:
Total revenue	$ 2,048	$ 2,984	$ 13,886	$ 11,664
Operating expenses:
Research and development	21,446	26,948	52,575	88,126
General and administrative	13,712	13,206	32,198	33,377
Total operating expenses	35,158	40,154	84,773	121,503
Loss from operations	(33,110)	(37,170)	(70,887)	(109,839)
Interest income	59	1,100	783	3,996
Other (expense) income, net	(2)	1	(2)	(2)
Loss before income tax	(33,053)	(36,069)	(70,106)	(105,845)
Income tax benefit	6,630		6,630
Net loss	$ (26,423)	$ (36,069)	$ (63,476)	$ (105,845)
Basic and diluted net loss per common share	$ (0.74)	$ (1.03)	$ (1.79)	$ (3.03)
Weighted-average shares used to compute basic and diluted net loss per common share	35,521	34,996	35,404	34,901
Collaboration revenue [Member]
Revenue:
Total revenue	$ 2,048	$ 2,984	$ 8,886	$ 11,664
License revenue [Member]
Revenue:
Total revenue			$ 5,000

Statements of Comprehensive Los

Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (26,423)	$ (36,069)	$ (63,476)	$ (105,845)
Other comprehensive (loss) gain:
Unrealized (loss) gain on marketable securities	(12)	(63)	(68)	185
Comprehensive loss	$ (26,435)	$ (36,132)	$ (63,544)	$ (105,660)

Statements of Stockholders' Equ

Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings (Accumulated Deficit) [Member]
Beginning Balance at Dec. 31, 2018	$ 265,139	$ 34	$ 559,892	$ (106)	$ (294,681)
Beginning Balance, Shares at Dec. 31, 2018		34,745,721
Issuance of common stock under equity incentive plans	222		222
Issuance of common stock under equity incentive plans, Shares		150,666
Repurchase of shares to satisfy tax withholding obligations	(670)		(670)
Repurchase of shares to satisfy tax withholding obligations, Shares		(57,703)
Stock-based compensation expense	4,872		4,872
Other comprehensive gain (loss)	148			148
Net loss	(35,385)				(35,385)
Ending Balance at Mar. 31, 2019	234,326	$ 34	564,316	42	(330,066)
Ending Balance, Shares at Mar. 31, 2019		34,838,684
Beginning Balance at Dec. 31, 2018	265,139	$ 34	559,892	(106)	(294,681)
Beginning Balance, Shares at Dec. 31, 2018		34,745,721
Net loss	(105,845)
Ending Balance at Sep. 30, 2019	178,434	$ 34	578,847	79	(400,526)
Ending Balance, Shares at Sep. 30, 2019		35,099,100
Beginning Balance at Mar. 31, 2019	234,326	$ 34	564,316	42	(330,066)
Beginning Balance, Shares at Mar. 31, 2019		34,838,684
Issuance of common stock under equity incentive plans	772		772
Issuance of common stock under equity incentive plans, Shares		131,586
Repurchase of shares to satisfy tax withholding obligations	(58)		(58)
Repurchase of shares to satisfy tax withholding obligations, Shares		(5,957)
Stock-based compensation expense	5,863		5,863
Other comprehensive gain (loss)	100			100
Net loss	(34,391)				(34,391)
Ending Balance at Jun. 30, 2019	206,612	$ 34	570,893	142	(364,457)
Ending Balance, Shares at Jun. 30, 2019		34,964,313
Issuance of common stock under equity incentive plans	4		4
Issuance of common stock under equity incentive plans, Shares		264,419
Repurchase of shares to satisfy tax withholding obligations	(706)		(706)
Repurchase of shares to satisfy tax withholding obligations, Shares		(129,632)
Stock-based compensation expense	8,656		8,656
Other comprehensive gain (loss)	(63)			(63)
Net loss	(36,069)				(36,069)
Ending Balance at Sep. 30, 2019	178,434	$ 34	578,847	79	(400,526)
Ending Balance, Shares at Sep. 30, 2019		35,099,100
Beginning Balance at Dec. 31, 2019	$ 150,473	$ 35	582,243	78	(431,883)
Beginning Balance, Shares at Dec. 31, 2019	35,219,791	35,219,791
Issuance of common stock under equity incentive plans, Shares		169,324
Repurchase of shares to satisfy tax withholding obligations	$ (277)		(277)
Repurchase of shares to satisfy tax withholding obligations, Shares		(65,059)
Stock-based compensation expense	4,482		4,482
Other comprehensive gain (loss)	(19)			(19)
Net loss	(20,116)				(20,116)
Ending Balance at Mar. 31, 2020	134,543	$ 35	586,448	59	(451,999)
Ending Balance, Shares at Mar. 31, 2020		35,324,056
Beginning Balance at Dec. 31, 2019	$ 150,473	$ 35	582,243	78	(431,883)
Beginning Balance, Shares at Dec. 31, 2019	35,219,791	35,219,791
Net loss	$ (63,476)
Ending Balance at Sep. 30, 2020	$ 95,231	$ 36	590,544	10	(495,359)
Ending Balance, Shares at Sep. 30, 2020	35,620,167	35,620,167
Beginning Balance at Mar. 31, 2020	$ 134,543	$ 35	586,448	59	(451,999)
Beginning Balance, Shares at Mar. 31, 2020		35,324,056
Issuance of common stock under equity incentive plans	299		299
Issuance of common stock under equity incentive plans, Shares		192,759
Repurchase of shares to satisfy tax withholding obligations	(103)		(103)
Repurchase of shares to satisfy tax withholding obligations, Shares		(35,591)
Stock-based compensation expense	2,179		2,179
Other comprehensive gain (loss)	(37)			(37)
Net loss	(16,937)				(16,937)
Ending Balance at Jun. 30, 2020	119,944	$ 35	588,823	22	(468,936)
Ending Balance, Shares at Jun. 30, 2020		35,481,224
Issuance of common stock under equity incentive plans	29		29
Issuance of common stock under equity incentive plans, Shares		202,182
Issuance of common stock under at-the-market equity offerings, shares		6,500
Repurchase of shares to satisfy tax withholding obligations	(368)	$ 1	(369)
Repurchase of shares to satisfy tax withholding obligations, Shares		(69,739)
Stock-based compensation expense	2,061		2,061
Other comprehensive gain (loss)	(12)			(12)
Net loss	(26,423)				(26,423)
Ending Balance at Sep. 30, 2020	$ 95,231	$ 36	$ 590,544	$ 10	$ (495,359)
Ending Balance, Shares at Sep. 30, 2020	35,620,167	35,620,167

Statements of Cash Flows (Unaud

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net loss	$ (63,476)	$ (105,845)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,701	3,850
Impairment of fixed assets	5,036
Impairment of ROU assets	8,792
Stock-based compensation expense	8,722	19,391
Amortization of discounts and premiums on marketable securities	(140)	(1,925)
Non-cash operating lease expense	1,894	1,739
Write-off of ROU assets	394
Gain on disposal of property and equipment	(3,617)
Changes in operating assets and liabilities:
Receivables from collaborative partners	2,614	1,432
Income tax receivable	(6,630)
Prepaid, other current assets and other long-term assets	812	5,413
Accounts payable	(759)	2,978
Accrued personnel-related expenses	(1,631)	(1,389)
Deferred revenue	(5,158)	(4,717)
Other accrued liabilities, and other long-term liabilities	2,369	(3,175)
Operating lease liabilities	(3,311)	(1,999)
Net cash used in operating activities	(51,388)	(84,247)
Investing activities
Purchases of marketable securities	(109,964)	(180,551)
Maturities of marketable securities	135,266	271,792
Proceeds from sales of property and equipment	6,737
Purchases of property and equipment	(44)	(1,578)
Net cash provided by investing activities	31,995	89,663
Financing activities
Proceeds from issuance of common stock under equity incentive plans	329	998
Proceeds from at-the-market equity offerings of common stock, net	32
Repurchase of shares to satisfy tax withholding obligations	(749)	(1,434)
Net cash used in financing activities	(388)	(436)
Net (decrease) increase in cash and cash equivalents and restricted cash	(19,781)	4,980
Cash, cash equivalents and restricted cash at beginning of period	57,343	45,496
Cash, cash equivalents and restricted cash at end of period	37,562	50,476
Supplemental disclosure
Property and equipment purchases included in accrued liabilities		29
Supplemental cash flow information
Cash and cash equivalents at beginning of period	55,800	43,953
Restricted cash at beginning of period	1,543	1,543
Cash, cash equivalents and restricted cash at beginning of period	57,343	45,496
Cash and cash equivalents at end of period	36,019	48,933
Restricted cash at end of period	1,543	1,543
Cash, cash equivalents and restricted cash at end of period	$ 37,562	$ 50,476

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Description of Business	1. Description of Business Five Prime Therapeutics, Inc. (we, us, our, or the company) is a clinical-stage biotechnology company focused on developing immune modulators and precision therapies to improve the lives of patients with solid tumor cancers Unaudited Interim Financial Information The accompanying financial information as of September 30, 2020 is unaudited. The financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of our financial condition at the date of the interim balance sheet. The accompanying unaudited financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2019, filed with the U.S. Securities and Exchange Commission, or the SEC, on February 27, 2020, or our Annual Report.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 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 GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes as of the date of the financial statements Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable. The COVID-19 pandemic may impact the development timelines for our clinical and preclinical programs. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of . As of the date of issuance of these financial statements, we are not aware of any specific event or circumstance that would require us to update our estimates, assumptions and judgments or revise the carrying value of our assets or liabilities. These estimates may change as new events occur and additional information is obtained and are recognized in the financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to our financial statements. Restricted Cash Restricted cash consists of a certificate of deposit held by our bank as collateral for a standby letter of credit in the same notional amount by our landlord to secure our obligations under our corporate office and laboratory facility lease that we entered into in December 2016. We are required to maintain this restricted cash balance, the amount of which is subject to reduction starting on January 1, 2023 if certain conditions are met, for the duration of this lease. 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. 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 September 30, 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 execution of a sublease agreement with Sutro Biopharma, Inc., or Sutro, pursuant to which we sublet to Sutro office and laboratory space at our current facilities. See Note 6 for additional information regarding this sublease. The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): September 30, 2020 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 18,818 $ 18,818 $ — $ — U.S. Treasury securities 47,350 47,350 — — Agency bonds 6,264 6,264 — — Commercial paper 23,986 — 23,986 — Certificate of deposit 1,543 — 1,543 — Total $ 97,961 $ 72,432 $ 25,529 $ — December 31, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets 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 $ — Revenue Recognition We determine revenue recognition for arrangements within the scope of Financial Accounting Standards Board, or FASB, Accounting Standard Update, ASU, 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. Net Loss Per Share of Common Stock We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since the effect of potentially dilutive securities is antidilutive. We excluded the following securities from the calculation of basic net loss per share (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Options to purchase common stock 5,005 3,706 4,587 3,868 Restricted stock awards (RSAs) 1,116 1,728 1,186 1,313 6,121 5,434 5,773 5,181 Impairment of Long-Lived Assets Long-lived assets, including property and equipment, 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 flow. In connection with the corporate restructuring we undertook in October 2019, or the October 2019 restructuring, we entered into a sublease agreement 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 lease cost for the term of the sublease exceeded the anticipated sublease income for that same period. We calculated the fair value of this asset group using discounted cash flows, which have significant unobservable inputs related to the discount rate and forecasts of future cash flows. We elected to exclude the operating lease obligations from the asset group when testing whether the carrying amount of the asset group is recoverable. As a result, we classified the fair value of this asset group within Level 3 of the fair value hierarchy. See Note 6 for additional information regarding this sublease. Restructuring and Other Charges We account for costs related to our 2019 corporate restructuring activities in accordance with ASC 420, Exit or Disposal Cost Obligations We 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 7 for additional information regarding charges related to our 2019 corporate restructurings. Accounting Pronouncements Adopted in 2020 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 August 2018, FASB issued ASU 2018-13, Fair Value Measurement–Disclosure Framework (Topic 820) , or ASU 2018-13. The updated guidance in ASU 2018-13 enhances the disclosure requirements on fair value measurements. We adopted ASU 2018-13 effective January 1, 2020. The adoption of ASU 2018-13 had no effect on our financial statements and disclosures . In June 2016, FASB issued ASU 2016-13, Financial Instruments–Credit Losses (Topic 326) In April 2015, FASB issued ASU 2018-15, Intangibles–Goodwill and Other–Internal-Use Software (Topic 350) Accounting Pronouncements Not Yet Adopted In December 2019, FASB issued ASU 2019-12, Income Taxes–Simplifying the Accounting for Income Taxes (Topic 740)

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	9 Months Ended
	Sep. 30, 2020
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	3. Cash Equivalents and Marketable Securities The following table summarizes our cash equivalents and marketable securities aggregated by investment category (in thousands): September 30, 2020 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 18,818 $ — $ — $ 18,818 U.S. Treasury securities 47,344 6 — 47,350 Agency bonds 6,262 2 — 6,264 Commercial paper 23,984 2 — 23,986 Total cash equivalents and marketable securities 96,408 10 — 96,418 Less: cash equivalents (21,068 ) — — (21,068 ) Total marketable securities $ 75,340 $ 10 $ — $ 75,350 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 There were no marketable securities in a continuous unrealized loss position for 12 months or less as of September 30, 2020 and December 31, 2019. There were no sales of available-for-sale securities in any of the periods presented. As such, no allowance for credit losses was necessary. As of September 30, 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 $ 75,340 $ 75,350 Total marketable securities $ 75,340 $ 75,350 We 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.

Equity Incentive Plans

Equity Incentive Plans	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plans	4. Equity Incentive Plans The following table summarizes option activity under our equity incentive plans and related information: Options Outstanding Weighted Weighted Average Average Remaining Number of Exercise Price Contractual Shares Per Share Term (years) Balance at December 31, 2019 3,314,722 $ 20.50 Options granted 2,000,502 4.37 Options exercised (32,925 ) 5.19 Options forfeited (218,564 ) 9.65 Options expired (80,107 ) 21.19 Balance at September 30, 2020 4,983,628 14.59 6.77 Options exercisable at September 30, 2020 2,986,279 20.14 5.17 We have granted restricted stock awards, or RSAs, some of which are subject to performance conditions and/or market conditions. RSAs are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting and are not forfeitable once fully vested. We base the fair value of RSAs on the closing sale price of our common stock on the grant date. For RSAs subject to market conditions, we based the fair value of the awards on a Monte Carlo simulation model. For RSAs subject to performance conditions, we recognize stock-based compensation expense using the accelerated attribution recognition method when it is probable that the performance condition will be achieved and, for RSAs subject to market conditions, we recognize stock-based compensation expense commencing at the grant date over the derived service period. The following table summarizes RSA activity under our 2013 Omnibus Incentive Plan and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at December 31, 2019 1,060,577 $ 11.24 RSAs granted 614,950 4.91 RSAs vested (478,007 ) 13.76 RSAs forfeited (228,162 ) 10.84 Unvested balance at September 30, 2020 969,358 6.08 As of September 30, 2020, there were 2,305,580 shares of common stock available for future issuance under our 2013 Omnibus Incentive Plan. Stock-Based Compensation Total stock-based compensation expense recognized was as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Research and development $ 958 $ 2,323 $ 2,633 $ 6,706 General and administrative 1,103 6,333 6,089 12,685 Total $ 2,061 $ 8,656 $ 8,722 $ 19,391 We estimated the fair value of stock options using the Black-Scholes option pricing model based on the date of grant of the applicable stock option with the following assumptions: Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Expected term (years) 6.0 5.3-6.0 5.0-6.3 5.5-6.3 Expected volatility 73.2% 67.0% 68.9%-73.2% 67.0%-67.7% Risk-free interest rate 0.4% 1.6%-1.7% 0.4%-1.3% 1.6%-2.5% Expected dividend yield 0% 0% 0% 0% As of September 30, 2020, we had $7.2 million of total unrecognized compensation expense related to unvested stock options that we expect to recognize over a weighted-average period of 2.9 years. Additionally, we had $2.7 million of total unrecognized compensation expense related to employee RSAs that we expect to recognize over a weighted-average period of 2.2 years. Stock Option Exchange Program On July 1, 2019, we commenced a tender offer to our employees, excluding 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 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 Omnibus Incentive 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 our 2013 Omnibus Incentive Plan. The exchange of stock options was treated as a modification for accounting purposes. The unamortized incremental expense remaining 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 $0.3 million as of September 30, 2020 over the remainder of the original requisite service period.

License and Collaboration Arran

License and Collaboration Arrangements	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Arrangements	5. License and Collaboration Arrangements The following tables present changes during the nine months ended September 30, 2020 in the balances of our contract assets, including receivables from collaboration partners, and contract liabilities, including deferred revenue (in thousands): Contract Assets Balance at December 31, 2019 $ 4,097 Additions 3,747 Deductions (6,361 ) Balance at September 30, 2020 $ 1,483 Contract Liabilities Balance at December 31, 2019 $ 6,409 Additions for advance billings 1,362 Deductions for performance obligations satisfied in current period (4,221 ) Deductions for updates to the measure of progress and decrease in transaction price from prior periods (2,299 ) Balance at September 30, 2020 $ 1,251 Bristol-Myers Squibb Company Immuno-Oncology Research Collaboration In March 2014, we entered into a research collaboration and license agreement, or the immuno-oncology research collaboration, with Bristol-Myers Squibb Company, or BMS. We identified one performance obligation under the immuno-oncology research collaboration 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 non-refundable upfront fee, $13.7 million of research funding and $2.4 million of equity premium. as uncertain events are resolved and other changes in circumstances occur For the three and nine months ended September 30, 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 obligation was $0 for each of the three months ended September 30, 2020 and 2019, and $0 and $1.4 million for the nine months ended September 30, 2020 and 2019, respectively. L icense and Collaboration Agreement On October 14, 2015, we entered into a license and collaboration agreement, or the cabiralizumab collaboration agreement, with BMS. The cabiralizumab collaboration agreement supersedes the clinical trial collaboration agreement we entered into with BMS in November 2014, or the original collaboration agreement. We assessed the two agreements separately as standalone agreements under Topic 606. Under the original collaboration agreement, we identified one performance obligation for the execution of 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 clinical research organization, or 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 and $0.9 million of the transaction price as revenue for the three months ended September 30, 2020 and 2019, respectively, and $0.8 million and $3.8 million for the nine months ended September 30, 2020 and 2019, respectively. Total revenue recognized for reimbursements for the three months ended September 30, 2020 and 2019 was $0 and $0.7 million, respectively, and for the nine months ended September 30, 2020 and 2019 was $1.7 million and $3.1 million, respectively. Under the cabiralizumab collaboration agreement, we identified the following performance obligations: (1) the license grant to BMS and (2) the transfer of licensed know-how to BMS. The transaction price consisted of the $350.0 million non-refundable up-front fee. As t was fully recognized as revenue concurrent with the transfer of the license and know-how in prior years We concluded that the transaction price should not yet include milestone payments that may become due, as they are fully constrained. 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 three and nine months ended September 30, 2020, no adjustments were made to the transaction price. Zai Lab (Shanghai) Co., Ltd. In December 2017, we entered into a license and collaboration agreement, or the China collaboration agreement, with Zai Lab (Shanghai) Co., Ltd., or Zai Lab, pursuant to which we granted Zai Lab an exclusive license to develop and commercialize bemarituzumab in China, Hong Kong, Macau and Taiwan. We are currently dosing patients in a global double-blind Phase 2 clinical trial of bemarituzumab in combination with mFOLFOX6 as front-line treatment of patients with advanced FGFR2b+/HER2- gastric or GEJ cancer, which we refer to as our FIGHT trial . We identified the following performance obligations under the China collaboration agreement: (1) the 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) the 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. The transaction price of $9.6 million consists of the $3.7 million of expected reimbursement from Zai Lab for global development activities, $4.2 million non-refundable upfront fee and $1.7 million clinical development milestone payment. We have not included the regulatory milestone payments in the transaction price, as all such milestone amounts are fully constrained. 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 t We will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. During the three and nine months ended September 30, 2020, the transaction price increased to $9.6 million from $8.9 million and was reduced to $9.6 million from $14.7 million, respectively, primarily as a result of our decision to amend 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. We will recognize revenue from reimbursements for the development of companion diagnostics when we have the right to invoice Zai Lab. Revenue recognized for the license grant performance obligation was $1.9 million and $0.4 million for the three months ended September 30, 2020 and 2019, respectively, and $5.2 million and $1.0 million for the nine months ended September 30, 2020 and 2019, respectively. Total revenue recognized for the companion diagnostics development performance obligation was $0.2 million and $1.0 million for the three months ended September 30, 2020 and 2019, respectively, and $1.1 million and $2.4 million for the nine months ended September 30, 2020 and 2019, respectively. Of the remaining transaction price of $1.3 million, we recorded $0.6 million in deferred revenue, which we will recognize over the estimated performance period for satisfaction of the performance obligations. The remaining $0.7 million of the transaction price will be recorded in deferred revenue when invoiced as we complete global development activities. Seagen Inc. In February 2020, we entered into a global 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. Pursuant to the Seagen license agreement, Seagen paid us an upfront fee of $5.0 million. Additionally, 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 an additional 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. Unless earlier terminated by either party, the Seagen agreement will expire on a licensed product-by-licensed product and country-by-country basis upon the expiration of Seagen’s royalty term with respect to each licensed product in the applicable country under the agreement. Seagen may terminate the agreement in its entirety at any time with advance written notice. Either party may terminate the agreement in its entirety with written notice for the other party’s material breach if such other party fails to cure the breach. . We may terminate the agreement in its entirety if Seagen or its affiliates or sublicensees commences a legal action challenging the validity, enforceability or scope of any of our patents. Either party also may terminate the agreement in its entirety upon certain insolvency events involving the other party. Under the Seagen license agreement, we identified one performance obligation for the license grant. The transaction price consists of the $5.0 million non-refundable upfront fee. As t transaction price of $5.0 million was fully recognized. For the three and nine months ended September 30, 2020, no milestone payments were triggered under the Seagen license agreement. 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 for the in each reporting period as uncertain events are resolved and other changes in circumstances occur.

Leases

Leases	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	6. Leases We adopted ASU 2016-02, Leases (Topic 842) etain the lease classification and initial direct costs for any leases that exist prior to adoption of the In addition, we elected the accounting policy of not recording short-term leases with a lease term at the commencement date of twelve months or less on the balance sheet as permitted by the new standard. 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 have evaluated our leases and determined that, effective upon the adoption of ASU 2016-02, they were all operating leases. The classification of our leases is consistent with our determination under the previous accounting standard. The balance sheet classification of our lease assets and liabilities is presented on our balance sheet. We entered into a lease agreement for our corporate office and laboratory facility in December 2016, which we refer to as the facility lease. We moved into this corporate office and laboratory facility in December 2017. The facility lease has an initial term of 10 years, beginning on the rent commencement date, with an option to extend the lease for an additional period of five years. We did not have to pay rent until the rent commencement date of January 1, 2018, and rent was reduced by 50% for the first six months. The facility lease contains scheduled rent increases over the lease term. We received lease incentives from our landlord for a portion of the costs of leasehold improvements we made to the premises. In addition, the 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 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. The discount rate of our facility lease is 7%, and the remaining lease term of our facility lease is seven years as of September 30, 2020. 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. The instruments lease has two three-year 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 of office and laboratory space that we currently lease at 111 Oyster Point Boulevard, South San Francisco, California, or the premises. The facility sublease is subordinate to the 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 facility lease. We determined that the facility sublease is an operating lease, which is consistent with the classification of the underlying facility lease. Under the facility sublease, we will sublet three of the four floors of the premises, or the initial premises, with Sutro’s obligation to pay rent beginning on the rent commencement date of July 2, 2021, or the initial premises commencement date, for the initial premises. 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 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. We will recognize sublease income on a straight-line basis beginning in the fourth quarter of 2020. Variable sublease payments under the facility sublease will be recognized when the corresponding variable lease payments under the facility lease are incurred. With the execution of the facility sublease , in which the lease cost for the term of the facility sublease exceed s the anticipated sublease income for that same period, we tested the operating lease right-of-use asset s and related leasehold improvements and furniture and fixtures for impairment as of September 1, 2020 . We recorded a n 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 p remises, 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. The impairment loss adjusted all of the carrying values of the operating lease right-of-use asset s to $ 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. Prior to September 1, 2020, the single lease cost was calculated so that the cost of the lease was allocated over the lease term on a straight-line basis. As of September 1, 2020, the cost of the lease is no longer recognized on a straight-line basis due to variability in the interest amortization . Variable lease payments that are not included in the lease liability are recognized on the statement of operations in the period in which the obligation for those payments is incurred. In addition, we continue to amortize the leasehold improvements and depreciate furniture and fixtures, each at their revised carrying values, over their remaining useful lives as those lives do not extend beyond the sublease term. The operating lease obligations did not change since we were not relieved of the primary obligation under the facility lease . For each of the three months ended September 30, 2020 and 2019, we recognized operating lease cost of $1.5 million, Minimum lease payments The table below presents the undiscounted cash flows for each of the first five years of the lease term and the total of the remaining years of the lease term. For the facility lease, the undiscounted cash flows are reconciled to the operating lease liabilities recorded on the balance sheet (in thousands): Facility Lease Facility Sublease Remainder of 2020 $ 1,819 $ — Years ending December 31, 2021 7,524 2,547 2022 7,787 — 2023 8,064 6,310 2024 8,341 7,476 2025 and beyond 26,825 24,034 Total minimum lease payments $ 60,360 $ 40,367 Less: amount of lease payments representing interest (14,059 ) Present value of future minimum lease payments $ 46,301 Less: operating lease obligations, current portion (4,198 ) Operating lease obligations, long-term portion $ 42,103 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.

Restructuring and Other Charges

Restructuring and Other Charges	9 Months Ended
	Sep. 30, 2020
Restructuring And Related Activities [Abstract]
Restructuring and Other Charges	7. 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 our 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 amounted to approximately $1.8 million for severance and other benefit costs related to the restructuring. 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. We expect the October restructuring to be completed by the end of 2020. Asset Impairment Charge In conjunction with our 2019 corporate restructurings, we evaluated the lab equipment we owned and determined that the carrying value was no longer recoverable. An impairment loss of $1.9 million was recorded in our research and development costs within our statement of operations, primarily during the fourth quarter of 2019. We reclassified the lab 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 lab equipment through an auction conducted by a third-party vendor recorded a gain of $0 and $3.4 million for the proceeds of such auction against . The following table summarizes management’s estimates of costs that are expected to be incurred that are probable and can be estimated as of September 30, 2020 and the actual costs incurred through September 30, 2020 in connection with our 2019 corporate restructurings (in thousands): Total Estimated Restructuring Total Restructuring Cost Incurred Costs To Date Employee retention, severance and termination benefits $ 7,172 $ 6,663 Asset impairments and other costs, net gains on sale (3,298 ) (3,298 ) $ 3,874 $ 3,365 The following table presents the components of restructuring and other related costs for the three and nine months ended September 30, 2020 and their location within our income statement (in thousands): For the Three Months Ended For the Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Research and development $ 306 $ — $ (3,711 ) $ 1,893 General and administrative 209 — 460 — Total $ 515 $ — $ (3,251 ) $ 1,893 The following table presents the activity in the accrued personnel-related expense liability associated with the 2019 corporate restructurings for the nine months ended September 30, 2020 (in thousands): Total Severance and Retention Costs Accrued balance as of December 31, 2019 $ 1,183 Charges 2,134 Cash payments (1,646 ) Accrued balance as of September 30, 2020 $ 1,671

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	8. Subsequent Events On August 6, 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 . As of November 2, 2020, we have raised approximately $7.4 million in net proceeds, primarily during the fourth quarter of 2020. In October 2020, we entered into an agreement to rent laboratory space. The term of this agreement began on November 1, 2020. This agreement has an initial term of two months and will renew automatically for subsequent two-month

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes as of the date of the financial statements Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable. The COVID-19 pandemic may impact the development timelines for our clinical and preclinical programs. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of . As of the date of issuance of these financial statements, we are not aware of any specific event or circumstance that would require us to update our estimates, assumptions and judgments or revise the carrying value of our assets or liabilities. These estimates may change as new events occur and additional information is obtained and are recognized in the financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to our financial statements.
Restricted Cash	Restricted Cash Restricted cash consists of a certificate of deposit held by our bank as collateral for a standby letter of credit in the same notional amount by our landlord to secure our obligations under our corporate office and laboratory facility lease that we entered into in December 2016. We are required to maintain this restricted cash balance, the amount of which is subject to reduction starting on January 1, 2023 if certain conditions are met, for the duration of this lease.
Fair Value Measurements	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. 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 September 30, 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 execution of a sublease agreement with Sutro Biopharma, Inc., or Sutro, pursuant to which we sublet to Sutro office and laboratory space at our current facilities. See Note 6 for additional information regarding this sublease. The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): September 30, 2020 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 18,818 $ 18,818 $ — $ — U.S. Treasury securities 47,350 47,350 — — Agency bonds 6,264 6,264 — — Commercial paper 23,986 — 23,986 — Certificate of deposit 1,543 — 1,543 — Total $ 97,961 $ 72,432 $ 25,529 $ — December 31, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets 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 $ —
Revenue Recognition	Revenue Recognition We determine revenue recognition for arrangements within the scope of Financial Accounting Standards Board, or FASB, Accounting Standard Update, ASU, 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.
Net Loss Per Share of Common Stock	Net Loss Per Share of Common Stock We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since the effect of potentially dilutive securities is antidilutive. We excluded the following securities from the calculation of basic net loss per share (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Options to purchase common stock 5,005 3,706 4,587 3,868 Restricted stock awards (RSAs) 1,116 1,728 1,186 1,313 6,121 5,434 5,773 5,181
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets, including property and equipment, 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 flow. In connection with the corporate restructuring we undertook in October 2019, or the October 2019 restructuring, we entered into a sublease agreement 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 lease cost for the term of the sublease exceeded the anticipated sublease income for that same period. We calculated the fair value of this asset group using discounted cash flows, which have significant unobservable inputs related to the discount rate and forecasts of future cash flows. We elected to exclude the operating lease obligations from the asset group when testing whether the carrying amount of the asset group is recoverable. As a result, we classified the fair value of this asset group within Level 3 of the fair value hierarchy. See Note 6 for additional information regarding this sublease.
Restructuring and Other Charges	Restructuring and Other Charges We account for costs related to our 2019 corporate restructuring activities in accordance with ASC 420, Exit or Disposal Cost Obligations We 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 7 for additional information regarding charges related to our 2019 corporate restructurings.
Accounting Pronouncements Adopted in 2020	Accounting Pronouncements Adopted in 2020 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 August 2018, FASB issued ASU 2018-13, Fair Value Measurement–Disclosure Framework (Topic 820) , or ASU 2018-13. The updated guidance in ASU 2018-13 enhances the disclosure requirements on fair value measurements. We adopted ASU 2018-13 effective January 1, 2020. The adoption of ASU 2018-13 had no effect on our financial statements and disclosures . In June 2016, FASB issued ASU 2016-13, Financial Instruments–Credit Losses (Topic 326) In April 2015, FASB issued ASU 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 2019-12, Income Taxes–Simplifying the Accounting for Income Taxes (Topic 740)

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Financial Instruments Measured at Fair Value	The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): September 30, 2020 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 18,818 $ 18,818 $ — $ — U.S. Treasury securities 47,350 47,350 — — Agency bonds 6,264 6,264 — — Commercial paper 23,986 — 23,986 — Certificate of deposit 1,543 — 1,543 — Total $ 97,961 $ 72,432 $ 25,529 $ — December 31, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets 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 $ —
Securities Excluded from Calculation of Basic Net Loss Per Share	We excluded the following securities from the calculation of basic net loss per share (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Options to purchase common stock 5,005 3,706 4,587 3,868 Restricted stock awards (RSAs) 1,116 1,728 1,186 1,313 6,121 5,434 5,773 5,181

Cash Equivalents and Marketab_2

Cash Equivalents and Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2020
Cash And Cash Equivalents [Abstract]
Summary of Cash Equivalents and Marketable Securities Aggregated by Investment Category	The following table summarizes our cash equivalents and marketable securities aggregated by investment category (in thousands): September 30, 2020 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 18,818 $ — $ — $ 18,818 U.S. Treasury securities 47,344 6 — 47,350 Agency bonds 6,262 2 — 6,264 Commercial paper 23,984 2 — 23,986 Total cash equivalents and marketable securities 96,408 10 — 96,418 Less: cash equivalents (21,068 ) — — (21,068 ) Total marketable securities $ 75,340 $ 10 $ — $ 75,350 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
Summary of Marketable Securities in Continuous Unrealized Loss Position
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	As of September 30, 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 $ 75,340 $ 75,350 Total marketable securities $ 75,340 $ 75,350

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Option Activity under Equity Incentive Plans and Related Information	The following table summarizes option activity under our equity incentive plans and related information: Options Outstanding Weighted Weighted Average Average Remaining Number of Exercise Price Contractual Shares Per Share Term (years) Balance at December 31, 2019 3,314,722 $ 20.50 Options granted 2,000,502 4.37 Options exercised (32,925 ) 5.19 Options forfeited (218,564 ) 9.65 Options expired (80,107 ) 21.19 Balance at September 30, 2020 4,983,628 14.59 6.77 Options exercisable at September 30, 2020 2,986,279 20.14 5.17
Schedule of Restricted Stock Award Activity under 2013 Omnibus Incentive Plan and Related Information	The following table summarizes RSA activity under our 2013 Omnibus Incentive Plan and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at December 31, 2019 1,060,577 $ 11.24 RSAs granted 614,950 4.91 RSAs vested (478,007 ) 13.76 RSAs forfeited (228,162 ) 10.84 Unvested balance at September 30, 2020 969,358 6.08
Schedule of Stock-Based Compensation Expenses Recognized	Total stock-based compensation expense recognized was as follows (in thousands) Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Research and development $ 958 $ 2,323 $ 2,633 $ 6,706 General and administrative 1,103 6,333 6,089 12,685 Total $ 2,061 $ 8,656 $ 8,722 $ 19,391
Schedule of Stock Options Weighted-Average Assumptions	We estimated the fair value of stock options using the Black-Scholes option pricing model based on the date of grant of the applicable stock option with the following assumptions: Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Expected term (years) 6.0 5.3-6.0 5.0-6.3 5.5-6.3 Expected volatility 73.2% 67.0% 68.9%-73.2% 67.0%-67.7% Risk-free interest rate 0.4% 1.6%-1.7% 0.4%-1.3% 1.6%-2.5% Expected dividend yield 0% 0% 0% 0%

License and Collaboration Arr_2

License and Collaboration Arrangements (Tables)	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Changes in Balances of Contract Assets and Contract Liabilities	The following tables present changes during the nine months ended September 30, 2020 in the balances of our contract assets, including receivables from collaboration partners, and contract liabilities, including deferred revenue (in thousands): Contract Assets Balance at December 31, 2019 $ 4,097 Additions 3,747 Deductions (6,361 ) Balance at September 30, 2020 $ 1,483 Contract Liabilities Balance at December 31, 2019 $ 6,409 Additions for advance billings 1,362 Deductions for performance obligations satisfied in current period (4,221 ) Deductions for updates to the measure of progress and decrease in transaction price from prior periods (2,299 ) Balance at September 30, 2020 $ 1,251

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2020
Operating Lease Liabilities Payments Due [Abstract]
Summary of Undiscounted Cash Flows to Operating Lease Liabilities	The table below presents the undiscounted cash flows for each of the first five years of the lease term and the total of the remaining years of the lease term. For the facility lease, the undiscounted cash flows are reconciled to the operating lease liabilities recorded on the balance sheet (in thousands): Facility Lease Facility Sublease Remainder of 2020 $ 1,819 $ — Years ending December 31, 2021 7,524 2,547 2022 7,787 — 2023 8,064 6,310 2024 8,341 7,476 2025 and beyond 26,825 24,034 Total minimum lease payments $ 60,360 $ 40,367 Less: amount of lease payments representing interest (14,059 ) Present value of future minimum lease payments $ 46,301 Less: operating lease obligations, current portion (4,198 ) Operating lease obligations, long-term portion $ 42,103

Restructuring and Other Charg_2

Restructuring and Other Charges (Tables)	9 Months Ended
	Sep. 30, 2020
Restructuring And Related Activities [Abstract]
Summary of Management's Expected and Actual Costs	The following table summarizes management’s estimates of costs that are expected to be incurred that are probable and can be estimated as of September 30, 2020 and the actual costs incurred through September 30, 2020 in connection with our 2019 corporate restructurings (in thousands): Total Estimated Restructuring Total Restructuring Cost Incurred Costs To Date Employee retention, severance and termination benefits $ 7,172 $ 6,663 Asset impairments and other costs, net gains on sale (3,298 ) (3,298 ) $ 3,874 $ 3,365
Summary of Components of Restructuring and Other Related Costs and their Location within Income Statement	The following table presents the components of restructuring and other related costs for the three and nine months ended September 30, 2020 and their location within our income statement (in thousands): For the Three Months Ended For the Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Research and development $ 306 $ — $ (3,711 ) $ 1,893 General and administrative 209 — 460 — Total $ 515 $ — $ (3,251 ) $ 1,893
Summary of Accrued Personnel-related Expense Liability Associated with Restructuring	The following table presents the activity in the accrued personnel-related expense liability associated with the 2019 corporate restructurings for the nine months ended September 30, 2020 (in thousands): Total Severance and Retention Costs Accrued balance as of December 31, 2019 $ 1,183 Charges 2,134 Cash payments (1,646 ) Accrued balance as of September 30, 2020 $ 1,671

Description of Business - Addit

Description of Business - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2020Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Summary of Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets
Total	$ 97,961	$ 128,576
Money market funds [Member]
Assets
Cash equivalents	18,818	21,706
Agency Bonds [Member]
Assets
Cash equivalents	6,264	48,834
Commercial paper [Member]
Assets
Cash equivalents	23,986	19,195
Certificate of deposit [Member]
Assets
Cash equivalents	1,543	1,543
Corporate bonds [Member]
Assets
Cash equivalents		1,800
Level 1 [Member]
Assets
Total	72,432	106,038
Level 1 [Member] | Money market funds [Member]
Assets
Cash equivalents	18,818	21,706
Level 1 [Member] | Agency Bonds [Member]
Assets
Cash equivalents	6,264	48,834
Level 2 [Member]
Assets
Total	25,529	22,538
Level 2 [Member] | Commercial paper [Member]
Assets
Cash equivalents	23,986	19,195
Level 2 [Member] | Certificate of deposit [Member]
Assets
Cash equivalents	1,543	1,543
Level 2 [Member] | Corporate bonds [Member]
Assets
Cash equivalents		1,800
U.S. Treasury securities [Member]
Assets
U.S. Treasury securities	47,350	35,498
U.S. Treasury securities [Member] | Level 1 [Member]
Assets
U.S. Treasury securities	$ 47,350	$ 35,498

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Securities Excluded from Calculation of Basic Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	6,121	5,434	5,773	5,181
Options to purchase common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	5,005	3,706	4,587	3,868
Restricted stock awards (RSAs) [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	1,116	1,728	1,186	1,313

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2019
2019 Restructure Plan [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Sublease Agreement With Sutro Entered Month And Year.	2020-09

Cash Equivalents and Marketab_3

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities Aggregated by Investment Category (Detail) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 75,340,000	$ 100,502,000
Unrealized Gains	10,000	78,000
Unrealized Losses	0	0
Estimated Fair Value	75,350,000	100,580,000
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	18,818,000	21,706,000
Estimated Fair Value	18,818,000	21,706,000
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	47,344,000	35,471,000
Unrealized Gains	6,000	27,000
Estimated Fair Value	47,350,000	35,498,000
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	6,262,000	48,790,000
Unrealized Gains	2,000	44,000
Estimated Fair Value	6,264,000	48,834,000
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	23,984,000	19,188,000
Unrealized Gains	2,000	7,000
Estimated Fair Value	23,986,000	19,195,000
Total cash equivalents and marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	96,408,000	126,955,000
Unrealized Gains	10,000	78,000
Estimated Fair Value	96,418,000	127,033,000
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		1,800,000
Estimated Fair Value		1,800,000
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	(21,068,000)	(26,453,000)
Estimated Fair Value	$ (21,068,000)	$ (26,453,000)

Cash Equivalents and Marketab_4

Cash Equivalents and Marketable Securities - Additional Information (Detail) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Marketable securities, unrealized loss	$ 0	$ 0

Cash Equivalents and Marketab_5

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	Sep. 30, 2020	Dec. 31, 2019
Available For Sale Securities Debt Maturities [Abstract]
Amortized Cost, In one year or less	$ 75,340
Amortized Cost Basis	75,340	$ 100,502
Estimated Fair Value, In one year or less	75,350
Total marketable securities, Estimated Fair Value	$ 75,350	$ 100,580

Equity Incentive Plans - Schedu

Equity Incentive Plans - Schedule of Option Activity under Equity Incentive Plans and Related Information (Detail)	9 Months Ended
	Sep. 30, 2020$ / 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	(32,925)
Number of Shares, Options forfeited | shares	(218,564)
Number of Shares, Options expired | shares	(80,107)
Number of Shares, Ending balance | shares	4,983,628
Number of Shares, Options exercisable | shares	2,986,279
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	5.19
Weighted-Average Exercise Price Per Share, Options forfeited | $ / shares	9.65
Weighted-Average Exercise Price Per Share, Options expired | $ / shares	21.19
Weighted-Average Exercise Price Per Share, Options ending balance | $ / shares	14.59
Weighted-Average Exercise Price Per Share, Options exercisable | $ / shares	$ 20.14
Weighted-Average Remaining Contractual Terms, Options ending balance	6 years 9 months 7 days
Weighted-Average Remaining Contractual Term, Options exercisable	5 years 2 months 1 day

Equity Incentive Plans - Sche_2

Equity Incentive Plans - Schedule of Restricted Stock Award Activity under 2013 Omnibus Incentive Plan and Related Information (Detail) - Restricted Stock Awards [Member]	9 Months Ended
	Sep. 30, 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	(478,007)
Number of Shares, Forfeited | shares	(228,162)
Number of Shares, Unvested, Ending balance | shares	969,358
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	13.76
Weighted-Average Grant-Date Fair Value, Forfeited | $ / shares	10.84
Weighted-Average Grant-Date Fair Value, Unvested, Ending balance | $ / shares	$ 6.08

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Detail) $ / shares in Units, $ in Millions	Jul. 29, 2019Employee$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Jul. 01, 2019$ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation expense related to unvested stock options | $		$ 7.2
Unrecognized compensation expense expected to recognize, weighted-average period		2 years 10 months 24 days
Exercise price per share, new options granted | $ / shares		$ 4.37
Employee [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 2 months 12 days
Total unrecognized compensation expense related to employee RSAs | $		$ 2.7
2013 Omnibus Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for future issuance	201,229	2,305,580
Stock option exchange offer, maximum term	7 years
Stock Option Exchange Program [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option exchange program, description		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 | $		$ 0.3

Equity Incentive Plans - Sche_3

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 2,061	$ 8,656	$ 8,722	$ 19,391
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	958	2,323	2,633	6,706
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 1,103	$ 6,333	$ 6,089	$ 12,685

Equity Incentive Plans - Sche_4

Equity Incentive Plans - Schedule of Stock Options Assumptions (Detail) - Options [Member]	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	73.20%	67.00%
Risk-free interest rate	0.40%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years	5 years 3 months 18 days	5 years	5 years 6 months
Expected volatility			68.90%	67.00%
Risk-free interest rate		1.60%	0.40%	1.60%
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		6 years	6 years 3 months 18 days	6 years 3 months 18 days
Expected volatility			73.20%	67.70%
Risk-free interest rate		1.70%	1.30%	2.50%

License and Collaboration Arr_3

License and Collaboration Arrangements - Summary of Changes in Balances of Contract Assets and Contract Liabilities (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Contract With Customer Asset And Liability [Abstract]
Beginning balance	$ 4,097
Additions	3,747
Deductions	(6,361)
Ending balance	1,483
Beginning balance	6,409
Additions for advance billings	1,362
Deductions for performance obligations satisfied in current period	(4,221)
Deductions for updates to the measure of progress and decrease in transaction price from prior periods	(2,299)
Ending balance	$ 1,251

License and Collaboration Arr_4

License and Collaboration Arrangements - Additional Information (Detail) - USD ($)	Oct. 14, 2015	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2015	Jun. 30, 2020	Mar. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue				$ 4,221,000
Bristol-Myers Squibb Company [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable up-front fee	$ 30,000,000
Bristol-Myers Squibb Company [Member] | Immuno-Oncology Collaboration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research collaboration and license agreement entered month and year				2014-03
Transaction price				$ 36,100,000
Non-refundable up-front fee				20,000,000
Equity premium				2,400,000
Milestone payment		$ 0		0
Adjustments to transaction price		0		0
Research funding received				13,700,000
Bristol-Myers Squibb Company [Member] | Immuno-Oncology Collaboration [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue								$ 36,100,000
Bristol-Myers Squibb Company [Member] | Immuno-Oncology Collaboration [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | ASU 2014-09 [Member] | Actual Costs Incurred as a Percentage of Total Budgeted Costs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized		0	$ 0	0	$ 1,400,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable up-front fee				350,000,000
Milestone payment		0		0
Adjustments to transaction price		0		$ 0
Revenue recognized							$ 30,000,000
License and collaboration agreement entered date				Oct. 14, 2015
Recognized revenue under collaboration arrangement						$ 350,000,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized		0	700,000	$ 1,700,000	3,100,000
Bristol-Myers Squibb Company [Member] | Cabiralizumab Collaboration Agreement [Member] | ASU 2014-09 [Member] | Actual Costs Incurred as a Percentage of Total Budgeted Costs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized		0	900,000	800,000	3,800,000
Zai Lab [Member] | China License and Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable up-front fee				4,200,000
Milestone payment		0		0
Adjustments to transaction price		14,700,000		9,600,000
Revenue recognized		200,000	1,000,000	$ 1,100,000	2,400,000
License and collaboration agreement entered month and year				2017-12
Collaboration and license agreements transaction price				$ 9,600,000
Expected reimbursements		3,700,000		3,700,000
Receivables related to collaboration agreement		1,700,000		1,700,000
Adjustments to transaction price increased		8,900,000		9,600,000
Remaining transaction price		1,300,000		1,300,000
Remaining transaction price recorded in deferred revenue		600,000		600,000
Remaining transaction price will be recorded in deferred revenue when invoiced		700,000		700,000
Zai Lab [Member] | China License and Collaboration Agreement [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized		$ 1,900,000	$ 400,000	$ 5,200,000	$ 1,000,000

License and Collaboration Arr_5

License and Collaboration Arrangements - Additional Information 2 (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue			$ 4,221,000
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
Received upfront payment			$ 5,000,000
Annual maintenance fees receivable			200,000
Transaction price		$ 5,000,000
Transaction price recognized as collaboration revenue		$ 5,000,000
Milestone payment	$ 0		0
Seagen, Inc [Member] | Seagen License Agreement [Member] | Consulting Support [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from contracts with customers	0		0
Seagen, Inc [Member] | Seagen License Agreement [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sales based contingent payments receivable			162,500,000
Seagen, Inc [Member] | Seagen License Agreement [Member] | Maximum [Member] | First Licensed Product [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Specified development and regulatory milestone payments	132,000,000		132,000,000
Seagen, Inc [Member] | Seagen License Agreement [Member] | Maximum [Member] | Second Licensed Product [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Specified development and regulatory milestone payments	68,000,000		68,000,000
Seagen, Inc [Member] | Seagen License Agreement [Member] | Maximum [Member] | Each Subsequent Licensed Products [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Specified development and regulatory milestone payments	$ 19,000,000		$ 19,000,000

Leases - Additional Information

Leases - Additional Information (Detail)	Jan. 01, 2019USD ($)	Jul. 31, 2018InstrumentTerm	Sep. 30, 2020USD ($)ft²Floor	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)ft²Floor	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Lessee Lease Description [Line Items]
Lease term			10 years		10 years
Lease option additional extend term			5 years		5 years
Rent commencement date					Jan. 1, 2018
Percentage of rent reduction in first six months					50.00%
Additional lease requirements					In addition, the 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 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.
Discount rate of facility lease			7.00%		7.00%
Remaining facility lease term			7 years		7 years
Research and development costs			$ 21,446,000	$ 26,948,000	$ 52,575,000	$ 88,126,000
General and administrative costs			13,712,000	13,206,000	32,198,000	33,377,000
Operating lease, right-of-use assets			19,854,000		19,854,000		$ 30,934,000
Operating lease cost			1,500,000	1,500,000	4,900,000	4,600,000
Variable lease cost			500,000	400,000	1,900,000	1,300,000
Cash paid for operating lease liabilities			$ 2,200,000	$ 1,900,000	$ 6,000,000	$ 4,900,000
Facility sublease expansion commencement assumption term					24 months
Sub Lease Agreement with Sutro [Member]
Lessee Lease Description [Line Items]
Office and laboratory space (in square feet) | ft²			115,466		115,466
Facility Sublease [Member]
Lessee Lease Description [Line Items]
Lease term			6 years 6 months		6 years 6 months
Number of floors in the premises | Floor			4		4
Number of floors sublet | Floor			3		3
Rent commencement date					Jul. 2, 2021
Impairment loss					$ 13,800,000
Research and development costs					7,300,000
General and administrative costs					6,500,000
Operating lease, right-of-use assets			$ 20,100,000		20,100,000
Impairment loss adjusted the carrying values of leasehold improvements			11,200,000		11,200,000
Impairment loss adjusted the carrying values of furniture and fixtures			300,000		300,000
Bemarituzumab Programs [Member]
Lessee Lease Description [Line Items]
Lease term		3 years
Number of sequencing instruments | Instrument		4
Number of terms available | Term		2
Termination of lease instruments date		2020
Acccrued gain on lease termination					700,000
Irrevocable Standby Letter of Credit [Member]
Lessee Lease Description [Line Items]
Letter of credit			$ 1,500,000		$ 1,500,000
ASU 2016-02 [Member]
Lessee Lease Description [Line Items]
Cumulative effect on adjustment of initially applying standard	$ 0

Leases - Summary of Undiscounte

Leases - Summary of Undiscounted Cash Flows to Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Lessee Lease Description [Line Items]
Less: operating lease obligations, current portion	$ (4,198)	$ (4,080)
Operating lease obligations, long-term portion	42,103	$ 45,532
Facility Lease [Member]
Lessee Lease Description [Line Items]
Remainder of 2020	1,819
2021	7,524
2022	7,787
2023	8,064
2024	8,341
2025 and beyond	26,825
Total minimum lease payments	60,360
Less: amount of lease payments representing interest	(14,059)
Present value of future minimum lease payments	46,301
Less: operating lease obligations, current portion	(4,198)
Operating lease obligations, long-term portion	42,103
Facility Sublease [Member]
Lessee Lease Description [Line Items]
2021	2,547
2023	6,310
2024	7,476
2025 and beyond	24,034
Total minimum lease payments	$ 40,367

Restructuring and Other Charg_3

Restructuring and Other Charges - Additional Information (Detail) $ in Millions	1 Months Ended		3 Months Ended			9 Months Ended
	Oct. 31, 2019Position	Jan. 31, 2019Employees	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Mar. 31, 2019USD ($)	Sep. 30, 2020USD ($)
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]
Restructuring Cost And Reserve [Line Items]
Gain (loss) on disposition of assets			$ 0			$ 3.4
Laboratory equipment [Member] | 2019 Restructure Plan [Member]
Restructuring Cost And Reserve [Line Items]
Impairment loss on long lived assets				$ 1.9
Severance and Other Benefit Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges					$ 1.8

Restructuring and Other Charg_4

Restructuring and Other Charges - Summary of Management's Expected and Actual Costs (Detail) $ in Thousands	Sep. 30, 2020USD ($)
Restructuring Cost And Reserve [Line Items]
Total Estimated restructuring costs	$ 3,874
Total Restructuring cost incurred to date	3,365
Asset Impairments And Other Costs, Net Gains On Sale [Member]
Restructuring Cost And Reserve [Line Items]
Total Estimated restructuring costs	(3,298)
Total Restructuring cost incurred to date	(3,298)
Employee Retention, Severance and Termination Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Total Estimated restructuring costs	7,172
Total Restructuring cost incurred to date	$ 6,663

Restructuring and Other Charg_5

Restructuring and Other Charges - Summary of Components of Restructuring and Other Related Costs and their Location within Income Statement (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	$ 515	$ (3,251)	$ 1,893
Research and development [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	306	(3,711)	$ 1,893
General and administrative [Member]
Restructuring Cost And Reserve [Line Items]
Total Restructuring cost incurred	$ 209	$ 460

Restructuring and Other Charg_6

Restructuring and Other Charges - Summary of Accrued Personnel-related Expense Liability Associated with Restructuring (Detail) - Severance and Retention Costs [Member] $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Restructuring Cost And Reserve [Line Items]
Accrued balance as of December 31, 2019	$ 1,183
Charges	2,134
Cash payments	(1,646)
Accrued balance as of September 30, 2020	$ 1,671

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($)	Nov. 02, 2020	Aug. 06, 2020	Oct. 31, 2020	Sep. 30, 2020
Subsequent Event [Line Items]
Rent commencement date				Jan. 1, 2018
Lease term				10 years
Lease option additional extend term				5 years
Cowen and Company, LLC Sales Agreement [Member]
Subsequent Event [Line Items]
Aggregate offering price		$ 75,000,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Rent commencement date			Nov. 1, 2020
Lease term			2 months
Lease option additional extend term			2 months
Monthly fees for the space			$ 100,000
Subsequent Event [Member] | Cowen and Company, LLC Sales Agreement [Member]
Subsequent Event [Line Items]
Net proceeds from offering	$ 7,400,000