Five Prime Therapeutics (FPRX) 10-Q 6 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 05, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
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	Large 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		36,391,851

Balance Sheets (Unaudited)

Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 48,933	$ 43,953
Marketable securities	137,054	226,185
Receivables from collaborative partners	3,664	5,096
Prepaid and other current assets	7,841	13,334
Total current assets	197,492	288,568
Restricted cash	1,543	1,543
Property and equipment, net	25,759	28,718
Operating lease, right-of-use assets	31,546
Other long-term assets	2,200	2,705
Total assets	258,540	321,534
Current liabilities:
Accounts payable	4,234	1,972
Accrued personnel-related expenses	5,994	7,383
Other accrued liabilities	12,184	15,348
Operating lease obligations, current portion	3,944
Deferred revenue, current portion	2,153	1,428
Deferred rent, current portion		1,356
Total current liabilities	28,509	27,487
Deferred revenue, long-term portion	5,023	10,465
Operating lease obligations, long-term portion	46,574
Deferred rent, long-term portion		18,443
Stockholders' equity:
Common stock, $0.001 par value; 100,000,000 shares authorized, 36,421,709 issued and 35,099,100 outstanding at September 30, 2019; 35,625,751 issued and 34,745,721 outstanding at December 31, 2018.	34	34
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Additional paid-in capital	578,847	559,892
Accumulated other comprehensive income (loss)	79	(106)
Accumulated deficit	(400,526)	(294,681)
Total stockholders' equity	178,434	265,139
Total liabilities and stockholders' equity	$ 258,540	$ 321,534

Balance Sheets (Unaudited) (Par

Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
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	36,421,709	35,625,751
Common stock, shares outstanding	35,099,100	34,745,721
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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Collaboration revenue	$ 2,984	$ 5,771	$ 11,664	$ 45,837
Type of Revenue [Extensible List]	fprx:CollaborationMember	fprx:CollaborationMember	fprx:CollaborationMember	fprx:CollaborationMember
Operating expenses:
Research and development	$ 26,948	$ 44,687	$ 88,126	$ 121,619
General and administrative	13,206	9,832	33,377	30,092
Total operating expenses	40,154	54,519	121,503	151,711
Loss from operations	(37,170)	(48,748)	(109,839)	(105,874)
Interest income	1,100	1,531	3,996	4,212
Other expense, net	1	(27)	(2)	(32)
Loss before income tax	(36,069)	(47,244)	(105,845)	(101,694)
Net loss	$ (36,069)	$ (47,244)	$ (105,845)	$ (101,694)
Basic and diluted net loss per common share	$ (1.03)	$ (1.37)	$ (3.03)	$ (3.01)
Weighted-average shares used to compute basic and diluted net loss per common share	34,996	34,482	34,901	33,740

Statements of Comprehensive Los

Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (36,069)	$ (47,244)	$ (105,845)	$ (101,694)
Other comprehensive gain:
Unrealized gain/(loss) on marketable securities	(63)	128	185	226
Comprehensive loss	$ (36,132)	$ (47,116)	$ (105,660)	$ (101,468)

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, 2017	$ 265,202	$ 28	$ 421,257	$ (476)	$ (155,607)
Beginning Balance, Shares at Dec. 31, 2017		28,178,639
Issuance of common stock upon follow-on public offering, net of issuance costs	115,000	$ 6	114,994
Issuance of stock, Shares		5,897,435
Issuance costs related to the follow-on public offering	(7,387)		(7,387)
Issuance of common stock under equity incentive plans	1,704		1,704
Issuance of common stock under equity incentive plans, Shares		311,179
Repurchase of shares to satisfy tax withholding obligations	(997)		(997)
Repurchase of shares to satisfy tax withholding obligations, Shares		(52,608)
Cumulative effect of adoption of ASU | ASU 2014-09 [Member]	1,374				1,374
Stock-based compensation expense	7,820		7,820
Other comprehensive gain (loss)	(110)			(110)
Net loss	(20,390)				(20,390)
Ending Balance at Mar. 31, 2018	362,216	$ 34	537,391	(586)	(174,623)
Ending Balance, Shares at Mar. 31, 2018		34,334,645
Beginning Balance at Dec. 31, 2017	265,202	$ 28	421,257	(476)	(155,607)
Beginning Balance, Shares at Dec. 31, 2017		28,178,639
Net loss	(101,694)
Ending Balance at Sep. 30, 2018	296,778	$ 34	552,921	(250)	(255,927)
Ending Balance, Shares at Sep. 30, 2018		34,531,817
Beginning Balance at Mar. 31, 2018	362,216	$ 34	537,391	(586)	(174,623)
Beginning Balance, Shares at Mar. 31, 2018		34,334,645
Issuance of common stock under equity incentive plans	1,160		1,160
Issuance of common stock under equity incentive plans, Shares		122,278
Repurchase of shares to satisfy tax withholding obligations	(101)		(101)
Repurchase of shares to satisfy tax withholding obligations, Shares		(5,766)
Stock-based compensation expense	7,435		7,435
In transit: issuance of common stock under equity incentive plans, Shares		3,661
In transit: repurchase of shares to satisfy tax withholding, Shares		(4,365)
Other comprehensive gain (loss)	208			208
Net loss	(34,060)				(34,060)
Ending Balance at Jun. 30, 2018	336,858	$ 34	545,885	(378)	(208,683)
Ending Balance, Shares at Jun. 30, 2018		34,450,453
Issuance of common stock under equity incentive plans	158		158
Issuance of common stock under equity incentive plans, Shares		129,022
Repurchase of shares to satisfy tax withholding obligations	(757)		(757)
Repurchase of shares to satisfy tax withholding obligations, Shares		(47,658)
Stock-based compensation expense	7,634		7,634
Other comprehensive gain (loss)	128			128
Net loss	(47,244)				(47,244)
Ending Balance at Sep. 30, 2018	296,778	$ 34	552,921	(250)	(255,927)
Ending Balance, Shares at Sep. 30, 2018		34,531,817
Beginning Balance at Dec. 31, 2018	$ 265,139	$ 34	559,892	(106)	(294,681)
Beginning Balance, Shares at Dec. 31, 2018	34,745,721	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	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	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	35,099,100

Statements of Cash Flows (Unaud

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net loss	$ (105,845)	$ (101,694)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,850	3,729
Stock-based compensation expense	19,391	22,889
Amortization of discounts and premiums on marketable securities	(1,925)	(984)
Non-cash operating lease expense	1,739
Loss on disposal of property and equipment		5
Changes in operating assets and liabilities:
Receivables from collaborative partners	1,432	8,118
Prepaid, other current assets and other long-term assets	5,413	(3,015)
Accounts payable	2,978	258
Accrued personnel-related expenses	(1,389)	(342)
Deferred revenue	(4,717)	(8,475)
Deferred rent		1,026
Other accrued liabilities, and other long-term liabilities	(3,175)	8,549
Operating lease liabilities	(1,999)
Net cash used in operating activities	(84,247)	(69,936)
Investing activities
Purchases of marketable securities	(180,551)	(282,443)
Maturities of marketable securities	271,792	259,000
Purchases of property and equipment	(1,578)	(11,147)
Net cash provided by (used in) investing activities	89,663	(34,590)
Financing activities
Proceeds from public offering of common stock, net of issuance costs		107,613
Proceeds from issuance of common stock under equity incentive plans	998	3,023
Repurchase of shares to satisfy tax withholding obligations	(1,434)	(1,855)
Net cash provided by (used in) financing activities	(436)	108,781
Net decrease in cash and cash equivalents and restricted cash	4,980	4,255
Cash, cash equivalents and restricted cash at beginning of period	45,496	61,333
Cash, cash equivalents and restricted cash at end of period	50,476	65,588
Supplemental disclosure
Property and equipment purchases included in accrued liabilities	29	132
Supplemental cash flow information
Cash and cash equivalents at beginning of period	43,953	59,790
Restricted cash at beginning of period	1,543	1,543
Cash, cash equivalents and restricted cash at beginning of period	45,496	61,333
Cash and cash equivalents at end of period	48,933	64,045
Restricted cash at end of period	1,543	1,543
Cash, cash equivalents and restricted cash at end of period	$ 50,476	$ 65,588

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2019
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, 2019 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 consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying 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, 2018, filed with the U.S. Securities and Exchange Commission, or the SEC, on February 26, 2019, or our Annual Report.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
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. 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 of Financial Instruments We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. We do not have any assets or liabilities measured using Level 3 inputs as of September 30, 2019 . 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, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds 25,119 $ 25,119 $ — $ — U.S. Treasury securities 37,183 37,183 — — Agency bonds 61,546 61,546 — — Corporate bonds 4,798 — 4,798 — Commercial paper 33,527 — 33,527 — Certificate of deposit 1,543 — 1,543 — Total $ 163,716 $ 123,848 $ 39,868 $ — December 31, 2018 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 40,849 $ 40,849 $ — $ — U.S. Treasury securities 104,140 104,140 — — Agency bonds 53,999 53,999 — — Corporate bonds 11,893 — 11,893 — Commercial paper 56,152 — 56,152 — Certificate of deposit 1,543 — 1,543 — Total $ 268,576 $ 198,988 $ 69,588 $ — Revenue Recognition Effective January 1, 2018, we adopted Financial Accounting Standards Board, or FASB, Accounting Standard Update, or ASU , Revenue from Contracts with Customers (Topic 606) The terms of our 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 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, 2019 2018 2019 2018 Options to purchase common stock 3,706 3,830 3,868 3,934 Restricted stock awards (RSAs) 1,728 1,078 1,313 975 5,434 4,908 5,181 4,909 Accounting Pronouncements Adopted in 2019 In February 2016, FASB issued ASU 2016-02, Leases (Topic 842) We adopted the standard, effective January 1, 2019, using the updated modified retrospective transition method, in which the new standard is applied as of the date of initial adoption. We recognized and measured agreements executed prior to the date of initial adoption that were considered leases on January 1, 2019. No cumulative effect adjustment of initially applying the standard to the opening balance of retained earnings was made upon adoption. We elected the package of practical expedients permitted under the transition guidance that will r etain the lease classification and initial direct costs for any leases that exist prior to adoption of the standard. We have not reassessed whether any contracts entered into prior to adoption are leases Upon adoption, we derecognized $19.8 million in deferred rent and ecognized $52.5 million in lease liabilities and $33.3 million in right-of-use assets on our balance sheet In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification. These amendments eliminate, modify, or integrate into other SEC requirements certain disclosure rules. Among the amendments is the requirement to present an analysis of changes in stockholders’ equity in the interim financial statements included in quarterly reports on Form 10-Q. The analysis, which can be presented as a footnote or separate statement, is required for the current and comparative quarters and year-to-date interim periods. The amendments are effective for all filings made on or after November 5, 2018. In light of the anticipated timing of effectiveness of the amendments and expected proximity of effectiveness to the filing date for most filers’ quarterly reports, the SEC’s Division of Corporate Finance issued a Compliance and Disclosure Interpretation related to Exchange Act Forms, or CDI – Question 105.09, which provides transition guidance related to this disclosure requirement. CDI – Question 105.09 states that the SEC would not object if the filer’s first presentation of the changes in shareholders’ equity is included in its quarterly report on Form 10-Q for the quarter that begins after the effective date of the amendments. As such, we adopted these SEC amendments on November 5, 2018 and presented the analysis of changes in stockholders’ equity beginning the first quarter of 2019. No adjustment was required as a result of this adoption. Accounting Pronouncements Not Yet Adopted 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. ASU 2018-18 will become effective January 1, 2020 and will apply to all annual and interim reporting periods thereafter. Early adoption is permitted. ASU 2018-18 should generally be applied retrospectively to the date of initial application of Topic 606. We do not anticipate that the adoption of this standard will have a material effect on our financial statements. In August 2018, FASB issued ASU 2018-13, Fair Value Measurement–Disclosure Framework (Topic 820) 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)

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	9 Months Ended
	Sep. 30, 2019
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	3. Cash Equivalents and Marketable Securities The following table summarizes our cash equivalents and marketable securities (in thousands): September 30, 2019 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 25,118 $ 1 $ — $ 25,119 U.S. Treasury securities 37,168 17 (2 ) 37,183 Agency bonds 61,489 59 (1 ) 61,547 Corporate bonds 4,796 1 — 4,797 Commercial paper 33,522 6 (1 ) 33,527 Total cash equivalents and marketable securities 162,093 84 (4 ) 162,173 Less: cash equivalents (25,118 ) (1 ) — (25,119 ) Total marketable securities $ 136,975 $ 83 $ (4 ) $ 137,054 December 31, 2018 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 40,849 $ — $ — $ 40,849 U.S. Treasury securities 104,218 — (78 ) 104,140 Agency bonds 54,005 9 (15 ) 53,999 Corporate bonds 11,897 — (4 ) 11,893 Commercial paper 56,171 — (19 ) 56,152 Total cash equivalents and marketable securities 267,140 9 (115 ) 267,034 Less: cash equivalents (40,849 ) — — (40,849 ) Total marketable securities $ 226,291 $ 9 $ (115 ) $ 226,185 As of September 30, 2019, 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 $ 136,975 $ 137,054 Total marketable securities $ 136,975 $ 137,054 We determined that the gross unrealized losses on our marketable securities as of September 30, 2019 were temporary in nature. We currently do not intend to sell these securities prior to maturity and do not consider these investments to be other-than-temporarily impaired at September 30, 2019. There were no sales of available-for-sale securities in any of the periods presented.

Equity Incentive Plans

Equity Incentive Plans	9 Months Ended
	Sep. 30, 2019
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, 2018 3,710,181 $ 28.37 Options granted 1,152,319 9.55 Options exercised (41,892 ) 8.09 Options forfeited (777,203 ) 26.29 Options expired (652,691 ) 34.05 Balance at September 30, 2019 3,390,714 21.61 5.66 Options exercisable at September 30, 2019 2,191,180 25.29 4.24 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, 2018 880,030 $ 26.36 RSAs granted 1,490,200 8.07 RSAs vested (420,138 ) 20.65 RSAs forfeited (627,483 ) 16.45 Unvested balance at September 30, 2019 1,322,609 12.27 As of September 30, 2019, there were 2,724,275 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, 2019 2018 2019 2018 Research and development $ 2,323 $ 4,084 $ 6,706 $ 12,073 General and administrative 6,333 3,549 12,685 10,816 Total $ 8,656 $ 7,633 $ 19,391 $ 22,889 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, 2019 2018 2019 2018 Expected term (years) 5.3-6.0 6.3 5.3-6.3 5.5-6.3 Expected volatility 67.0% 67.9% 67.0-67.7% 67.9-69.8% Risk-free interest rate 1.6-1.7% 2.9% 1.6-2.5% 2.6-2.9% Expected dividend yield 0% 0% 0% 0% As of September 30, 2019, we had $12.3 million of total unrecognized compensation expense related to unvested stock options that we expect to recognize over a weighted-average period of 2.3 years. Additionally, we had $8.5 million of total unrecognized compensation expense related to employee and director RSAs that we expect to recognize over a weighted-average period of 1.9 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. We are recognizing the incremental expense of $0.2 million for new options 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 $2.8 million as of September 30, 2019 over the remainder of the original requisite service period.

License and Collaboration Arran

License and Collaboration Arrangements	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Arrangements	5. License and Collaboration Arrangements See Note 8 to the audited consolidated financial statements included in Part IV, Item 15 of our Annual Report for information on our license and collaboration agreements. The following table presents changes during the nine months ended September 30, 2019 in the balances of our contract assets, including receivables from collaboration partners, and contract liabilities, including deferred revenue, as compared to what we disclosed in our Annual Report. (in thousands) Contract Assets Balance at December 31, 2018 $ 5,096 Additions 6,950 Deductions (8,382 ) Balance at September 30, 2019 $ 3,664 (in thousands) Contract Liabilities Balance at December 31, 2018 $ 11,893 Additions for advance billings 1,807 Deductions for performance obligations satisfied in current period (4,544 ) Deductions for performance obligations satisfied in the prior periods in connection with updates to the measure of progress (1,980 ) Balance at September 30, 2019 $ 7,176 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, 2019, 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 and $1.4 million for the three and nine months ended September 30, 2019, respectively. License 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 ® For the three and nine months ended September 30, 2019, no adjustments were made to the transaction price. 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. We recognized $0.9 million and $3.8 million of the transaction price as revenue for the three and nine months ended September 30, 2019, respectively. Total revenue recognized for reimbursements for the three and nine months ended September 30, 2019 was $0.7 million and $3.1 million, respectively. Through September 30, 2019, we recognized $28.5 million of the transaction price as collaboration revenue under the original collaboration agreement. The remaining transaction price of $1.5 million is recorded as deferred revenue as of September 30, 2019 and will be recognized as revenue under the input method over the estimated performance period. Under the cabiralizumab collaboration agreement, we identified the following performance obligations: (1) 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, 2019, 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 identified the following performance obligations: (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 $14.7 million consists of the $8.8 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 estimated the $8.8 million of expected reimbursements from Zai Lab based on the probability-weighted amounts of a range of possible consideration amounts. We have not included the 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. For the three and nine months ended September 30, 2019, no adjustments were made to the transaction price. We use the input method to measure progress toward completion of the performance obligation for the license. 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. For the three and nine months ended September 30, 2019, revenue recognized for the license grant performance obligation was $0.4 million and $1.0 million, respectively. Total revenue recognized for the companion diagnostics development performance obligation was $1.0 million and $2.4 million for the three and nine months ended September 30, 2019, respectively. Of the remaining transaction price of $11.9 million, we recorded $5.0 million in deferred revenue, which we will recognize over the estimated performance period for satisfaction of the performance obligations. The remaining $6.9 million of the transaction price will be recorded in deferred revenue when invoiced as we complete global development activities. Glaxo Group Limited In April 2012, we entered into a research collaboration and license agreement, or the respiratory diseases collaboration, with Glaxo Group Limited, or GSK, to identify new therapeutic approaches to treat refractory asthma and chronic obstructive pulmonary disease, or COPD, with a particular focus on identifying novel protein therapeutics and antibody targets. In January 2016, we amended our respiratory diseases collaboration to extend the research term by three months to July 2016 to allow additional validation of the protein targets we discovered and to increase the research funding. Under the respiratory diseases collaboration, we identified one performance obligation for the research license and research activities. The non-refundable upfront fee, the equity premium and the were included as part of the transaction price. As t transaction price was fully recognized in prior years. The clinical and regulatory development milestone payments have not been included in the transaction price, as all such milestone amounts are fully constrained. 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. Under the , additional research funding that GSK had the option to add was also not included in the transaction price. We will re-evaluate the transaction price for the in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three and nine months ended September 30, 2019, no adjustments were made to the transaction price. UCB Pharma, S.A. In March 2013, we entered into a research collaboration and license agreement, or the fibrosis and CNS collaboration, with UCB Pharma, S.A., or UCB, to identify potential biologics targets and therapeutics in the areas of fibrosis-related immunologic diseases and central nervous system, or CNS, disorders. Under the fibrosis and CNS collaboration, we identified research activities as our only performance obligation. UCB’s options to select additional collaboration targets and to license exclusive rights to selected targets are not priced at a discount and therefore do not represent performance obligations for which the transaction price would be allocated. The transaction price of $15.6 million includes the $6.0 million non-refundable upfront fee, the $6.6 million technology access fee, the $1.0 million reimbursement for reagent costs and the $2.0 million of research funding. As t transaction price of $15.6 million was fully recognized in 2018. We have not included the clinical and regulatory development milestone payments in the transaction price as all such milestone amounts are fully constrained. We will recognize any consideration related to sales-based 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 in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three and nine months ended September 30, 2019, no adjustments were made to the transaction price.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	6. Leases We adopted ASU 2016-02, effective January 1, 2019, using the updated modified retrospective transition method, in which the new standard is applied as of the date of initial adoption. We recognized and measured agreements executed prior to the date of initial adoption that were considered leases on January 1, 2019. No cumulative effect adjustment of initially applying the standard to the opening balance of retained earnings was made upon adoption. We elected the package of practical expedients permitted under the transition guidance that will r 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 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 our new 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. In October 2019, we commenced a corporate restructuring to extend our cash runway and ensure long-term sustainability. As part of the restructuring, we are initiating activities to reduce our corporate facilities footprint by either subletting a significant portion of our current leased space or subletting our current building and relocating to smaller facilities. 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 terms based on delivery dates for the first three instruments in July 2018 and the fourth instrument in February 2019. The instruments lease contains consistent rent payments over the term of the lease. 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 recognize operating lease cost as a single lease cost, calculated so that the cost of the lease is allocated over the lease term on a straight-line basis. 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 the measurement of operating lease liabilities was $ 1.9 million and $ 4.9 million for the three and nine months ended September 30, 2019. The weighted-average discount rate of our operating leases is 7%, and the weighted-average remaining lease term of our operating leases is eight years as of September 30, 2019. The table below reconciles the undiscounted cash flows for each of the first five years and the total of the remaining years to the operating lease labilities recorded on the balance sheet. Operating Leases Remainder of 2019 $ 1,853 Years ending December 31, 2020 7,564 2021 7,723 2022 7,799 2023 8,064 2024 and on 35,166 Total minimum lease payments $ 68,169 Less: amount of lease payments representing interest (17,651 ) Present value of future minimum lease payments $ 50,518 Less: operating lease obligations, current portion (3,944 ) Operating lease obligations, long-term portion $ 46,574

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2019
Subsequent Events [Abstract]
Subsequent Event	7. Subsequent Event In October 2019, we implemented a corporate restructuring to extend our cash runway and ensure long-term sustainability. As part of the restructuring, we will reduce our workforce by approximately 70 positions across all functions at the company. A pproximately 70% of the eliminations will occur by the end of 2019, with the remainder occurring in 2020. In addition, we are initiating activities to reduce our corporate facilities footprint by either subletting a significant portion of our current leased space or subletting our current building and relocating to smaller facilities. In connection with the restructuring, we anticipate we will incur approximately $6.0 million of pre-tax charges for severance and other personnel-related costs. This amount includes $1.2 million for pro-rated bonuses earned by and payable to each employee terminated in the restructuring pursuant to the company’s annual bonus plan, calculated on the assumption that such bonuses will be paid at 100% of the bonus target amount applicable to each terminated employee based on the company’s and each such terminated employee’s 2019 performance. We will determine the company’s and each terminated employee’s performance against 2019 goals and, accordingly, each terminated employee’s actual pro-rated 2019 bonus amount in the first quarter of 2020 in connection with our annual review process. Further, the $6.0 million also includes $2.0 million of retention bonuses for non-terminated employees who remain employed with the company through December 31, 2020, based on the assumption that all such employees will remain employed by the company through December 31, 2020. In the event an employee’s employment is voluntary terminated, or involuntarily terminated with cause, the retention bonus for that employee will not be paid.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
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.
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 of Financial Instruments	Fair Value of Financial Instruments We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. We do not have any assets or liabilities measured using Level 3 inputs as of September 30, 2019 . 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, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds 25,119 $ 25,119 $ — $ — U.S. Treasury securities 37,183 37,183 — — Agency bonds 61,546 61,546 — — Corporate bonds 4,798 — 4,798 — Commercial paper 33,527 — 33,527 — Certificate of deposit 1,543 — 1,543 — Total $ 163,716 $ 123,848 $ 39,868 $ — December 31, 2018 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 40,849 $ 40,849 $ — $ — U.S. Treasury securities 104,140 104,140 — — Agency bonds 53,999 53,999 — — Corporate bonds 11,893 — 11,893 — Commercial paper 56,152 — 56,152 — Certificate of deposit 1,543 — 1,543 — Total $ 268,576 $ 198,988 $ 69,588 $ —
Revenue Recognition	Revenue Recognition Effective January 1, 2018, we adopted Financial Accounting Standards Board, or FASB, Accounting Standard Update, or ASU , Revenue from Contracts with Customers (Topic 606) The terms of our 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 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, 2019 2018 2019 2018 Options to purchase common stock 3,706 3,830 3,868 3,934 Restricted stock awards (RSAs) 1,728 1,078 1,313 975 5,434 4,908 5,181 4,909
Accounting Pronouncements Adopted in 2019	Accounting Pronouncements Adopted in 2019 In February 2016, FASB issued ASU 2016-02, Leases (Topic 842) We adopted the standard, effective January 1, 2019, using the updated modified retrospective transition method, in which the new standard is applied as of the date of initial adoption. We recognized and measured agreements executed prior to the date of initial adoption that were considered leases on January 1, 2019. No cumulative effect adjustment of initially applying the standard to the opening balance of retained earnings was made upon adoption. We elected the package of practical expedients permitted under the transition guidance that will r etain the lease classification and initial direct costs for any leases that exist prior to adoption of the standard. We have not reassessed whether any contracts entered into prior to adoption are leases Upon adoption, we derecognized $19.8 million in deferred rent and ecognized $52.5 million in lease liabilities and $33.3 million in right-of-use assets on our balance sheet In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification. These amendments eliminate, modify, or integrate into other SEC requirements certain disclosure rules. Among the amendments is the requirement to present an analysis of changes in stockholders’ equity in the interim financial statements included in quarterly reports on Form 10-Q. The analysis, which can be presented as a footnote or separate statement, is required for the current and comparative quarters and year-to-date interim periods. The amendments are effective for all filings made on or after November 5, 2018. In light of the anticipated timing of effectiveness of the amendments and expected proximity of effectiveness to the filing date for most filers’ quarterly reports, the SEC’s Division of Corporate Finance issued a Compliance and Disclosure Interpretation related to Exchange Act Forms, or CDI – Question 105.09, which provides transition guidance related to this disclosure requirement. CDI – Question 105.09 states that the SEC would not object if the filer’s first presentation of the changes in shareholders’ equity is included in its quarterly report on Form 10-Q for the quarter that begins after the effective date of the amendments. As such, we adopted these SEC amendments on November 5, 2018 and presented the analysis of changes in stockholders’ equity beginning the first quarter of 2019. No adjustment was required as a result of this adoption.
Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Not Yet Adopted 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. ASU 2018-18 will become effective January 1, 2020 and will apply to all annual and interim reporting periods thereafter. Early adoption is permitted. ASU 2018-18 should generally be applied retrospectively to the date of initial application of Topic 606. We do not anticipate that the adoption of this standard will have a material effect on our financial statements. In August 2018, FASB issued ASU 2018-13, Fair Value Measurement–Disclosure Framework (Topic 820) 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)

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds 25,119 $ 25,119 $ — $ — U.S. Treasury securities 37,183 37,183 — — Agency bonds 61,546 61,546 — — Corporate bonds 4,798 — 4,798 — Commercial paper 33,527 — 33,527 — Certificate of deposit 1,543 — 1,543 — Total $ 163,716 $ 123,848 $ 39,868 $ — December 31, 2018 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 40,849 $ 40,849 $ — $ — U.S. Treasury securities 104,140 104,140 — — Agency bonds 53,999 53,999 — — Corporate bonds 11,893 — 11,893 — Commercial paper 56,152 — 56,152 — Certificate of deposit 1,543 — 1,543 — Total $ 268,576 $ 198,988 $ 69,588 $ —
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, 2019 2018 2019 2018 Options to purchase common stock 3,706 3,830 3,868 3,934 Restricted stock awards (RSAs) 1,728 1,078 1,313 975 5,434 4,908 5,181 4,909

Cash Equivalents and Marketab_2

Cash Equivalents and Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Cash And Cash Equivalents [Abstract]
Summary of Cash Equivalents and Marketable Securities	The following table summarizes our cash equivalents and marketable securities (in thousands): September 30, 2019 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 25,118 $ 1 $ — $ 25,119 U.S. Treasury securities 37,168 17 (2 ) 37,183 Agency bonds 61,489 59 (1 ) 61,547 Corporate bonds 4,796 1 — 4,797 Commercial paper 33,522 6 (1 ) 33,527 Total cash equivalents and marketable securities 162,093 84 (4 ) 162,173 Less: cash equivalents (25,118 ) (1 ) — (25,119 ) Total marketable securities $ 136,975 $ 83 $ (4 ) $ 137,054 December 31, 2018 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 40,849 $ — $ — $ 40,849 U.S. Treasury securities 104,218 — (78 ) 104,140 Agency bonds 54,005 9 (15 ) 53,999 Corporate bonds 11,897 — (4 ) 11,893 Commercial paper 56,171 — (19 ) 56,152 Total cash equivalents and marketable securities 267,140 9 (115 ) 267,034 Less: cash equivalents (40,849 ) — — (40,849 ) Total marketable securities $ 226,291 $ 9 $ (115 ) $ 226,185
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	As of September 30, 2019, 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 $ 136,975 $ 137,054 Total marketable securities $ 136,975 $ 137,054

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2018 3,710,181 $ 28.37 Options granted 1,152,319 9.55 Options exercised (41,892 ) 8.09 Options forfeited (777,203 ) 26.29 Options expired (652,691 ) 34.05 Balance at September 30, 2019 3,390,714 21.61 5.66 Options exercisable at September 30, 2019 2,191,180 25.29 4.24
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, 2018 880,030 $ 26.36 RSAs granted 1,490,200 8.07 RSAs vested (420,138 ) 20.65 RSAs forfeited (627,483 ) 16.45 Unvested balance at September 30, 2019 1,322,609 12.27
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, 2019 2018 2019 2018 Research and development $ 2,323 $ 4,084 $ 6,706 $ 12,073 General and administrative 6,333 3,549 12,685 10,816 Total $ 8,656 $ 7,633 $ 19,391 $ 22,889
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, 2019 2018 2019 2018 Expected term (years) 5.3-6.0 6.3 5.3-6.3 5.5-6.3 Expected volatility 67.0% 67.9% 67.0-67.7% 67.9-69.8% Risk-free interest rate 1.6-1.7% 2.9% 1.6-2.5% 2.6-2.9% Expected dividend yield 0% 0% 0% 0%

License and Collaboration Arr_2

License and Collaboration Arrangements (Tables)	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Changes in Balances of Contract Assets and Contract Liabilities	The following table presents changes during the nine months ended September 30, 2019 in the balances of our contract assets, including receivables from collaboration partners, and contract liabilities, including deferred revenue, as compared to what we disclosed in our Annual Report. (in thousands) Contract Assets Balance at December 31, 2018 $ 5,096 Additions 6,950 Deductions (8,382 ) Balance at September 30, 2019 $ 3,664 (in thousands) Contract Liabilities Balance at December 31, 2018 $ 11,893 Additions for advance billings 1,807 Deductions for performance obligations satisfied in current period (4,544 ) Deductions for performance obligations satisfied in the prior periods in connection with updates to the measure of progress (1,980 ) Balance at September 30, 2019 $ 7,176

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Operating Lease Liabilities Payments Due [Abstract]
Summary of Undiscounted Cash Flows to Operating Lease Liabilities	The table below reconciles the undiscounted cash flows for each of the first five years and the total of the remaining years to the operating lease labilities recorded on the balance sheet. Operating Leases Remainder of 2019 $ 1,853 Years ending December 31, 2020 7,564 2021 7,723 2022 7,799 2023 8,064 2024 and on 35,166 Total minimum lease payments $ 68,169 Less: amount of lease payments representing interest (17,651 ) Present value of future minimum lease payments $ 50,518 Less: operating lease obligations, current portion (3,944 ) Operating lease obligations, long-term portion $ 46,574

Description of Business - Addit

Description of Business - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2019Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	Sep. 30, 2019	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Fair value, assets, level 1 to level 2 transfers	$ 0
Fair value, assets, level 2 to level 1 transfer	0
Lease liability	50,518,000
Right-of use assets	31,546,000
ASU 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect on adjustment of initially applying the standards		$ 0
Lease liability	52,500,000
Deferred rent derecognized	19,800,000
Right-of use assets	$ 33,300,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets
Total	$ 163,716	$ 268,576
Money market funds [Member]
Assets
Cash equivalents	25,119	40,849
Agency Bonds [Member]
Assets
Cash equivalents	61,546	53,999
Corporate bonds [Member]
Assets
Cash equivalents	4,798	11,893
Commercial paper [Member]
Assets
Cash equivalents	33,527	56,152
Certificate of deposit [Member]
Assets
Cash equivalents	1,543	1,543
Level 1 [Member]
Assets
Total	123,848	198,988
Level 1 [Member] | Money market funds [Member]
Assets
Cash equivalents	25,119	40,849
Level 1 [Member] | Agency Bonds [Member]
Assets
Cash equivalents	61,546	53,999
Level 2 [Member]
Assets
Total	39,868	69,588
Level 2 [Member] | Corporate bonds [Member]
Assets
Cash equivalents	4,798	11,893
Level 2 [Member] | Commercial paper [Member]
Assets
Cash equivalents	33,527	56,152
Level 2 [Member] | Certificate of deposit [Member]
Assets
Cash equivalents	1,543	1,543
U.S. Treasury securities [Member]
Assets
U.S. Treasury securities	37,183	104,140
U.S. Treasury securities [Member] | Level 1 [Member]
Assets
U.S. Treasury securities	$ 37,183	$ 104,140

Summary of Significant Accoun_6

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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	5,434	4,908	5,181	4,909
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	3,706	3,830	3,868	3,934
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	1,728	1,078	1,313	975

Cash Equivalents and Marketab_3

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 136,975	$ 226,291
Unrealized Gains	83	9
Unrealized Losses	(4)	(115)
Estimated Fair Value	137,054	226,185
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	25,118	40,849
Unrealized Gains	1
Estimated Fair Value	25,119	40,849
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	37,168	104,218
Unrealized Gains	17
Unrealized Losses	(2)	(78)
Estimated Fair Value	37,183	104,140
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	61,489	54,005
Unrealized Gains	59	9
Unrealized Losses	(1)	(15)
Estimated Fair Value	61,547	53,999
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	4,796	11,897
Unrealized Gains	1
Unrealized Losses		(4)
Estimated Fair Value	4,797	11,893
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	33,522	56,171
Unrealized Gains	6
Unrealized Losses	(1)	(19)
Estimated Fair Value	33,527	56,152
Total cash equivalents and marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	162,093	267,140
Unrealized Gains	84	9
Unrealized Losses	(4)	(115)
Estimated Fair Value	162,173	267,034
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	(25,118)	(40,849)
Unrealized Gains	(1)
Estimated Fair Value	$ (25,119)	$ (40,849)

Cash Equivalents and Marketab_4

Cash Equivalents and Marketable Securities - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available For Sale Securities Debt Maturities [Abstract]
Amortized Cost, In one year or less	$ 136,975
Amortized Cost Basis	136,975	$ 226,291
Estimated Fair Value, In one year or less	137,054
Total marketable securities, Estimated Fair Value	$ 137,054	$ 226,185

Cash Equivalents and Marketab_5

Cash Equivalents and Marketable Securities - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2019USD ($)
Investments Debt And Equity Securities [Abstract]
Sales of available-for-sale securities	$ 0

Equity Incentive Plans - Schedu

Equity Incentive Plans - Schedule of Option Activity under Equity Incentive Plans and Related Information (Detail)	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance | shares	3,710,181
Number of Shares, Options granted | shares	1,152,319
Number of Shares, Options exercised | shares	(41,892)
Number of Shares, Options forfeited | shares	(777,203)
Number of Shares, Options expired | shares	(652,691)
Number of Shares, Ending balance | shares	3,390,714
Number of Shares, Options exercisable | shares	2,191,180
Weighted-Average Exercise Price Per Share, Options beginning balance | $ / shares	$ 28.37
Weighted-Average Exercise Price Per Share, Options granted | $ / shares	9.55
Weighted-Average Exercise Price Per Share, Options exercised | $ / shares	8.09
Weighted-Average Exercise Price Per Share, Options forfeited | $ / shares	26.29
Weighted-Average Exercise Price Per Share, Options expired | $ / shares	34.05
Weighted-Average Exercise Price Per Share, Options ending balance | $ / shares	21.61
Weighted-Average Exercise Price Per Share, Options exercisable | $ / shares	$ 25.29
Weighted-Average Remaining Contractual Terms, Options ending balance	5 years 7 months 28 days
Weighted-Average Remaining Contractual Term, Options exercisable	4 years 2 months 26 days

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, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Unvested, beginning balance | shares	880,030
Number of Shares, Granted | shares	1,490,200
Number of Shares, Vested | shares	(420,138)
Number of Shares, Forfeited | shares	(627,483)
Number of Shares, Unvested, Ending balance | shares	1,322,609
Weighted-Average Grant-Date Fair Value, Unvested, Beginning balance | $ / shares	$ 26.36
Weighted-Average Grant-Date Fair Value, Granted | $ / shares	8.07
Weighted-Average Grant-Date Fair Value, Vested | $ / shares	20.65
Weighted-Average Grant-Date Fair Value, Forfeited | $ / shares	16.45
Weighted-Average Grant-Date Fair Value, Unvested, Ending balance | $ / shares	$ 12.27

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Detail) $ / shares in Units, $ in Millions	Jul. 29, 2019USD ($)Employee$ / sharesshares	Sep. 30, 2019USD ($)$ / 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 | $		$ 12.3
Unrecognized compensation expense expected to recognize, weighted-average period		2 years 3 months 18 days
Exercise price per share, new options granted | $ / shares		$ 9.55
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense expected to recognize, weighted-average period		1 year 10 months 24 days
Total unrecognized compensation expense related to employee and director RSAs | $		$ 8.5
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 | shares	201,229	2,724,275
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 | shares	510,932
Number of employees elected to exchange outstanding stock options | Employee	55
Number of shares cancelled in conjunction with the option exchange offer | shares	436,648
Percentage of eligible options to total shares of common stock	85.00%
Number of shares granted for new options | shares	235,419
Exercise price per share, new options granted | $ / shares	$ 5.06
Incremental expense | $	$ 0.2
Unamortized expense remaining on the tendered options | $		$ 2.8

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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 8,656	$ 7,633	$ 19,391	$ 22,889
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	2,323	4,084	6,706	12,073
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 6,333	$ 3,549	$ 12,685	$ 10,816

Equity Incentive Plans - Sche_4

Equity Incentive Plans - Schedule of Stock Options Assumptions (Detail) - Options [Member]	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		6 years 3 months 18 days
Expected volatility	67.00%	67.90%
Risk-free interest rate		2.90%
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)	5 years 3 months 18 days		5 years 3 months 18 days	5 years 6 months
Expected volatility			67.00%	67.90%
Risk-free interest rate	1.60%		1.60%	2.60%
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			67.70%	69.80%
Risk-free interest rate	1.70%		2.50%	2.90%

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, 2019USD ($)
Contract With Customer Asset And Liability [Abstract]
Beginning balance	$ 5,096
Additions	6,950
Deductions	(8,382)
Ending balance	3,664
Beginning balance	11,893
Additions for advance billings	1,807
Deductions for performance obligations satisfied in current period	(4,544)
Deductions for performance obligations satisfied in the prior periods in connection with updates to the measure of progress	(1,980)
Ending balance	$ 7,176

License and Collaboration Arr_4

License and Collaboration Arrangements - Additional Information (Detail) - USD ($)	Oct. 14, 2015	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2015	Sep. 30, 2019	Mar. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized		$ 2,984,000	$ 5,771,000	$ 11,664,000	$ 45,837,000
Transaction price recognized as collaboration revenue				4,544,000
Bristol-Myers Squibb Company [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable up-front fee	$ 30,000,000
Adjustments to transaction price		0		$ 0
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 | 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		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							$ 28,500,000
License and collaboration agreement entered date				Oct. 14, 2015
Remaining transaction price recorded in deferred revenue		1,500,000		$ 1,500,000			1,500,000
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		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		900,000		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		0		0
Revenue recognized		1,000,000		2,400,000
Remaining transaction price recorded in deferred revenue		5,000,000		$ 5,000,000			5,000,000
License and collaboration agreement entered month and year				2017-12
Collaboration and license agreements transaction price				$ 14,700,000
Expected reimbursements		8,800,000		8,800,000			8,800,000
Receivables related to collaboration agreement		1,700,000		1,700,000			1,700,000
Remaining transaction price		11,900,000		11,900,000			11,900,000
Remaining transaction price will be recorded in deferred revenue when invoiced		6,900,000		6,900,000			$ 6,900,000
Zai Lab [Member] | China License and Collaboration Agreement [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized		$ 400,000		$ 1,000,000

License and Collaboration Arr_5

License and Collaboration Arrangements - Additional Information 1 (Detail) - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2016	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Glaxo Smith Kline LLC [Member] | Respiratory Diseases Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research collaboration and license agreement entered month and year			2012-04
Extend research terms	3 months
Extend research date	2016-07
Glaxo Smith Kline LLC [Member] | Respiratory Diseases and Muscle Diseases Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Adjustments to transaction price		$ 0	$ 0
Milestone payment		0	0
Clinical and regulatory development milestone payments			$ 0
UCB Pharma S.A. [Member] | Fibrosis and CNS Collaboration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research collaboration and license agreement entered month and year			2013-03
Adjustments to transaction price		0	$ 0
Milestone payment		0	0
Clinical and regulatory development milestone payments			0
Transaction price			15,600,000	$ 15,600,000
Non-refundable up-front fee			6,000,000
Technology access fee			6,600,000
Research funding		$ 2,000,000	2,000,000
UCB Pharma S.A. [Member] | Fibrosis and CNS Collaboration [Member] | Reagent [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursements costs			$ 1,000,000

Leases - Additional Information

Leases - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)InstrumentTerm	Jan. 01, 2019USD ($)	Jul. 31, 2018
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. In October 2019, we commenced a corporate restructuring to extend our cash runway and ensure long-term sustainability. As part of the restructuring, we are initiating activities to reduce our corporate facilities footprint by either subletting a significant portion of our current leased space or subletting our current building and relocating to smaller facilities.
Operating lease cost	$ 1,500,000	$ 4,600,000
Variable lease cost	400,000	1,300,000
Cash paid for operating lease liabilities	$ 1,900,000	$ 4,900,000
Weighted-average discount rate, operating leases	7.00%	7.00%
Weighted-average remaining operating lease term	8 years	8 years
Bemarituzumab Programs [Member]
Lessee Lease Description [Line Items]
Lease term				3 years
Number of sequencing instruments | Instrument		4
Number of terms available | Term		2
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) $ in Thousands	Sep. 30, 2019USD ($)
Operating Lease Liabilities Payments Due [Abstract]
Remainder of 2019	$ 1,853
2020	7,564
2021	7,723
2022	7,799
2023	8,064
2024 and on	35,166
Total minimum lease payments	68,169
Less: amount of lease payments representing interest	(17,651)
Present value of future minimum lease payments	50,518
Less: operating lease obligations, current portion	(3,944)
Operating lease obligations, long-term portion	$ 46,574

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail) - Subsequent Event [Member] $ in Millions	1 Months Ended
	Oct. 31, 2019USD ($)Position
Subsequent Event [Line Items]
Percentage of company's workforce terminated	70.00%
Number of company's workforce terminated | Position	70
Pretax charges for severance and other personnel-related costs	$ 6
Pro-rated bonuses earned by and payable to each employee terminated in restructuring	$ 1.2
Percentage of bonus target amount applicable to terminated employee	100.00%
Retention bonuses for non-terminated employees	$ 2