Arcus Biosciences (RCUS) 10-Q 5 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 30, 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	RCUS
Entity Registrant Name	Arcus Biosciences, Inc.
Entity Central Index Key	0001724521
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38419
Entity Tax Identification Number	47-3898435
Entity Address, Address Line One	3928 Point Eden Way
Entity Address, City or Town	Hayward
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94545
City Area Code	510
Local Phone Number	694-6200
Entity Common Stock, Shares Outstanding		45,858,976
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, Par Value $0.0001 Per Share
Security Exchange Name	NYSE
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	[1]
Current assets:
Cash and cash equivalents	$ 78,992	$ 71,064
Short-term investments	111,997	185,480
Receivable from collaboration partners	5,276	0
Prepaid expenses and other current assets	4,223	2,321
Amounts owed by a related party	0	83
Total current assets	200,488	258,948
Long-term investments	5,992	3,181
Property and equipment, net	10,011	11,107
Equity investment in related party	0	1,202
Restricted cash	203	203
Other long-term assets	263	284
Total assets	216,957	274,925
Current liabilities
Accounts payable	2,905	3,102
Accrued liabilities	9,662	6,023
Deferred revenue, current	7,000	6,250
Other current liabilities	1,490	1,560
Total current liabilities	21,057	16,935
Deferred revenue, noncurrent	13,772	16,984
Deferred rent	3,875	4,272
Other long-term liabilities	1,026	1,792
Total liabilities	39,730	39,983
Stockholders’ equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of September 30, 2019 and December 31, 2018; no shares issued and outstanding as of September 30, 2019 and December 31, 2018	0	0
Common stock, $0.0001 par value, 400,000,000 shares authorized as of September 30, 2019 and December 31, 2018, respectively; 45,842,966 and 44,537,946 shares issued and outstanding as of September 30, 2019 and December 31, 2018 respectively	4	4
Additional paid-in capital	365,898	357,873
Accumulated deficit	(188,728)	(122,828)
Accumulated other comprehensive income (loss)	53	(107)
Total stockholders’ equity	177,227	234,942	[2]
Total liabilities, convertible preferred stock and stockholders’ equity	$ 216,957	$ 274,925
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.
[2]	The balances of December 31, 2018 and 2017 have been derived from the audited financial statements as of that date.

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	45,842,966	44,537,946
Common stock, shares outstanding	45,842,966	44,537,946

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Collaboration and license revenue	$ 1,750	$ 4,291	$ 5,250	$ 6,791
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operation expenses:
Research and development	$ 17,241	$ 12,859	$ 57,795	$ 38,210
General and administrative	7,758	3,577	18,637	9,956
Total operating expenses	24,999	16,436	76,432	48,166
Loss from operations	(23,249)	(12,145)	(71,182)	(41,375)
Non-operating income (expense):
Interest and other income, net	1,254	1,519	4,272	3,410
Gain on deemed sale from equity method investee	0	0	0	1,229
Share of loss from equity method investee	(357)	(186)	(1,202)	(563)
Total non-operating income, net	897	1,333	3,070	4,076
Net loss	(22,352)	(10,812)	(68,112)	(37,299)
Other comprehensive income (loss)	(59)	(25)	160	(66)
Comprehensive loss	$ (22,411)	$ (10,837)	$ (67,952)	$ (37,365)
Net loss per share, basic and diluted	$ (0.51)	$ (0.25)	$ (1.56)	$ (1.16)
Weighted-average number of shares used to compute basic and diluted net loss per share	43,939,281	42,838,098	43,750,154	32,056,675

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands		Total		Convertible Preferred Stock	Common Stock		Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Balance at Dec. 31, 2017	[1]	$ (72,328)					$ 948	$ (73,234)	$ (42)
Balance, shares at Dec. 31, 2017	[1]			30,459,574
Balance at Dec. 31, 2017	[1]			$ 226,196
Balance, shares at Dec. 31, 2017	[1]				3,278,129
Conversion of preferred stock to common stock		226,198			$ 3		226,195
Conversion of preferred stock to common stock				$ (226,196)
Conversion of preferred stock to common stock, shares					30,459,574
Issuance of common stock upon IPO		124,716			$ 1		124,715
Issuance of common stock upon IPO, shares					9,200,000
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares		80					80
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares					60,524
Vesting of early exercised stock options and restricted stock		278					278
Vesting of early exercised stock options and restricted stock, shares					129,152
Stock-based compensation		656					656
Other comprehensive income (loss)		(55)							(55)
Net loss		(12,955)						(12,955)
Balance at Mar. 31, 2018		266,590			$ 4		352,872	(86,189)	(97)
Balance, shares at Mar. 31, 2018				30,459,574
Balance, shares at Mar. 31, 2018					43,127,379
Balance at Dec. 31, 2017	[1]	$ (72,328)					948	(73,234)	(42)
Balance, shares at Dec. 31, 2017	[1]			30,459,574
Balance at Dec. 31, 2017	[1]			$ 226,196
Balance, shares at Dec. 31, 2017	[1]				3,278,129
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares		713,931
Net loss		$ (37,299)
Balance at Sep. 30, 2018		245,120			$ 4		355,758	(110,534)	(108)
Balance, shares at Sep. 30, 2018					43,405,673
Balance at Mar. 31, 2018		266,590			$ 4		352,872	(86,189)	(97)
Balance, shares at Mar. 31, 2018				30,459,574
Balance, shares at Mar. 31, 2018					43,127,379
Vesting of early exercised stock options and restricted stock		387					387
Vesting of early exercised stock options and restricted stock, shares					149,338
Stock-based compensation		1,116					1,116
Other comprehensive income (loss)		14							14
Net loss		(13,533)						(13,533)
Balance at Jun. 30, 2018		$ 254,574			$ 4		354,375	(99,722)	(83)
Balance, shares at Jun. 30, 2018					43,276,717
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares		0
Vesting of early exercised stock options and restricted stock		$ 335					335
Vesting of early exercised stock options and restricted stock, shares					128,956
Stock-based compensation		1,048					1,048
Other comprehensive income (loss)		(25)							(25)
Net loss		(10,812)						(10,812)
Balance at Sep. 30, 2018		245,120			$ 4		355,758	(110,534)	(108)
Balance, shares at Sep. 30, 2018					43,405,673
Balance at Dec. 31, 2018	[1]	$ 234,942	[2]		$ 4		357,873	(122,828)	(107)
Balance, shares at Dec. 31, 2018		44,537,946			43,610,823	[1]
Cumulative effect adjustment upon adoption of ASC 606 | ASC 606		$ 2,212						2,212
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares					69
Vesting of early exercised stock options and restricted stock		273					273
Vesting of early exercised stock options and restricted stock, shares					114,934
Stock-based compensation		1,674					1,674
Other comprehensive income (loss)		136							136
Net loss		(17,670)						(17,670)
Balance at Mar. 31, 2019		221,567			$ 4		359,820	(138,286)	29
Balance, shares at Mar. 31, 2019					43,725,826
Balance at Dec. 31, 2018	[1]	$ 234,942	[2]		$ 4		357,873	(122,828)	(107)
Balance, shares at Dec. 31, 2018		44,537,946			43,610,823	[1]
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares		18,770
Net loss		$ (68,112)
Balance at Sep. 30, 2019		$ 177,227			$ 4		365,898	(188,728)	53
Balance, shares at Sep. 30, 2019		45,842,966			44,035,557
Balance at Mar. 31, 2019		$ 221,567			$ 4		359,820	(138,286)	29
Balance, shares at Mar. 31, 2019					43,725,826
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares		99					99
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares					17,649
Vesting of early exercised stock options and restricted stock		260					260
Vesting of early exercised stock options and restricted stock, shares					107,952
Issuance of common stock under Employee Stock Purchase Plan		596					596
Issuance of common stock under Employee Stock Purchase Plan, shares					82,681
Stock-based compensation		2,130					2,130
Other comprehensive income (loss)		84							84
Net loss		(28,090)						(28,090)
Balance at Jun. 30, 2019		196,646			$ 4		362,905	(166,376)	113
Balance, shares at Jun. 30, 2019					43,934,108
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares		$ 1					1
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares		1,052			1,052
Vesting of early exercised stock options and restricted stock		$ 252					252
Vesting of early exercised stock options and restricted stock, shares					100,397
Stock-based compensation		2,740					2,740
Other comprehensive income (loss)		(60)							(60)
Net loss		(22,352)						(22,352)
Balance at Sep. 30, 2019		$ 177,227			$ 4		$ 365,898	$ (188,728)	$ 53
Balance, shares at Sep. 30, 2019		45,842,966			44,035,557
[1]	The balances of December 31, 2018 and 2017 have been derived from the audited financial statements as of that date.
[2]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flow from operating activities
Net loss	$ (68,112)	$ (37,299)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	6,544	2,820
Depreciation and amortization	2,722	2,717
Share of loss from equity method investee	1,202	563
Gain on deemed sale from equity method investee	0	(1,229)
Amortization of premiums on investments	(2,213)	(1,017)
Other non-operating income	0	(177)
Changes in operating assets and liabilities:
Receivable from collaboration partners	(5,276)	(5,000)
Amounts owed by a related party	83	(89)
Other long-term assets	21	0
Prepaid expenses and other current assets	(1,902)	(1,188)
Accounts payable	(94)	(1,029)
Accrued liabilities	3,639	4,141
Other current liabilities	42	33
Deferred revenue	(250)	1,209
Deferred rent	(397)	(344)
Net cash used in operating activities	(63,991)	(35,889)
Cash flow from investing activities
Purchases of short-term and long-term investments	(180,245)	(222,067)
Proceeds from maturities of short-term and long-term investments	253,290	109,601
Purchases of property and equipment	(1,729)	(3,485)
Net cash provided by (used in) investing activities	71,316	(115,951)
Cash flow from financing activities
Repurchase of unvested shares of stock	(94)	0
Proceeds from initial public offering, net of issuance costs	0	125,111
Proceeds from issuance of common stock upon exercise of stock options, net of repurchases	697	3,327
Payment of preferred stock issuance costs	0	(135)
Net cash provided by financing activities	603	128,303
Net increase (decrease) in cash and cash equivalents	7,928	(23,537)
Cash, cash equivalents and restricted cash at beginning of period	71,267	98,629
Cash, cash equivalents and restricted cash at end of period	79,195	75,092
Non-cash investing and financing activities:
Unpaid portion of property and equipment purchases included in accounts payable and accrued liabilities	33	103
Vesting of early exercised stock options and restricted stock	$ 784	$ 982

Organization

Organization	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	Note 1. Description of Business Arcus Biosciences, Inc. (Company or the Company) is a clinical-stage biopharmaceutical company focused on creating innovative cancer immunotherapies by leveraging underexploited biological opportunities. Specifically, the Company targets well-characterized biological pathways with significant scientific data supporting their importance in regulating the immune response against cancer and for which either there are no molecules in development or those that exist have suboptimal profiles. To exploit these pathways, the Company has built a robust and highly efficient discovery and clinical development capability to create and optimize highly differentiated small-molecule immuno-oncology product candidates. Since its inception in 2015, the Company has built a broad portfolio of small molecule and antibody product candidates that it plans to develop together as intra-portfolio combinations. Liquidity and Capital Resources As of September 30, 2019, the Company had cash and investments of $197.0 million, which are cash, cash equivalents, and investments in marketable securities that the Company believes will be sufficient to fund its planned operations for a period of at least twelve months following the filing date of this report.

Significant Accounting Policies

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Significant Accounting Policies	Note 2. Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the Company’s opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation of the results of operations and cash flows for the periods presented have been included. Operating results for the three and nine months ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019 or for any future period. The balance sheet as of December 31, 2018 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2018 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 5, 2019. From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s condensed consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the JOBS Act), the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. The Company will remain an emerging growth company until the earliest of (1) the last day of its first fiscal year (a) following the fifth anniversary of the completion of its initial public offering, (b) in which the Company has a total annual gross revenue of at least $1.07 billion, or (c) in which the Company is deemed to be a large accelerated filer, which means the market value of the common stock that is held by non-affiliates exceeds $700.0 million of the prior June 30th or (2) the date on which the Company has issued more than $1.0 billion in non-convertible debt securities during the prior three-year period. Principles of Consolidation During 2017, the Company established a wholly-owned subsidiary in Australia. The condensed consolidated financial statements include the Company’s accounts and those of its wholly-owned subsidiary. All intercompany accounts, transactions and balances have been eliminated. Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, as well as related disclosure of contingent assets and liabilities. Estimates were used to determine stock-based awards and other issuances, accruals for research and development costs, useful lives of long-lived assets, and uncertain tax positions. Actual results could differ materially from the Company’s estimates. Cash Equivalents, Short-Term and Long-Term Investments Cash equivalents include marketable securities having an original maturity of three months or less at the time of purchase. Short-term investments have maturities of greater than three months and up to twelve months at the time of purchase. Long-term investments have maturities greater than twelve months at the time of purchase. Collectively, cash equivalents, short-term and long-term investments are considered available-for-sale and are recorded at fair value. Unrealized gains and losses are recorded in accumulated other comprehensive loss. Realized gains and losses are included in interest and other income, net in the condensed consolidated statements of operations and comprehensive income or loss. The basis on which the cost of a security sold or amount reclassified out of accumulated other comprehensive income or loss into earnings is determined using the specific identification method. Restricted Cash Restricted cash at September 30, 2019 and December 31, 2018 comprises cash balances primarily held as security in connection with the Company’s facility lease agreements and is included in long-term assets in the condensed consolidated balance sheets. Concentration of Credit Risk Cash equivalents, short-term and long-term investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company invests in money market funds, treasury bills and notes, government bonds, commercial paper and corporate notes. The Company limits its credit risk associated with cash equivalents, short-term and long-term investments by placing them with banks and institutions it believes are credit worthy and in highly rated investments. Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist primarily of personnel costs for the Company’s research and development activities, non-personnel costs such as costs payable to third parties for preclinical and clinical studies and research services, laboratory supplies and equipment maintenance, product licenses, and other consulting costs. The Company estimates preclinical and clinical study and research expenses based on its knowledge of the services performed, pursuant to contracts with research institutions and other service providers that conduct and manage preclinical and clinical studies and research services on its behalf. The Company estimates these expenses based on discussions with internal management personnel and external service providers as to the progress or stage of completion of services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments associated with licensing agreements to acquire exclusive licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternative future use are expensed as incurred. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered. Adopted Accounting Pronouncements – Revenue Recognition Effective January 1, 2019, the Company adopted Accounting Standards Codification Topic 606, Revenue from Contracts with Customers The Company enters into collaborative arrangements with partners that fall under the scope of both ASC 606 and Accounting Standards Codification, Topic 808, Collaborative Arrangements As part of the accounting for these arrangements, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligations. The estimation of the stand-alone selling price may include such estimates as forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if they can be satisfied at a point in time or over time, and the Company measures the services delivered to the customer, which are periodically reviewed based on the progress of the related program. The effect of any change made to an estimated input component and, therefore revenue or expense recognized, would be recorded as a change in estimate. In addition, variable consideration (e.g. milestone payments) must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. Upfront Research and Development Fees: The Company identifies the performance obligations associated with the upfront research and development fees and determines if any of the promised services are distinct from each other. If a promised service is determined to be distinct, then the Company allocates the transaction price amongst the promised services based on its best judgment of their estimated stand-alone selling prices. If the promised services are not distinct, then all of the services are bundled together, and the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time. If the performance obligation is considered to be satisfied over time, the Company selects the revenue recognition method that it believes most faithfully depicts the Company’s performance in transferring control of the services. ASC 606 allows entities to choose between two methods to measure progress toward complete satisfaction of a performance obligation over time: input methods or output methods. Input methods recognize revenue on the basis of the entity’s efforts or inputs 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 to the satisfaction of that performance obligation. Output methods recognize revenue on the basis of direct measurements of the value to the customer of the goods or services transferred to date relative to the remaining goods or services promised under the contract (e.g. surveys of performance completed to date, appraisals of results achieved, milestones reached, time elapsed, and units produced or units delivered). The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Option Fees: At the inception of each arrangement that includes option exercise fees to obtain development and commercialization licenses for the Company’s products, the Company determines whether or not such option fee is considered a material right. If the option is considered a material right, then that option is considered a separate performance obligation in the contract and the transaction price includes the option fee in the allocation amongst the performance obligations. If the option is not considered a material right, then the option is accounted for as a separate contract. Milestone Payments: For arrangements that include development milestone payments, the Company consider the milestone payments to be variable consideration under ASC 606 at the inception of the arrangement, evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or the licensee’s control, such as regulatory approvals, are not considered probable of being earned until the uncertainty associated with the approvals has been resolved. The transaction price is then allocated to each performance obligation, on a relative standalone selling price basis, which the Company recognizes as revenue when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of earning such development milestones and any related constraint, and if necessary, adjusts the estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and earnings in the period of adjustment. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). Upfront payments and fees are recorded as deferred revenue when due and payable, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Impact of Adoption – ASC 606 The Company entered into a license and collaboration agreement (the Taiho Agreement) in September 2017, an agreement that is within the scope of ASC 606, under which it has provided Taiho Pharmaceutical Co., Ltd (Taiho) exclusive options, over a five-year period (the Option Period) to obtain an exclusive development and commercialization license to clinical stage product candidates from the Company’s programs. The terms of the arrangement include non-refundable upfront research and development fees, option fees to obtain development and commercialization licenses for the Company’s products, milestone payments based on achievement of defined development, regulatory and sales targets, and royalties on sales of commercialized product. The Company has applied the five-step model of the new standard to the Taiho Agreement, the only Company contract that has been impacted by the adoption of the new revenue standards. The Company implemented the new revenue standard using the modified retrospective transition method. Results for the three and nine months ended September 30, 2019 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with the Company’s historic accounting under previous revenue recognition guidance, Accounting Standards Codification Topic 605: Revenue Recognition (Topic 605). Upon the adoption, the Company recorded a net reduction of $2.2 million to its opening accumulated deficit as of January 1, 2019, due to the cumulative impact of adopting Topic 606, with the impact primarily relating to an increase in the transaction price recognized for the non-refundable upfront research and development fees over the five-year term. The impact of the adoption of Topic 606 on contract liabilities and accumulated deficit balances as of January 1, 2019 was as follows (in thousands): December 31, 2018 Adjustment Due to the Adoption of Topic 606 January 1, 2019 Current portion of deferred revenue $ 6,250 $ 750 $ 7,000 Long-term portion of deferred revenue 16,984 (2,962 ) 14,022 Accumulated deficit $ (122,828 ) $ 2,212 $ (120,616 ) The adjustments due to the adoption of Topic 606 primarily relate to an increase in the transaction price recognized for the non-refundable upfront research and development fees over the five-year term. Under Topic 606, the Company recognized as the transaction price the total amount that the Company expects to receive related to the non-refundable upfront fees. As of December 31, 2018, the Company had received $30.0 million of the $35.0 million in upfront fees, which consisted of payments of $25.0 million in 2017 at the inception of the contract and an anniversary payment of $5.0 million in 2018. Given both the history of successful collection of all payments due and payable to-date and the exercise of an option by Taiho in 2018 on one of the Company’s programs, the Company believes the remaining $5.0 million due in October 2019 will also be received. Under Topic 605, the Company recognized as the initial transaction price only the $25.0 million payment received in 2017. The additional $2.2 million recorded in the adoption adjustment and attributable as revenue through December 31, 2018 under Topic 606 resulted in both a lower accumulated deficit and a lower total amount of deferred revenue as of January 1, 2019. The impact of the adoption of Topic 606 on the Company’s Condensed Consolidated Balance Sheet and Statement of Operations as of and for the period ended September 30, 2019 was as follows (in thousands): As of September 30, 2019 As Reported Balances without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Current portion of deferred revenue $ 7,000 $ 7,917 $ (917 ) Long-term portion of deferred revenue 13,772 15,574 (1,802 ) Accumulated deficit $ — $ — $ (2,399 ) Three Months Ended September 30, 2019 As Reported Without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Collaboration revenues $ 1,750 $ 1,618 $ 132 Net loss (22,352 ) (22,484 ) $ 132 Net loss per share, basic and diluted $ (0.51 ) $ (0.51 ) $ — Nine Months Ended September 30, 2019 As Reported Without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Collaboration revenues $ 5,250 $ 4,743 $ 507 Net loss (68,112 ) (68,619 ) $ 507 Net loss per share, basic and diluted $ (1.56 ) $ (1.57 ) $ — Adopted Accounting Pronouncements – Others In November 2016, the FASB issued ASU No. 2016-18 (Topic 230), Restricted Cash, Statement of Cash Flows Impact of Adoption – ASU 2016-18 The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same such amount shown on the condensed consolidated statements of cash flows (in thousands): September 30, 2019 December 31, 2018 September 30, 2018 December 31, 2017 Cash and cash equivalents $ 78,992 $ 71,064 $ 74,889 $ 98,426 Restricted cash 203 203 203 203 Cash, cash equivalents and restricted cash $ 79,195 $ 71,267 $ 75,092 $ 98,629 In June 2018, the FASB issued ASU No. 2018-07 (Topic 718), Compensation – Stock Compensation Recently Issued Accounting Standards or Updates Not Yet Effective In January 2016, the FASB issued ASU No. 2016-01 (Subtopic 825-10), Financial Instruments In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases In August 2018, the FASB issued ASU No.2018-13 (Topic 820), Fair Value Measurement. In August 2018, the FASB issued ASU No.2018-15 (Subtopic 350-40), Intangible – Goodwill and Other – Internal-Use Software. In November 2018, the FASB issued ASU No. 2018-18 (Topic 808), Collaborative Arrangements

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 3. Fair Value Measurements Financial assets and liabilities are recorded at fair value. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value and expands disclosures regarding fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value as follows: Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2—Inputs (other than quoted market prices included in Level 1) are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life. Level 3—Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. During the periods presented, the Company has not changed the manner in which it values assets and liabilities that are measured at fair value. The Company recognizes transfers between levels of the fair value hierarchy as of the end of the reporting period. There were no transfers within the hierarchy as of September 30, 2019 and December 31, 2018. The following tables set forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): Fair Value Measurements at September 30, 2019 Total Level 1 Level 2 Level 3 Assets Money market funds $ 64,611 $ 64,611 $ — $ — Corporate securities and commercial paper 51,630 — 51,630 — U.S. government treasury and agency securities 80,740 — 80,740 — $ 196,981 $ 64,611 $ 132,370 $ — Fair Value Measurements at December 31, 2018 Total Level 1 Level 2 Level 3 Assets Money market funds $ 45,017 $ 45,017 $ — $ — U.S. government treasury and agency securities 103,940 — 103,940 — Corporate securities and commercial paper 110,768 — 110,768 — $ 259,725 $ 45,017 $ 214,708 $ — Classified as (with contractual maturities): September 30, 2019 December 31, 2018 Cash and Cash equivalents $ 78,992 $ 71,064 Short-term investments (due within one year) 111,997 185,480 Long-term investments (due between one and two years) 5,992 3,181 $ 196,981 $ 259,725 The investments are classified as available-for-sale marketable securities. At September 30, 2019 and December 31, 2018, the balance in the Company’s accumulated other comprehensive loss comprised activity related to the Company’s available-for-sale marketable securities. There were no realized gains or losses recognized on the sale or maturity of available-for-sale marketable securities as of September 30, 2019 and December 31, 2018, and as a result, the Company did not reclassify any amounts out of accumulated other comprehensive loss for the periods then ended. The Company has a limited number of available-for-sale marketable securities in loss positions as of September 30, 2019, which the Company does not intend to sell and has concluded it will not be required to sell before recovery of the amortized cost for the investment at maturity (in thousands). Fair Value Measurements at September 30, 2019 Amortized Cost Unrealized Gain Unrealized Loss Fair Value Money market funds $ 64,611 $ — $ — $ 64,611 Corporate securities and commercial paper 51,618 12 — 51,630 U.S. government treasury and agency securities 80,698 42 — 80,740 $ 196,927 $ 54 $ — $ 196,981 Fair Value Measurements at December 31, 2018 Amortized Cost Unrealized Gain Unrealized Loss Fair Value Money market funds $ 45,017 $ — $ — $ 45,017 U.S. government treasury and agency securities 103,957 — (17 ) 103,940 Corporate securities and commercial paper 110,859 — (91 ) 110,768 $ 259,833 $ — $ (108 ) $ 259,725

Equity Investment

Equity Investment	9 Months Ended
	Sep. 30, 2019
Inventory Disclosure [Abstract]
Equity Investment	Note 4: Equity Investment In 2016, the Company purchased approximately 3.6 million shares of common stock of PACT Pharma, Inc. (PACT Pharma), a privately funded, early-stage biopharmaceutical company focused on adoptive cell therapy and 1.0 million shares of Series A preferred stock. The Company determined the fair value of such investment to be insignificant to the Company’s 2016 financial statements given the start-up nature of operations of PACT Pharma, and it was recorded at a nominal amount. The Company also received certain warrants to purchase PACT Pharma common stock exercisable upon PACT Pharma’s achievement of certain valuation thresholds pursuant to a Master Services Agreement between the Company and PACT Pharma (the PACT Agreement), which agreement has since expired. The Company determined PACT Pharma to be a variable interest entity, and that the Company has a variable interest in PACT. However, because the Company is not the primary beneficiary of PACT Pharma, it is not consolidating the results of operations of PACT Pharma in its condensed consolidated financial statements. The Company’s investment in PACT Pharma is accounted for as an equity method investment, and as a result the Company records its share of PACT Pharma’s operating results in interest and other income, net, in its condensed consolidated statement of operations and comprehensive loss. During the three months ended September 30, 2019, the Company’s share of PACT Pharma’s losses exceeded the carrying amount of the equity investment. The Company has no obligation to provide cash financing to PACT Pharma and accordingly, no additional losses are being recorded beyond the carrying investment amount. For the three and nine months ended September 30, 2019 the Company recorded $0.4 million and $1.2 million, respectively, for its share of PACT Pharma’s operating losses. The unrecognized equity method losses in excess of the Company’s investment was $0.1 million as of September 30, 2019. For the three and nine months ended September 30, 2018, the Company recorded $0.2 million and $0.6 million, respectively, relating to its share of PACT Pharma’s operating losses. For the three and nine months ended September 30, 2019 and for the year ended December 31, 2018, the Company determined the fair value of the warrants to be insignificant to the condensed consolidated financial statements.

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Agreements	Note 5. License and Collaboration Agreements Taiho Pharmaceutical Co., Ltd In September 2017, the Company and Taiho entered into an option and license agreement (the Taiho Agreement) to collaborate on the potential development and commercialization of certain product candidates from the Company’s portfolio in Japan and certain other territories in Asia (excluding China) (the Taiho Territory). The Taiho Agreement provides Taiho with exclusive options, over a five-year period (the Option Period), to obtain an exclusive development and commercialization license to clinical stage product candidates from the Company’s programs (each, an Arcus Program). In consideration for the exclusive options and other rights contained in the Taiho Agreement, Taiho agreed to make non-refundable, non-creditable cash payments to the Company totaling $35.0 million, of which the Company received $25.0 million during 2017. An additional $5.0 million was received in October 2018 and the remaining $5.0 million was received in October 2019. In the event that the Company has not initiated IND enabling studies for at least five Arcus Programs prior to the expiration of the Option Period, Taiho may elect to extend the Option Period, up to a maximum of seven years for the Option Period, subject to an extension fee. If Taiho elects to exercise an option it will be obligated to make an exercise option payment for each option exercise of between $3.0 million to $15.0 million, dependent on the development stage of the applicable Arcus Program for which the option is exercised. In addition, the Taiho Agreement provides that the Company is eligible to receive additional clinical and regulatory milestones totaling up to $130.0 million per Arcus Program, and it will be eligible to receive contingent payments of up to $145.0 million per Arcus Program associated with the achievement of specified levels of Taiho net sales in the Taiho Territory. In addition, the Company will receive royalties ranging from high single-digits to mid-teens on net sales of licensed products in the Taiho Territory. Royalties will be payable on a licensed product-by-licensed product and country-by-country basis during the period of time commencing on the first commercial sale of a licensed product in a country and ending upon the later of: (a) ten (10) years from the date of first commercial sale of such licensed product in such country; and (b) expiration of the last-to-expire valid claim of the Company’s patents covering the manufacture, use or sale or exploitation of such licensed product in such country (the Royalty Term). The Company evaluated the Taiho Agreement under ASC 606 and determined that the current performance obligations consist of (1) the research and development services, in which the Company will use commercially reasonable efforts to initiate IND enabling studies for at least five Arcus Programs, as well as further develop such Arcus Programs during the term of the Agreement, and (2) the obligation to participate on the joint steering committee. These deliverables are non-contingent in nature. The Company determined that the obligation to participate in the joint steering committee does not have stand-alone value to Taiho because the committee’s primary purpose is to monitor and govern the research and development activities and, hence, it is inseparable from the research and development services. The Company’s assessment of the transaction price included an analysis of amounts it expected to receive, which at contract inception consisted of the upfront cash payment of $20.0 million due upon contract execution in September 2017, a $5.0 million payment due within 30 days of contract execution, an anniversary payment of $5.0 million due in 2018, and a final anniversary payment of $5.0 million due in 2019. All payments were made by Taiho as they became due and payable so given this successful collection history, the Company considers that the entire $35.0 million in non-refundable fees to be the initial transaction price. The Company determined that the combined performance obligation of the research and development services and the obligation to participate on the joint steering committee are satisfied over time. The Company uses a time-elapsed input method to measure progress toward satisfying its performance obligation, which is the method the Company believes most faithfully depicts the Company’s performance in transferring the promised services during the time period in which Taiho has access to the Company’s research and development activities . Accordingly, the transaction price of $35.0 million will be recognized using this input method over the estimated performance period of five years. The Company also concluded that, at the inception of the agreement, Taiho’s exclusive options are not considered material rights as the options do not contain a significant and incremental discount. The Company will therefore exclude the exclusive options from the initial transaction price and account for them as separate contracts. In 2018, Taiho exercised its option to the Company’s adenosine receptor antagonist program for a fee of $3.0 million, which was recognized by the Company as revenue during the year ended December 31, 2018 under both Topic 606 and Topic 605. Upon this option exercise, Taiho now has the sole responsibility for the development and commercialization of licensed products from within the program in the Taiho Territory. No options were exercised by Taiho during the nine months ended September 30, 2019. The Company also determined that the clinical and regulatory milestone payments under the Taiho Agreement are variable consideration under Topic 606 which need to be added to the transaction price when it is probable that a significant revenue reversal will not occur. Based on the nature of the clinical and regulatory milestones, such as the regulatory approvals which are not within the Company’s control, the Company will not consider achievement of such milestones to be probable until the uncertainty associated with the approvals has been resolved. When it is probable that a significant reversal of revenue will not occur, the milestone payment will be added to the transaction price, which will then be allocated to each performance obligation, on a relative standalone selling price basis, for which the Company recognizes revenue. The Company also considers the contingent payments due from Taiho upon the achievement of specified sales volumes to be similar to royalty payments. The Company considers the license to be the predominant item to which the royalties relate. The Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). As of September 30, 2019, no sales milestone or royalty revenue has been recognized. The Taiho Agreement shall remain in effect until (a) expiration of the last exercise period if Taiho has not exercised any of its exclusive options prior to such expiration or (b) if Taiho has exercised any of its exclusive options prior to the expiration of the applicable exercise period, expiry of all Royalty Terms for the licensed products, in each case subject to certain exceptions. During the three and nine months ended September 30, 2019, the Company recognized a total of $1.8 million and $5.3 million, respectively, of revenue under the Taiho Agreement in accordance with Topic 606, consisting of revenue recognized for the non-refundable upfront research and development fees. As of September 30, 2019, the Company recorded deferred revenue, current and deferred revenue, noncurrent of $7.0 million and $13.7 million, respectively, in its condensed consolidated balance sheet. Changes in Deferred Revenue Balances The Company recognized the following revenue as a result of changes in the deferred revenue balance during the period below (in thousands): Three months ended September 30, Nine months ended September 30, Revenue recognized in the period from: 2019 2019 Amounts included in deferred revenue at the beginning of the period $ 1,750 $ 5,250 Performance obligations satisfied in previous period $ — $ — WuXi Biologics License Agreement The Company entered into a license agreement (the WuXi Agreement) with WuXi Biologics (Cayman) Inc. (WuXi Biologics) in August 2017, as subsequently amended in June 2019, in which it obtained an exclusive license to develop, use, manufacture, and commercialize products including an anti-PD-1 antibody worldwide except for Greater China and Thailand. The Company paid upfront and milestone payments of $18.5 million during the second half of 2017 which were recorded within research and development expenses, as the products had not reached technological feasibility and did not have alternative future use. The Company made a milestone payment of $7.5 million in the three and nine months ended September 30, 2019 which was recorded within research and development expenses. No milestones payments were made during the three and nine months ended September 30, 2018. The WuXi Agreement also provides for clinical and regulatory milestone payments, commercialization milestone payments of up to $375.0 million, and tiered royalty payments to be made to WuXi Biologics that range from the high single-digits to low teens of net sales by the Company of licensed products. Abmuno License Agreement In December 2016, the Company entered into a license agreement (the Abmuno Agreement) with Abmuno Therapeutics LLC (Abmuno) in which it obtained a worldwide exclusive license to develop, use, manufacture, and commercialize products that include an anti-TIGIT antibody. No milestone payments were made during the three and nine months ended September 30, 2019. The Company made upfront and milestone payments of $2.0 million and $2.8 million for the three and nine months ended September 30, 2018, respectively, which were recorded within research and development expenses, as the products have not reached technological feasibility and do not have alternative future use and therefore were expensed as incurred. The Abmuno Agreement also provides for additional clinical, regulatory and commercialization milestone remaining payments of up to $101.0 million as of September 30, 2019. Strata Collaboration Agreement On April 30, 2019, the Company and Strata Oncology, Inc. (Strata) entered into a Co-Development and Collaboration Agreement (the Co-Development and Collaboration Agreement) to pursue a clinical development collaboration utilizing Strata’s precision drug development platform and proprietary biomarkers to evaluate AB122, the Company’s clinical-stage anti-PD-1 antibody, in patients in a tumor-agnostic fashion. Under the terms of the Co-Development and Collaboration Agreement, the parties will share a portion of development costs for the clinical collaboration. Strata is eligible to receive $2.5 million upon the achievement of a development milestone, as well as regulatory and commercial milestones of up to $125.0 million and up to double-digit royalties on U.S. net sales of AB122 in the biomarker-identified indication. As of September 30, 2019, the Company incurred expenses of $0.3 million net of development cost sharing that was recorded within research and development expenses. As further consideration in connection with the Co-Development and Collaboration Agreement, the Company issued to Strata 1,257,651 restricted shares of its common stock with an initial measured fair value of $15.0 million, which are subject to vesting based upon the achievement of specified regulatory milestones within certain timelines, unless such vesting is modified at the acquiror’s option pursuant to a change of control of the Company. Expense relating to the restricted shares subject to these milestones is recognized if it is considered probable that the associated shares will vest. The probability of achievement is assessed at the end of each quarterly period. As of September 30, 2019, the Company determined that none of the restricted shares were probable of vesting and, as a result, no compensation expense related to the restricted shares has been recognized to date.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	Note 6: Stock-Based Compensation In March 2018, the Company adopted the 2018 Equity Incentive Plan (2018 Plan). The 2018 Plan replaced the Company’s 2015 Stock Plan (2015 Plan) and 3,570,000 shares were reserved under the 2018 Plan, along with any shares remaining available for issuance under the Company’s 2015 Plan or outstanding awards under its 2015 Plan that subsequently expire, lapse unexercised or are forfeited to or repurchased by the Company. Total stock-based compensation expense was recognized in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Research and development 978 $ 638 2,693 $ 1,679 General and administrative 1,762 410 3,851 1,141 Total stock-based compensation $ 2,740 $ 1,048 $ 6,544 $ 2,820 The Company granted 300,846 and 3,388,496 stock options during the three and nine months ended September 30, 2019, respectively and 130,000 and 1,526,989 for the three and nine months ended September 30, 2018, respectively. These options had a weighted average grant-date fair value of $5.49 and $6.53 per share for the three and nine months ended September 30, 2019, respectively, and $9.10 and $7.45 for the three and nine months ended September 30,2018, respectively. Under the Company’s stock plans, 1,052 and 18,770 stock options were exercised during the three and nine months ended September 30, 2019, respectively, and zero and 713,931 for the three and nine months ended September 30, 2018, respectively. As a result of early exercises under the 2015 Plan, approximately 552,364 and 927,123 shares had not vested and were subject to repurchase as of September 30, 2019 and December 31, 2018, respectively. The Company treats cash received from the exercise of unvested options as a refundable deposit and classifies such amounts as a liability in its condensed consolidated balance sheets. As of September 30, 2019 and December 31, 2018, the Company included cash received from the early exercise of unvested options of $2.0 million and $2.8 million, in its other current and long-term liabilities, respectively based on the timing of their expected vesting. Amounts included in liabilities are transferred into common stock and additional paid-in capital as the shares vest, which is generally over a period of 48 months.

Condensed Consolidated Balanc_3

Condensed Consolidated Balance Sheet Components	9 Months Ended
	Sep. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Condensed Consolidated Balance Sheet Components	Note 7. Condensed Consolidated Balance Sheet Components Property and Equipment Property and equipment, net consisted of the following (in thousands): As of September 30, 2019 As of December 31, 2018 Scientific equipment $ 8,036 $ 6,628 Furniture and equipment 1,120 813 Capitalized software 146 146 Leasehold improvements 10,834 10,828 Construction in progress 240 335 Total 20,376 18,750 Less: Accumulated depreciation and amortization (10,365 ) (7,643 ) Property and equipment, net $ 10,011 $ 11,107 Depreciation and amortization expense was $0.8 million and $2.7 million for the three and nine months ended September 30, 2019, respectively and $0.9 million and $2.7 million for the three and nine months ended September 30, 2018, respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): As of September 30, 2019 As of December 31, 2018 Accrued personnel expenses $ 3,455 $ 2,833 Accrued research and development expenses 5,805 2,816 Professional fees 281 211 Other 121 163 Total $ 9,662 $ 6,023

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Loss per Share	Note 8. Net Loss per Share The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net loss $ (22,352 ) $ (10,812 ) $ (68,112 ) $ (37,299 ) Denominator: Weighted-average common shares outstanding 45,787,137 44,452,184 45,253,176 33,937,800 Less: weighted-average common shares subject to vesting (1,847,856 ) (1,614,086 ) (1,503,022 ) (1,881,125 ) Weighted-average common shares used to compute basic and diluted net loss per share 43,939,281 42,838,098 43,750,154 32,056,675 Net loss per share: basic and diluted $ (0.51 ) $ (0.25 ) $ (1.56 ) $ (1.16 ) The following outstanding potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: Nine Months Ended September 30, 2019 2018 Common stock options issued and outstanding 4,274,163 1,348,955 Unvested restricted common stock 1,257,651 462,963 Unvested early exercised common stock options 552,364 1,050,103 Total 6,084,178 2,862,021

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the Company’s opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation of the results of operations and cash flows for the periods presented have been included. Operating results for the three and nine months ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019 or for any future period. The balance sheet as of December 31, 2018 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2018 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 5, 2019. From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s condensed consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the JOBS Act), the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. The Company will remain an emerging growth company until the earliest of (1) the last day of its first fiscal year (a) following the fifth anniversary of the completion of its initial public offering, (b) in which the Company has a total annual gross revenue of at least $1.07 billion, or (c) in which the Company is deemed to be a large accelerated filer, which means the market value of the common stock that is held by non-affiliates exceeds $700.0 million of the prior June 30th or (2) the date on which the Company has issued more than $1.0 billion in non-convertible debt securities during the prior three-year period.
Principles of Consolidation	Principles of Consolidation During 2017, the Company established a wholly-owned subsidiary in Australia. The condensed consolidated financial statements include the Company’s accounts and those of its wholly-owned subsidiary. All intercompany accounts, transactions and balances have been eliminated.
Use of Estimates	Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, as well as related disclosure of contingent assets and liabilities. Estimates were used to determine stock-based awards and other issuances, accruals for research and development costs, useful lives of long-lived assets, and uncertain tax positions. Actual results could differ materially from the Company’s estimates.
Cash Equivalents, Short-Term and Long-Term Investments	Cash Equivalents, Short-Term and Long-Term Investments Cash equivalents include marketable securities having an original maturity of three months or less at the time of purchase. Short-term investments have maturities of greater than three months and up to twelve months at the time of purchase. Long-term investments have maturities greater than twelve months at the time of purchase. Collectively, cash equivalents, short-term and long-term investments are considered available-for-sale and are recorded at fair value. Unrealized gains and losses are recorded in accumulated other comprehensive loss. Realized gains and losses are included in interest and other income, net in the condensed consolidated statements of operations and comprehensive income or loss. The basis on which the cost of a security sold or amount reclassified out of accumulated other comprehensive income or loss into earnings is determined using the specific identification method.
Restricted Cash	Restricted Cash Restricted cash at September 30, 2019 and December 31, 2018 comprises cash balances primarily held as security in connection with the Company’s facility lease agreements and is included in long-term assets in the condensed consolidated balance sheets.
Concentration of Credit Risk	Concentration of Credit Risk Cash equivalents, short-term and long-term investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company invests in money market funds, treasury bills and notes, government bonds, commercial paper and corporate notes. The Company limits its credit risk associated with cash equivalents, short-term and long-term investments by placing them with banks and institutions it believes are credit worthy and in highly rated investments.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist primarily of personnel costs for the Company’s research and development activities, non-personnel costs such as costs payable to third parties for preclinical and clinical studies and research services, laboratory supplies and equipment maintenance, product licenses, and other consulting costs. The Company estimates preclinical and clinical study and research expenses based on its knowledge of the services performed, pursuant to contracts with research institutions and other service providers that conduct and manage preclinical and clinical studies and research services on its behalf. The Company estimates these expenses based on discussions with internal management personnel and external service providers as to the progress or stage of completion of services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments associated with licensing agreements to acquire exclusive licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternative future use are expensed as incurred. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered.
Adopted Accounting Pronouncements	Adopted Accounting Pronouncements – Revenue Recognition Effective January 1, 2019, the Company adopted Accounting Standards Codification Topic 606, Revenue from Contracts with Customers The Company enters into collaborative arrangements with partners that fall under the scope of both ASC 606 and Accounting Standards Codification, Topic 808, Collaborative Arrangements As part of the accounting for these arrangements, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligations. The estimation of the stand-alone selling price may include such estimates as forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if they can be satisfied at a point in time or over time, and the Company measures the services delivered to the customer, which are periodically reviewed based on the progress of the related program. The effect of any change made to an estimated input component and, therefore revenue or expense recognized, would be recorded as a change in estimate. In addition, variable consideration (e.g. milestone payments) must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. Upfront Research and Development Fees: The Company identifies the performance obligations associated with the upfront research and development fees and determines if any of the promised services are distinct from each other. If a promised service is determined to be distinct, then the Company allocates the transaction price amongst the promised services based on its best judgment of their estimated stand-alone selling prices. If the promised services are not distinct, then all of the services are bundled together, and the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time. If the performance obligation is considered to be satisfied over time, the Company selects the revenue recognition method that it believes most faithfully depicts the Company’s performance in transferring control of the services. ASC 606 allows entities to choose between two methods to measure progress toward complete satisfaction of a performance obligation over time: input methods or output methods. Input methods recognize revenue on the basis of the entity’s efforts or inputs 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 to the satisfaction of that performance obligation. Output methods recognize revenue on the basis of direct measurements of the value to the customer of the goods or services transferred to date relative to the remaining goods or services promised under the contract (e.g. surveys of performance completed to date, appraisals of results achieved, milestones reached, time elapsed, and units produced or units delivered). The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Option Fees: At the inception of each arrangement that includes option exercise fees to obtain development and commercialization licenses for the Company’s products, the Company determines whether or not such option fee is considered a material right. If the option is considered a material right, then that option is considered a separate performance obligation in the contract and the transaction price includes the option fee in the allocation amongst the performance obligations. If the option is not considered a material right, then the option is accounted for as a separate contract. Milestone Payments: For arrangements that include development milestone payments, the Company consider the milestone payments to be variable consideration under ASC 606 at the inception of the arrangement, evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or the licensee’s control, such as regulatory approvals, are not considered probable of being earned until the uncertainty associated with the approvals has been resolved. The transaction price is then allocated to each performance obligation, on a relative standalone selling price basis, which the Company recognizes as revenue when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of earning such development milestones and any related constraint, and if necessary, adjusts the estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and earnings in the period of adjustment. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). Upfront payments and fees are recorded as deferred revenue when due and payable, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Impact of Adoption – ASC 606 The Company entered into a license and collaboration agreement (the Taiho Agreement) in September 2017, an agreement that is within the scope of ASC 606, under which it has provided Taiho Pharmaceutical Co., Ltd (Taiho) exclusive options, over a five-year period (the Option Period) to obtain an exclusive development and commercialization license to clinical stage product candidates from the Company’s programs. The terms of the arrangement include non-refundable upfront research and development fees, option fees to obtain development and commercialization licenses for the Company’s products, milestone payments based on achievement of defined development, regulatory and sales targets, and royalties on sales of commercialized product. The Company has applied the five-step model of the new standard to the Taiho Agreement, the only Company contract that has been impacted by the adoption of the new revenue standards. The Company implemented the new revenue standard using the modified retrospective transition method. Results for the three and nine months ended September 30, 2019 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with the Company’s historic accounting under previous revenue recognition guidance, Accounting Standards Codification Topic 605: Revenue Recognition (Topic 605). Upon the adoption, the Company recorded a net reduction of $2.2 million to its opening accumulated deficit as of January 1, 2019, due to the cumulative impact of adopting Topic 606, with the impact primarily relating to an increase in the transaction price recognized for the non-refundable upfront research and development fees over the five-year term. The impact of the adoption of Topic 606 on contract liabilities and accumulated deficit balances as of January 1, 2019 was as follows (in thousands): December 31, 2018 Adjustment Due to the Adoption of Topic 606 January 1, 2019 Current portion of deferred revenue $ 6,250 $ 750 $ 7,000 Long-term portion of deferred revenue 16,984 (2,962 ) 14,022 Accumulated deficit $ (122,828 ) $ 2,212 $ (120,616 ) The adjustments due to the adoption of Topic 606 primarily relate to an increase in the transaction price recognized for the non-refundable upfront research and development fees over the five-year term. Under Topic 606, the Company recognized as the transaction price the total amount that the Company expects to receive related to the non-refundable upfront fees. As of December 31, 2018, the Company had received $30.0 million of the $35.0 million in upfront fees, which consisted of payments of $25.0 million in 2017 at the inception of the contract and an anniversary payment of $5.0 million in 2018. Given both the history of successful collection of all payments due and payable to-date and the exercise of an option by Taiho in 2018 on one of the Company’s programs, the Company believes the remaining $5.0 million due in October 2019 will also be received. Under Topic 605, the Company recognized as the initial transaction price only the $25.0 million payment received in 2017. The additional $2.2 million recorded in the adoption adjustment and attributable as revenue through December 31, 2018 under Topic 606 resulted in both a lower accumulated deficit and a lower total amount of deferred revenue as of January 1, 2019. The impact of the adoption of Topic 606 on the Company’s Condensed Consolidated Balance Sheet and Statement of Operations as of and for the period ended September 30, 2019 was as follows (in thousands): As of September 30, 2019 As Reported Balances without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Current portion of deferred revenue $ 7,000 $ 7,917 $ (917 ) Long-term portion of deferred revenue 13,772 15,574 (1,802 ) Accumulated deficit $ — $ — $ (2,399 ) Three Months Ended September 30, 2019 As Reported Without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Collaboration revenues $ 1,750 $ 1,618 $ 132 Net loss (22,352 ) (22,484 ) $ 132 Net loss per share, basic and diluted $ (0.51 ) $ (0.51 ) $ — Nine Months Ended September 30, 2019 As Reported Without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Collaboration revenues $ 5,250 $ 4,743 $ 507 Net loss (68,112 ) (68,619 ) $ 507 Net loss per share, basic and diluted $ (1.56 ) $ (1.57 ) $ — Adopted Accounting Pronouncements – Others In November 2016, the FASB issued ASU No. 2016-18 (Topic 230), Restricted Cash, Statement of Cash Flows Impact of Adoption – ASU 2016-18 The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same such amount shown on the condensed consolidated statements of cash flows (in thousands): September 30, 2019 December 31, 2018 September 30, 2018 December 31, 2017 Cash and cash equivalents $ 78,992 $ 71,064 $ 74,889 $ 98,426 Restricted cash 203 203 203 203 Cash, cash equivalents and restricted cash $ 79,195 $ 71,267 $ 75,092 $ 98,629 In June 2018, the FASB issued ASU No. 2018-07 (Topic 718), Compensation – Stock Compensation
Recently Issued Accounting Standards or Updates Not Yet Effective	Recently Issued Accounting Standards or Updates Not Yet Effective In January 2016, the FASB issued ASU No. 2016-01 (Subtopic 825-10), Financial Instruments In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases In August 2018, the FASB issued ASU No.2018-13 (Topic 820), Fair Value Measurement. In August 2018, the FASB issued ASU No.2018-15 (Subtopic 350-40), Intangible – Goodwill and Other – Internal-Use Software. In November 2018, the FASB issued ASU No. 2018-18 (Topic 808), Collaborative Arrangements

Summary of Significant Accounti

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
ASC 606
Significant Accounting Policies [Line Items]
Impact of Adoption	The impact of the adoption of Topic 606 on contract liabilities and accumulated deficit balances as of January 1, 2019 was as follows (in thousands): December 31, 2018 Adjustment Due to the Adoption of Topic 606 January 1, 2019 Current portion of deferred revenue $ 6,250 $ 750 $ 7,000 Long-term portion of deferred revenue 16,984 (2,962 ) 14,022 Accumulated deficit $ (122,828 ) $ 2,212 $ (120,616 ) The impact of the adoption of Topic 606 on the Company’s Condensed Consolidated Balance Sheet and Statement of Operations as of and for the period ended September 30, 2019 was as follows (in thousands): As of September 30, 2019 As Reported Balances without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Current portion of deferred revenue $ 7,000 $ 7,917 $ (917 ) Long-term portion of deferred revenue 13,772 15,574 (1,802 ) Accumulated deficit $ — $ — $ (2,399 ) Three Months Ended September 30, 2019 As Reported Without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Collaboration revenues $ 1,750 $ 1,618 $ 132 Net loss (22,352 ) (22,484 ) $ 132 Net loss per share, basic and diluted $ (0.51 ) $ (0.51 ) $ — Nine Months Ended September 30, 2019 As Reported Without the Adoption of Topic 606 Effect of Adoption Higher/ (Lower) Collaboration revenues $ 5,250 $ 4,743 $ 507 Net loss (68,112 ) (68,619 ) $ 507 Net loss per share, basic and diluted $ (1.56 ) $ (1.57 ) $ —
ASU 2016-18
Significant Accounting Policies [Line Items]
Impact of Adoption	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same such amount shown on the condensed consolidated statements of cash flows (in thousands): September 30, 2019 December 31, 2018 September 30, 2018 December 31, 2017 Cash and cash equivalents $ 78,992 $ 71,064 $ 74,889 $ 98,426 Restricted cash 203 203 203 203 Cash, cash equivalents and restricted cash $ 79,195 $ 71,267 $ 75,092 $ 98,629

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets Measured on Recurring Basis	The following tables set forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): Fair Value Measurements at September 30, 2019 Total Level 1 Level 2 Level 3 Assets Money market funds $ 64,611 $ 64,611 $ — $ — Corporate securities and commercial paper 51,630 — 51,630 — U.S. government treasury and agency securities 80,740 — 80,740 — $ 196,981 $ 64,611 $ 132,370 $ — Fair Value Measurements at December 31, 2018 Total Level 1 Level 2 Level 3 Assets Money market funds $ 45,017 $ 45,017 $ — $ — U.S. government treasury and agency securities 103,940 — 103,940 — Corporate securities and commercial paper 110,768 — 110,768 — $ 259,725 $ 45,017 $ 214,708 $ —
Schedule of Investments Classified as Available for Sale Securities with Contractual Maturities	Classified as (with contractual maturities): September 30, 2019 December 31, 2018 Cash and Cash equivalents $ 78,992 $ 71,064 Short-term investments (due within one year) 111,997 185,480 Long-term investments (due between one and two years) 5,992 3,181 $ 196,981 $ 259,725
Schedule of Available for Sale Securities at Fair Value Measurements	Fair Value Measurements at September 30, 2019 Amortized Cost Unrealized Gain Unrealized Loss Fair Value Money market funds $ 64,611 $ — $ — $ 64,611 Corporate securities and commercial paper 51,618 12 — 51,630 U.S. government treasury and agency securities 80,698 42 — 80,740 $ 196,927 $ 54 $ — $ 196,981 Fair Value Measurements at December 31, 2018 Amortized Cost Unrealized Gain Unrealized Loss Fair Value Money market funds $ 45,017 $ — $ — $ 45,017 U.S. government treasury and agency securities 103,957 — (17 ) 103,940 Corporate securities and commercial paper 110,859 — (91 ) 110,768 $ 259,833 $ — $ (108 ) $ 259,725

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	9 Months Ended
	Sep. 30, 2019
License And Collaboration Agreements [Abstract]
Summary of Revenue Recognized as a Result of Changes in Deferred Revenue	The Company recognized the following revenue as a result of changes in the deferred revenue balance during the period below (in thousands): Three months ended September 30, Nine months ended September 30, Revenue recognized in the period from: 2019 2019 Amounts included in deferred revenue at the beginning of the period $ 1,750 $ 5,250 Performance obligations satisfied in previous period $ — $ —

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-Based Compensation Expense	Total stock-based compensation expense was recognized in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Research and development 978 $ 638 2,693 $ 1,679 General and administrative 1,762 410 3,851 1,141 Total stock-based compensation $ 2,740 $ 1,048 $ 6,544 $ 2,820

Condensed Consolidated Balanc_4

Condensed Consolidated Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): As of September 30, 2019 As of December 31, 2018 Scientific equipment $ 8,036 $ 6,628 Furniture and equipment 1,120 813 Capitalized software 146 146 Leasehold improvements 10,834 10,828 Construction in progress 240 335 Total 20,376 18,750 Less: Accumulated depreciation and amortization (10,365 ) (7,643 ) Property and equipment, net $ 10,011 $ 11,107
Summary of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): As of September 30, 2019 As of December 31, 2018 Accrued personnel expenses $ 3,455 $ 2,833 Accrued research and development expenses 5,805 2,816 Professional fees 281 211 Other 121 163 Total $ 9,662 $ 6,023

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss Per Share	The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net loss $ (22,352 ) $ (10,812 ) $ (68,112 ) $ (37,299 ) Denominator: Weighted-average common shares outstanding 45,787,137 44,452,184 45,253,176 33,937,800 Less: weighted-average common shares subject to vesting (1,847,856 ) (1,614,086 ) (1,503,022 ) (1,881,125 ) Weighted-average common shares used to compute basic and diluted net loss per share 43,939,281 42,838,098 43,750,154 32,056,675 Net loss per share: basic and diluted $ (0.51 ) $ (0.25 ) $ (1.56 ) $ (1.16 )
Summary of Outstanding Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss per Share	The following outstanding potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: Nine Months Ended September 30, 2019 2018 Common stock options issued and outstanding 4,274,163 1,348,955 Unvested restricted common stock 1,257,651 462,963 Unvested early exercised common stock options 552,364 1,050,103 Total 6,084,178 2,862,021

Organization - Additional Infor

Organization - Additional Information (Details) $ in Millions	Sep. 30, 2019USD ($)
Cash, Cash Equivalents and Investments in Marketable Securities
Class Of Stock [Line Items]
Cash and investments	$ 197

Significant Accounting Polici_3

Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended			9 Months Ended	12 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2017	Sep. 30, 2019	Dec. 31, 2018		Dec. 31, 2017	Jan. 01, 2019	Jun. 29, 2017
Significant Accounting Policies [Line Items]
Description to be remained in emerging growth company				The Company will remain an emerging growth company until the earliest of (1) the last day of its first fiscal year (a) following the fifth anniversary of the completion of its initial public offering, (b) in which the Company has a total annual gross revenue of at least $1.07 billion, or (c) in which the Company is deemed to be a large accelerated filer, which means the market value of the common stock that is held by non-affiliates exceeds $700.0 million of the prior June 30th or (2) the date on which the Company has issued more than $1.0 billion in non-convertible debt securities during the prior three-year period.
Minimum annual gross revenue in order to remain classified as emerging growth company				$ 1,070,000
Maximum market value of common stock held by non-affiliates to be remained in emerging growth company									$ 700,000
Additional non-convertible debt securities to be remained in emerging growth company				1,000,000
Accumulated deficit				(188,728)	$ (122,828)	[1]
Taiho Pharmaceutical Co Ltd | Taiho Agreement
Significant Accounting Policies [Line Items]
Non-refundable, non-creditable upfront cash payments				35,000
Payment received for license agreement		$ 5,000	$ 5,000	$ 5,000	5,000		$ 25,000
Taiho Pharmaceutical Co Ltd | Taiho Agreement | Subsequent Event
Significant Accounting Policies [Line Items]
Payment received for license agreement	$ 5,000
ASC 606
Significant Accounting Policies [Line Items]
Accumulated deficit								$ (120,616)
Non-refundable upfront research and development fees term				5 years
ASC 606 | Taiho Pharmaceutical Co Ltd | Taiho Agreement
Significant Accounting Policies [Line Items]
Accumulated deficit					2,200
Non-refundable upfront research and development fees term				5 years
Non refundable and non creditable upfront cash payment received					30,000
Non-refundable, non-creditable upfront cash payments				$ 35,000
Payment received for license agreement							$ 25,000
Additional payment to be received for license agreement					5,000
Net reduction to deferred revenue					$ 2,200
ASC 606 | Taiho Pharmaceutical Co Ltd | Taiho Agreement | Subsequent Event
Significant Accounting Policies [Line Items]
Remaining non refundable and non creditable cash payments receivable	$ 5,000
ASC 606 | Adjustment due to The Adoption of Topic 606
Significant Accounting Policies [Line Items]
Accumulated deficit								$ 2,212
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Significant Accounting Polici_4

Significant Accounting Policies - Summary of Impact of Adoption of Topic 606 on Contract Liabilities and Accumulated Deficit (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Current portion of deferred revenue	$ 7,000
Long-term portion of deferred revenue	13,772
Accumulated deficit	(188,728)		$ (122,828)	[1]
Before Adoption of Topic 606
Significant Accounting Policies [Line Items]
Current portion of deferred revenue	7,917		6,250
Long-term portion of deferred revenue	$ 15,574		16,984
Accumulated deficit			$ (122,828)
ASC 606
Significant Accounting Policies [Line Items]
Current portion of deferred revenue		$ 7,000
Long-term portion of deferred revenue		14,022
Accumulated deficit		(120,616)
ASC 606 | Adjustment due to The Adoption of Topic 606
Significant Accounting Policies [Line Items]
Current portion of deferred revenue		750
Long-term portion of deferred revenue		(2,962)
Accumulated deficit		$ 2,212
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Significant Accounting Polici_5

Significant Accounting Policies - Summary of Impact of Adoption of Topic 606 on Condensed Consolidated Balance Sheet and Statement of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Current portion of deferred revenue	$ 7,000						$ 7,000
Long-term portion of deferred revenue	13,772						13,772
Accumulated deficit	(188,728)						(188,728)			$ (122,828)	[1]
Collaboration revenues	1,750						5,250
Net loss	$ (22,352)	$ (28,090)	$ (17,670)	$ (10,812)	$ (13,533)	$ (12,955)	$ (68,112)	$ (37,299)
Net loss per share, basic and diluted	$ (0.51)			$ (0.25)			$ (1.56)	$ (1.16)
Balances Without the Adoption of Topic 606
Significant Accounting Policies [Line Items]
Current portion of deferred revenue	$ 7,917						$ 7,917			6,250
Long-term portion of deferred revenue	15,574						15,574			16,984
Accumulated deficit										$ (122,828)
Collaboration revenues	1,618						4,743
Net loss	$ (22,484)						$ (68,619)
Net loss per share, basic and diluted	$ (0.51)						$ (1.57)
ASC 606
Significant Accounting Policies [Line Items]
Current portion of deferred revenue									$ 7,000
Long-term portion of deferred revenue									14,022
Accumulated deficit									$ (120,616)
ASC 606 | Effect of Adoption Higher/ (Lower)
Significant Accounting Policies [Line Items]
Current portion of deferred revenue	$ (917)						$ (917)
Long-term portion of deferred revenue	(1,802)						(1,802)
Accumulated deficit	(2,399)						(2,399)
Collaboration revenues	132						507
Net loss	$ 132						$ 507
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Significant Accounting Polici_6

Significant Accounting Policies - Summary of Cash After Implementing ASU 2016-18 (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018		Sep. 30, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 78,992	$ 71,064	[1]
Restricted cash	203	203	[1]
ASU 2016-18
Significant Accounting Policies [Line Items]
Cash and cash equivalents	78,992	71,064		$ 74,889	$ 98,426
Restricted cash	203	203		203	203
Cash, cash equivalents and restricted cash	$ 79,195	$ 71,267		$ 75,092	$ 98,629
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair value assets transferred from level 1 to level 2	$ 0	$ 0
Fair value assets transferred from level 2 to level 1	0	0
Fair value liabilities transferred from level 1 to level 2	0	0
Fair value liabilities transferred from level 2 to level 1	0	0
Fair value assets transferred into level 3	0	0
Fair value assets transferred out of level 3	0	0
Fair value liabilities transferred into level 3	0	0
Fair value liabilities transferred out of level 3	0	0
Realized gains (loss) on sale or maturity of available-for-sale marketable securities	0	0
Reclassification out of accumulated other comprehensive loss	$ 0	$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value, Assets Measured on Recurring Basis (Details) - Fair Value On Recurring Basis - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	$ 196,981	$ 259,725
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	64,611	45,017
Corporate Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	51,630	110,768
U.S. Government Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	80,740	103,940
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	64,611	45,017
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	64,611	45,017
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	132,370	214,708
Level 2 | Corporate Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	51,630	110,768
Level 2 | U.S. Government Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	$ 80,740	$ 103,940

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Investments Classified as Available for Sale Securities with Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Cash and Cash equivalents	$ 78,992	$ 71,064
Short-term investments (due within one year)	111,997	185,480	[1]
Long-term investments (due between one and two years)	5,992	3,181	[1]
Total cash and investments in marketable securities	$ 196,981	$ 259,725
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Fair Value Measurements - Sch_3

Fair Value Measurements - Schedule of Available for Sale Securities at Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 196,927	$ 259,833
Unrealized Gain	54
Unrealized Loss		(108)
Fair Value	196,981	259,725
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	64,611	45,017
Fair Value	64,611	45,017
Corporate Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	51,618	110,859
Unrealized Gain	12
Unrealized Loss		(91)
Fair Value	51,630	110,768
U.S. Government Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	80,698	103,957
Unrealized Gain	42
Unrealized Loss		(17)
Fair Value	$ 80,740	$ 103,940

Equity Investment - Additional

Equity Investment - Additional Information (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Loss from equity method investments	$ 357	$ 186	$ 1,202	$ 563
PACT Pharma
Schedule of Equity Method Investments [Line Items]
Loss from equity method investments	$ 400	$ 200	1,200	$ 600
Unrealized loss on equity method investments			$ 100
PACT Pharma | Series A Preferred Stock
Schedule of Equity Method Investments [Line Items]
Purchase of common stock, shares					1
PACT Pharma | Common Stock
Schedule of Equity Method Investments [Line Items]
Purchase of common stock, shares					3.6

License and Collaboration Agr_3

License and Collaboration Agreements - Additional Information (Details)

Apr. 30, 2019USD ($)shares

Oct. 31, 2019USD ($)

Oct. 31, 2018USD ($)

Oct. 31, 2017USD ($)

Sep. 30, 2017USD ($)Program

Aug. 31, 2017USD ($)

Sep. 30, 2019USD ($)shares

Sep. 30, 2018USD ($)shares

Dec. 31, 2017USD ($)

Sep. 30, 2019USD ($)shares

Sep. 30, 2018USD ($)shares

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

License And Collaboration Agreements [Line Items]

Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares | shares

1,052

0

18,770

713,931

Revenue recognized

$ 1,750,000

$ 5,250,000

Deferred revenue, current

7,000,000

7,000,000

$ 6,250,000

[1]

Deferred revenue, noncurrent

13,772,000

13,772,000

16,984,000

[1]

Compensation expense recognized

2,740,000

$ 1,048,000

6,544,000

$ 2,820,000

Research and Development Expenses

License And Collaboration Agreements [Line Items]

Compensation expense recognized

978,000

638,000

2,693,000

1,679,000

Taiho Pharmaceutical Co Ltd | Taiho Agreement

License And Collaboration Agreements [Line Items]

Option period

5 years

Non refundable and non creditable cash payments

$ 35,000,000

Payment received for license agreement

$ 5,000,000

$ 5,000,000

$ 5,000,000

5,000,000

$ 25,000,000

Range of royalties receivable on net sales

high single-digits to mid-teens

Royalties payable description

Royalties will be payable on a licensed product-by-licensed product and country-by-country basis during the period of time commencing on the first commercial sale of a licensed product in a country and ending upon the later of: (a) ten (10) years from the date of first commercial sale of such licensed product in such country; and (b) expiration of the last-to-expire valid claim of the Company’s patents covering the manufacture, use or sale or exploitation of such licensed product in such country (the Royalty Term).

Upfront cash payment

$ 20,000,000

Non-refundable, non-creditable upfront cash payments

$ 35,000,000

Estimated performance period

5 years

Payment for first option exercise

$ 3,000,000

Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares | shares

0

Clinical and regulatory milestones achieved

$ 0

Sales milestone or royalty revenue recognized

0

Revenue recognized

1,800,000

5,300,000

Deferred revenue, current

7,000,000

7,000,000

Deferred revenue, noncurrent

13,700,000

$ 13,700,000

Taiho Pharmaceutical Co Ltd | Taiho Agreement | Subsequent Event

License And Collaboration Agreements [Line Items]

Payment received for license agreement

$ 5,000,000

Taiho Pharmaceutical Co Ltd | Taiho Agreement | Minimum

License And Collaboration Agreements [Line Items]

Number of programs, IND enabling studies not initiated | Program

5

Payment for option exercise

$ 3,000,000

Taiho Pharmaceutical Co Ltd | Taiho Agreement | Maximum

License And Collaboration Agreements [Line Items]

Extended option agreement period

7 years

Payment for option exercise

$ 15,000,000

Additional clinical and regulatory milestone payments receivable

130,000,000

Contingent payments receivable

$ 145,000,000

WuXi Biologics License Agreement

License And Collaboration Agreements [Line Items]

Upfront and milestone payments

$ 18,500,000

Range of tiered royalty payments on net sales

high single-digits to low teens

WuXi Biologics License Agreement | Research and Development Expenses

License And Collaboration Agreements [Line Items]

Milestone payments

7,500,000

0

$ 7,500,000

0

WuXi Biologics License Agreement | Maximum

License And Collaboration Agreements [Line Items]

Clinical, regulatory and commercialization milestone payments

$ 375,000,000

Abmuno License Agreement

License And Collaboration Agreements [Line Items]

Milestone payments

$ 0

0

Abmuno License Agreement | Research and Development Expenses

License And Collaboration Agreements [Line Items]

Upfront and milestone payments

$ 2,000,000

$ 2,800,000

Abmuno License Agreement | Maximum

License And Collaboration Agreements [Line Items]

Clinical, regulatory and commercialization remaining milestone payments

101,000,000

Strata Oncology Inc | Co-Development and Collaboration Agreement

License And Collaboration Agreements [Line Items]

Development milestone payable

$ 2,500,000

Development cost recorded within research and development expenses

$ 300,000

Number of restricted shares of common stock issued | shares

1,257,651

Fair value of restricted shares of common stock issued

$ 15,000,000

Strata Oncology Inc | Co-Development and Collaboration Agreement | Restricted Shares

License And Collaboration Agreements [Line Items]

Shares probable of vesting | shares

0

0

Compensation expense recognized

$ 0

Strata Oncology Inc | Co-Development and Collaboration Agreement | Maximum

License And Collaboration Agreements [Line Items]

Regulatory and commercial milestone payable

$ 125,000,000

[1]

The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

License and Collaboration Agr_4

License and Collaboration Agreements - Summary of Revenue Recognized as a Result of Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
License And Collaboration Agreements [Abstract]
Amounts included in deferred revenue at the beginning of the period	$ 1,750	$ 5,250

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, grants in period, shares	300,846	130,000	3,388,496	1,526,989
Stock options, grants in period, weighted average grant date fair value per share	$ 5.49	$ 9.10	$ 6.53	$ 7.45
Stock options, exercised	1,052	0	18,770	713,931
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued or transferred						3,570,000
2015 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares not vested and subject to repurchase	552,364		552,364		927,123
Cash received from early exercise of unvested options	$ 2		$ 2		$ 2.8
Award vesting period			48 months

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - 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]
Total stock-based compensation	$ 2,740	$ 1,048	$ 6,544	$ 2,820
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	978	638	2,693	1,679
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,762	$ 410	$ 3,851	$ 1,141

Condensed Consolidated Balanc_5

Condensed Consolidated Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total	$ 20,376	$ 18,750
Less: Accumulated depreciation and amortization	(10,365)	(7,643)
Property and equipment, net	10,011	11,107	[1]
Scientific Equipment
Property Plant And Equipment [Line Items]
Total	8,036	6,628
Furniture and Equipment
Property Plant And Equipment [Line Items]
Total	1,120	813
Capitalized Software
Property Plant And Equipment [Line Items]
Total	146	146
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total	10,834	10,828
Construction in Progress
Property Plant And Equipment [Line Items]
Total	$ 240	$ 335
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Condensed Consolidated Balanc_6

Condensed Consolidated Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation and amortization	$ 800	$ 900	$ 2,722	$ 2,717

Condensed Consolidated Balanc_7

Condensed Consolidated Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Accrued personnel expenses	$ 3,455	$ 2,833
Accrued research and development expenses	5,805	2,816
Professional fees	281	211
Other	121	163
Total	$ 9,662	$ 6,023	[1]
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Net Loss per Share - Computatio

Net Loss per Share - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net loss	$ (22,352)	$ (28,090)	$ (17,670)	$ (10,812)	$ (13,533)	$ (12,955)	$ (68,112)	$ (37,299)
Denominator:
Weighted-average common shares outstanding	45,787,137			44,452,184			45,253,176	33,937,800
Less: weighted-average common shares subject to vesting	(1,847,856)			(1,614,086)			(1,503,022)	(1,881,125)
Weighted-average number of shares used to compute basic and diluted net loss per share	43,939,281			42,838,098			43,750,154	32,056,675
Net loss per share: basic and diluted	$ (0.51)			$ (0.25)			$ (1.56)	$ (1.16)

Net Loss per Share - Summary of

Net Loss per Share - Summary of Outstanding Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss per Share (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	6,084,178	2,862,021
Common Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	4,274,163	1,348,955
Unvested Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	1,257,651	462,963
Unvested Early Exercised Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	552,364	1,050,103