Surface Oncology (SURF) 10-Q 12 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 07, 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	SURF
Entity Registrant Name	SURFACE ONCOLOGY, INC.
Entity Central Index Key	0001718108
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	true
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38459
Entity Tax Identification Number	46-5543980
Entity Address, Address Line One	50 Hampshire Street
Entity Address, Address Line Two	8th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	714-4096
Entity Common Stock, Shares Outstanding		27,882,756
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock, $0.0001
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 38,523	$ 82,912
Marketable securities	73,281	75,923
Prepaid expenses and other current assets	2,504	5,766
Total current assets	114,308	164,601
Property and equipment, net	7,628	8,226
Operating lease right-of-use asset	15,807
Restricted cash	1,198	1,198
Other assets	35	40
Total assets	138,976	174,065
Current liabilities:
Accounts payable	1,647	3,412
Accrued expenses and other current liabilities	8,433	8,803
Deferred revenue - related party	4,236	14,610
Deferred rent		352
Operating lease liability	1,257
Total current liabilities	15,573	27,177
Deferred revenue - related party, non-current	34,795	39,342
Deferred rent, non-current		4,684
Operating lease liability, non-current	19,623
Total liabilities	69,991	71,203
Commitments and contingencies (Note 12)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at September 30, 2019 and December 31, 2018; no shares issued and outstanding at September 30, 2019 and December 31, 2018
Common stock, $0.0001 par value; 150,000,000 shares authorized at September 30, 2019 and December 31, 2018, respectively; 27,882,756 and 27,772,600 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	3	3
Additional paid-in capital	174,485	169,784
Accumulated other comprehensive income (loss)	138	(119)
Accumulated deficit	(105,641)	(66,806)
Total stockholders’ equity	68,985	102,862
Total liabilities and stockholders’ equity	$ 138,976	$ 174,065

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, authorized	5,000,000	5,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized	150,000,000	150,000,000
Common stock, issued	27,882,756	27,772,600
Common stock, outstanding	27,882,756	27,772,600

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue - related party	$ 344	$ 1,730	$ 14,921	$ 49,653
Type of Revenue [Extensible List]	us-gaap:CollaborativeArrangementMember	us-gaap:CollaborativeArrangementMember	us-gaap:CollaborativeArrangementMember	us-gaap:CollaborativeArrangementMember
Operating expenses:
Research and development	$ 12,916	$ 15,783	$ 40,461	$ 41,971
General and administrative	4,984	3,977	15,494	11,252
Total operating expenses	17,900	19,760	55,955	53,223
Loss from operations	(17,556)	(18,030)	(41,034)	(3,570)
Interest and other income, net	678	808	2,199	1,708
Net loss	(16,878)	(17,222)	(38,835)	(1,862)
Accretion of redeemable convertible preferred stock to redemption value				(11)
Net loss attributable to common stockholders	$ (16,878)	$ (17,222)	$ (38,835)	$ (1,873)
Net loss per share attributable to common stockholders— basic and diluted	$ (0.61)	$ (0.62)	$ (1.39)	$ (0.11)
Weighted average common shares outstanding— basic and diluted	27,862,544	27,598,251	27,844,591	17,398,249
Comprehensive loss:
Net loss	$ (16,878)	$ (17,222)	$ (38,835)	$ (1,862)
Other comprehensive loss:
Unrealized gain (loss) on marketable securities, net of tax of $0	(36)	43	257	56
Comprehensive loss	$ (16,914)	$ (17,179)	$ (38,578)	$ (1,806)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)
Statement Of Income And Comprehensive Income [Abstract]
Marketable securities tax	$ 0

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders Equity (Deficit) - USD ($) $ in Thousands	Total	Series A and A-1 Redeemable Convertible Preferred Stock	Initial Public Offering	Private PlacementNovartis Institutes for Biomedical Research, Inc.	Common Stock	Common StockInitial Public Offering	Common StockPrivate PlacementNovartis Institutes for Biomedical Research, Inc.	Additional Paid-in Capital	Additional Paid-in CapitalInitial Public Offering	Additional Paid-in CapitalPrivate PlacementNovartis Institutes for Biomedical Research, Inc.	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2017	$ (67,314)							$ 6,877			$ (246)	$ (73,945)
Temporary equity beginning balance, share at Dec. 31, 2017		37,100,000
Temporary equity beginning balance at Dec. 31, 2017		$ 48,517
Beginning balance, share at Dec. 31, 2017					2,686,350
Issuance of common stock upon exercise of stock options	157							157
Issuance of common stock upon exercise of stock options, share					80,675
Stock-based compensation expense	1,291							1,291
Accretion of redeemable convertible preferred stockto redemption value		$ 11
Accretion of redeemable convertible preferred stock to redemption value	(11)							(11)
Adjustment due to the adoption of ASC 606	13,736											13,736
Unrealized gain (loss) on marketable securities	(50)										(50)
Net income (loss)	31,212											31,212
Ending balance at Mar. 31, 2018	(20,979)							8,314			(296)	(28,997)
Temporary equity ending balance, share at Mar. 31, 2018		37,100,000
Temporary equity ending balance at Mar. 31, 2018		$ 48,528
Ending balance, share at Mar. 31, 2018					2,767,025
Beginning balance at Dec. 31, 2017	(67,314)							6,877			(246)	(73,945)
Temporary equity beginning balance, share at Dec. 31, 2017		37,100,000
Temporary equity beginning balance at Dec. 31, 2017		$ 48,517
Beginning balance, share at Dec. 31, 2017					2,686,350
Unrealized gain (loss) on marketable securities	56
Net income (loss)	(1,862)
Ending balance at Sep. 30, 2018	106,020				$ 3			168,278			(190)	(62,071)
Ending balance, share at Sep. 30, 2018					27,607,213
Beginning balance at Mar. 31, 2018	(20,979)							8,314			(296)	(28,997)
Temporary equity beginning balance, share at Mar. 31, 2018		37,100,000
Temporary equity beginning balance at Mar. 31, 2018		$ 48,528
Beginning balance, share at Mar. 31, 2018					2,767,025
Issuance of common stock upon exercise of stock options	2							2
Issuance of common stock upon exercise of stock options, share					3,636
Stock-based compensation expense	1,490							1,490
Conversion of redeemable convertible preferred stock to common stock	48,528				$ 2			48,526
Temporary equity conversion of convertible preferred stock, shares		(37,100,000)
Temporary equity conversion of convertible preferred stock		$ (48,528)
Conversion of convertible preferred stock, shares					16,863,624
Issuance of common stock			$ 97,209	$ 11,500		$ 1			$ 97,208	$ 11,500
Issuance of common stock, shares						7,200,000	766,666
Unrealized gain (loss) on marketable securities	63										63
Net income (loss)	(15,852)											(15,852)
Ending balance at Jun. 30, 2018	121,961				$ 3			167,040			(233)	(44,849)
Ending balance, share at Jun. 30, 2018					27,600,951
Issuance of common stock upon exercise of stock options	24							24
Issuance of common stock upon exercise of stock options, share					23,197
Repurchases of unvested restricted stock, share					(16,935)
Stock-based compensation expense	1,214							1,214
Unrealized gain (loss) on marketable securities	43										43
Net income (loss)	(17,222)											(17,222)
Ending balance at Sep. 30, 2018	106,020				$ 3			168,278			(190)	(62,071)
Ending balance, share at Sep. 30, 2018					27,607,213
Beginning balance at Dec. 31, 2018	$ 102,862				$ 3			169,784			(119)	(66,806)
Beginning balance, share at Dec. 31, 2018	27,772,600				27,772,600
Issuance of common stock upon exercise of stock options	$ 211							211
Issuance of common stock upon exercise of stock options, share					58,082
Stock-based compensation expense	1,395							1,395
Unrealized gain (loss) on marketable securities	124										124
Net income (loss)	(4,199)											(4,199)
Ending balance at Mar. 31, 2019	100,393				$ 3			171,390			5	(71,005)
Ending balance, share at Mar. 31, 2019					27,830,682
Beginning balance at Dec. 31, 2018	$ 102,862				$ 3			169,784			(119)	(66,806)
Beginning balance, share at Dec. 31, 2018	27,772,600				27,772,600
Unrealized gain (loss) on marketable securities	$ 257
Net income (loss)	(38,835)
Ending balance at Sep. 30, 2019	$ 68,985				$ 3			174,485			138	(105,641)
Ending balance, share at Sep. 30, 2019	27,882,756				27,882,756
Beginning balance at Mar. 31, 2019	$ 100,393				$ 3			171,390			5	(71,005)
Beginning balance, share at Mar. 31, 2019					27,830,682
Issuance of common stock upon exercise of stock options	33							33
Issuance of common stock upon exercise of stock options, share					21,069
Stock-based compensation expense	1,485							1,485
Unrealized gain (loss) on marketable securities	169										169
Net income (loss)	(17,758)											(17,758)
Ending balance at Jun. 30, 2019	84,322				$ 3			172,908			174	(88,763)
Ending balance, share at Jun. 30, 2019					27,851,751
Issuance of common stock upon exercise of stock options	11							11
Issuance of common stock upon exercise of stock options, share					31,005
Stock-based compensation expense	1,566							1,566
Unrealized gain (loss) on marketable securities	(36)										(36)
Net income (loss)	(16,878)											(16,878)
Ending balance at Sep. 30, 2019	$ 68,985				$ 3			$ 174,485			$ 138	$ (105,641)
Ending balance, share at Sep. 30, 2019	27,882,756				27,882,756

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (38,835)	$ (1,862)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization expense	1,324	982
Stock-based compensation expense	4,446	3,995
Net amortization of premiums and discounts on marketable securities	(666)	(207)
Loss on disposal of property and equipment	1	13
Non-cash operating lease cost	865
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	3,262	3,398
Other assets	5	(54)
Accounts payable	(1,154)	1,144
Accrued expenses and other current liabilities	(301)	(1,964)
Deferred rent		(73)
Operating lease liability	(828)
Deferred revenue - related party	(14,921)	(4,652)
Net cash (used in) provided by operating activities	(46,802)	720
Cash flows from investing activities:
Purchases of property and equipment	(1,407)	(896)
Purchases of marketable investments	(107,784)	(107,258)
Proceeds from sales or maturities of marketable securities	111,349	16,592
Net cash provided by (used in) investing activities	2,158	(91,562)
Cash flows from financing activities:
Payments of offering costs		(2,031)
Proceeds from initial public offering of common stock, net of commissions and underwriting discounts		100,440
Proceeds from issuance of common stock to a related party		11,500
Proceeds from exercise of stock options	255	183
Net cash provided by financing activities	255	110,092
Net increase (decrease) in cash and cash equivalents and restricted cash	(44,389)	19,250
Cash and cash equivalents and restricted cash at beginning of period	84,110	23,540
Cash and cash equivalents and restricted cash at end of period	39,721	42,790
Supplemental disclosure of cash flow information:
Cash paid for income taxes		41
Supplemental disclosure of non-cash investing and financing activities:
Accretion of redeemable convertible preferred stock to redemption value		11
Purchases of property and equipment included in accounts payable and accrued expenses	$ 12	$ 322

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Surface Oncology, Inc. (the “Company” or “Surface”) is a clinical-stage immuno-oncology company focused on using its specialized knowledge of the biological pathways critical to the immunosuppressive tumor microenvironment (“TME”) for the development of next-generation cancer therapies. Surface was incorporated in April 2014 under the laws of the State of Delaware. The Company is subject to risks common to early-stage companies in the biotechnology industry including, but not limited to, development by competitors of new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the ability to obtain additional financing to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure, and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. On April 6, 2018, the Company effected a one-for-2.2 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s Redeemable Convertible Preferred Stock. Accordingly, all share and per share amounts for all periods presented in the accompanying condensed consolidated financial statements, and notes thereto, have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios. On April 23, 2018, the Company completed its initial public offering of its common stock by issuing 7,200,000 shares of common stock, at $15.00 per share for gross proceeds of $108,000, or net proceeds of $97,209 after deducting underwriting discounts, commissions and offering expenses. Concurrent with the initial public offering, the Company issued Novartis Institutes for Biomedical Research, Inc. (“Novartis”) 766,666 shares of its common stock at $15.00 per share for proceeds of $11,500, in a private placement. Upon the closing of the Company’s initial public offering on April 23, 2018, all shares of Series A and A-1 redeemable convertible preferred stock (the “Series A Preferred Stock” and “Series A-1 Preferred Stock”, respectively) automatically converted into 16,863,624 shares of common stock. On May 1, 2019, the Company entered into a Capital on Demand TM The Company’s financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. The Company has primarily funded its operations with proceeds from the sales of redeemable convertible preferred stock, proceeds from a collaboration agreement with Novartis, and proceeds from the Company’s initial public offering of common stock. The Company has incurred losses and negative cash flows from operations since its inception. As of September 30, 2019, the Company had an accumulated deficit of $105,641. The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. As of November 12, 2019, the issuance date of this Quarterly Report on Form 10-Q, the Company expects that its cash, cash equivalents and marketable securities of $111,804, will be sufficient to fund its operating expenses and capital expenditure requirements for at least the next 12 months. The future viability of the Company beyond that date is dependent on its ability to raise additional capital to finance its operations. The Company will seek additional funding through public financings, debt financings, collaboration agreements, strategic alliances, and licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborations or other arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be required to delay, reduce or eliminate research and development programs, product portfolio expansion, or future commercialization efforts, which could adversely affect its business prospects. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiary, Surface Securities Corporation, a Massachusetts corporation, after elimination of all intercompany accounts and transactions. The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 2 to the financial statements included in the Company’s Annual Report on Form 10-K, filed with the Securities and Exchange Commission (the “SEC”) on March 7, 2019, except for the Company’s adoption of the new leasing standard as discussed below. Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses, and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts, and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from the Company’s estimates. Leases The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use (“ROU”) assets, operating lease liability, and operating lease liability, non-current in the Company’s condensed consolidated balance sheets. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. Many lease agreements include the option to renew or extend the lease term. The exercise of lease renewal options or extensions is at the Company’s sole discretion, and are only included in the calculation of the operating lease ROU asset and operating lease liability when it is reasonably certain that the Company would exercise such options. As the Company’s leases do not provide an implicit rate, the Company uses its incremental borrowing rate, which it calculates based on the credit quality of the Company, and by comparing interest rates available in the market for similar borrowings, and adjusting this amount based on the impact of collateral over the term of each lease. The components of a lease are split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, maintenance, consumables, etc.), and non-components (e.g., property taxes, insurance, etc.). Then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain practical expedients are available to entities. Entities electing the practical expedient would not separate lease and non-lease components. Rather, they would account for each lease component and the related non-lease component together as a single component. The Company’s facilities operating leases have lease and non-lease components to which the Company has elected to apply the practical expedient and account for each lease component and related non-lease component as one single component. The Company also elected the package of practical expedients, which, among other things, allows the Company to carry forward prior conclusions related to whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases and initial direct costs for existing leases. The Company also made an accounting policy election not to recognize leases with an initial term of 12 months or less within its condensed consolidated balance sheets and to recognize those lease payments on a straight-line basis in its condensed consolidated statements of operations and comprehensive loss over the lease term. Unaudited Interim Financial Information The accompanying condensed consolidated balance sheet as of September 30, 2019, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2019 and 2018, the condensed consolidated statements of cash flows for the nine months ended September 30, 2019 and 2018, and the condensed consolidated statement of redeemable convertible preferred stock and stockholders’ equity (deficit) for the three and nine months ended September 30, 2019 and 2018 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2019 and the results of its operations and its cash flows for the nine months ended September 30, 2019 and 2018. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2019 and 2018 are also unaudited. The results for the three and nine months ended September 30, 2019 are not necessarily indicative of results to be expected for the year ending December 31, 2019, any other interim periods, or any future year period. Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (ASU) No. 2016-02, Leases “Codification Improvements to Topic 842, Leases” The Company adopted ASC 842 using the modified retrospective approach with an effective date of January 1, 2019 for leases that existed on that date. Prior period results continue to be presented under ASC 840 based on the accounting standards originally in effect for such periods. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which, among other things, allows the Company to carry forward the historical lease classification. In connection with the adoption of ASC 842, the Company recorded an impact of $16,672 on its assets and $21,708 on its liabilities for the recognition of operating lease right-of-use-assets and operating lease liabilities, respectively, which are primarily related to the lease of the Company’s corporate headquarters in Cambridge, Massachusetts. The adoption of ASC 842 did not have a material impact on the Company’s results of operations or cash flows. In July 2017, the FASB issued ASU 2017-11, Earnings Per Share, Distinguishing Liabilities from Equity, Derivatives and Hedging (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception The Company adopted . The adoption of this guidance did not have a material impact on the Company's financial position or its results of operations. In June 2018, the FASB issued ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). The new standard simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The Company adopted ASU 2018-07 . As a result of adopting this standard, the fair value of outstanding nonemployee awards as of December 31, 2018 will no longer be remeasured each reporting period. All future expense related to these awards will be recorded based on the fair value measured as of January 1, 2019. The adoption of this guidance did not have a material impact of the Company’s consolidated financial statements. Recently Issued Accounting Pronouncements In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, (“ASU 2018-13”). Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s financial statements upon adoption.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2019
Marketable Securities [Abstract]
Marketable Securities	3. Marketable Securities As of September 30, 2019, the fair value of available-for-sale marketable debt securities by type of security was as follows: September 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable debt securities: U.S. Treasury notes $ 57,211 $ 92 $ (2 ) $ 57,301 U.S. Government agency bonds 15,932 48 — 15,980 $ 73,143 $ 140 $ (2 ) $ 73,281 The amortized cost and fair value of the Company’s available-for-sale debt securities by contractual maturity are summarized as follows: September 30, 2019 Amortized Cost Fair Value Maturing in one year or less $ 73,143 $ 73,281 $ 73,143 $ 73,281 As of December 31, 2018, the fair value of available-for-sale marketable debt securities by type of security was as follows: December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable debt securities: U.S. Treasury notes $ 62,866 $ — $ (24 ) $ 62,842 U.S. Government agency bonds 2,900 — (15 ) 2,885 Corporate bonds 10,276 — (80 ) 10,196 $ 76,042 $ — $ (119 ) $ 75,923 The amortized cost and fair value of the Company’s available-for-sale securities by contractual maturity are summarized as follows: December 31, 2018 Amortized Cost Fair Value Maturing in one year or less $ 76,042 $ 75,923 $ 76,042 $ 75,923 The Company determined that there was no material change in the credit risk of these investments. As a result, the Company determined it did not hold any investments with an other-than-temporary decline in fair value as of September 30, 2019 and December 31, 2018.

Fair Value of Financial Assets

Fair Value of Financial Assets	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets	4. Fair Value of Financial Assets The following tables present information about the Company’s financial assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of September 30, 2019 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 27,739 $ — $ — $ 27,739 Marketable securities: U.S. Treasury notes — 57,301 — 57,301 U.S. Government agency bonds — 15,980 — 15,980 $ 27,739 $ 73,281 $ — $ 101,020 Fair Value Measurements as of December 31, 2018 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 77,737 $ — $ — $ 77,737 Marketable securities: U.S. Treasury notes — 62,842 — $ 62,842 U.S. Government agency bonds — 2,885 — 2,885 Corporate bonds — 10,196 — 10,196 $ 77,737 $ 75,923 $ — $ 153,660 As of September 30, 2019 and December 31, 2018, the Company’s cash equivalents were invested in money market funds and were valued based on Level 1 inputs. During the nine months ended September 30, 2019 and 2018, there were no transfers between Level 1, Level 2 and Level 3.

Collaboration Agreement with No

Collaboration Agreement with Novartis	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Agreement with Novartis	5. Collaboration Agreement with Novartis Overview In January 2016, the Company entered into a collaboration agreement with Novartis (the “Collaboration Agreement”), which was subsequently amended in May 2016, July 2017, September 2017, and October 2018 (the “October 2018 Amendment”). Pursuant to the Collaboration Agreement, the Company granted Novartis a worldwide exclusive license to research, develop, manufacture and commercialize antibodies that target cluster of differentiation, or CD, 73 (“CD73”). In addition, the Company granted Novartis the right to purchase exclusive option rights (each an “Option”) for up to four specified targets (each an “Option Target”) including certain development, manufacturing, and commercialization rights. Novartis initially had the right to exercise up to three purchased Options. Under the Collaboration Agreement, therefore, Novartis had the ability to exclusively license the development and manufacturing rights for up to four targets (inclusive of CD73). Of these, the Company had the right to retain commercialization rights in the United States to two of such targets. As of September 30, 2019, Novartis has one Option remaining eligible for purchase, and potential exercise. The Collaboration Agreement is governed by a joint steering committee that is co-chaired by a chairperson designated by each of the Company and Novartis. The October 2018 Amendment, among other things, modified certain definitions and provisions of the Collaboration Agreement to make them consistent with the amended and restated development and option agreement the Company entered into with Adimab LLC in October and clarified the parties’ rights and responsibilities relating to the amended agreement with Adimab LLC and diagnostic products. Novartis is a related party because it is a greater than 5% stockholder of the Company. In January 2016, the Company entered into the Collaboration Agreement and sold 2,000,000 shares of its Series A-1 preferred stock to Novartis. In addition, concurrent with the Company’s initial public offering of common stock, the Company issued Novartis 766,666 shares of its common stock at $15.00 per share for proceeds of $11,500 in a private placement. During the nine months ended September 30, 2019, the Company made no cash payments to Novartis related to the Collaboration Agreement. During the nine months ended September 30, 2018, th e Company made a payment of $3,543 to Novartis for the reimbursement of manufacturing costs incurred by Novartis prior to December 31, 2017. Research on Targets Under the Collaboration Agreement, the Company is responsible for performing preclinical research through the first investigational new drug application (“IND”) acceptance on antibodies that bind to CD73 and each Option Target, pursuant to a research plan directed toward each target. The Company is responsible for all costs and expenses incurred by or on its behalf, in connection with such research. Development and Commercialization of CD73 Products Novartis has the sole right to develop and commercialize CD73 antibody candidates and corresponding licensed products worldwide pursuant to a development plan and a commercialization plan, respectively. Novartis is obligated to use commercially reasonable efforts to develop the CD73 antibody candidates and corresponding licensed products, to obtain regulatory approval of such products, including within certain defined markets, and to commercialize such products following regulatory approval. Novartis is responsible for all costs and expenses of such development and commercialization and is obligated to provide the Company with updates on its development and commercialization activities through the joint steering committee, joint development committee, and joint commercialization committee. Option Targets Prior to the filing of an IND for an Option Target, Novartis may purchase the Option to obtain certain development, manufacturing and commercialization rights for antibodies that bind to the Option Target. To the extent Novartis does not elect to purchase an Option to an Option Target, the Option for such Option Target will expire and all rights to such Option Target under the Collaboration Agreement will terminate. Novartis had the right to exercise up to a total of three purchased Options. Each exercised Option is to be designated as either a regional or global option, with each such designation determining the development, manufacturing, and commercialization rights between the parties with respect to such Option Target, corresponding antibody candidates, and licensed products, as summarized below. Novartis has the ability to designate the remaining Option as either regional or global. Following Novartis’ exercise of an Option with respect to an Option Target, the Company will grant to Novartis licenses that are necessary to effectuate the development, manufacturing or commercialization rights associated with a regional or global option, as described below. In December 2016, Novartis purchased the Option for antibodies that bind to CD47 for $5,000. In March 2018, Novartis notified the Company of its decision not to exercise its purchased Option related to CD47. In March 2018, the Company and Novartis also mutually agreed to cease development of one of the undisclosed programs subject to the Collaboration Agreement. In February 2019, Novartis notified the Company of its decision not to purchase the Option related to IL-27. Development and Commercialization of Regional Licensed Products To the extent an exercised Option is designated as regional, the Company is primarily responsible for the early clinical development of each corresponding regional antibody candidate and regional licensed product at its own cost. Unless the Company chooses to opt out of its development rights, it will collaborate with Novartis on the further clinical development of regional antibody candidates and regional licensed products. Pursuant to a regional development plan for each regional licensed product, the Company will be responsible for development activities related to obtaining regulatory approval in the United States, with Novartis responsible for development activities related to obtaining regulatory approval elsewhere in the world. The development costs of such later clinical development activities will be split evenly among the parties. Thereafter, the Company is responsible for the commercialization of regional licensed products in the United States, and Novartis is responsible for the commercialization of regional licensed products outside of the United States, each pursuant to a commercialization plan. Each party must use commercially reasonable efforts to commercialize such products within their respective territories. The Company is obligated to work with Novartis to agree to a global commercialization strategy with respect to the regional licensed products prior to commercialization. Development and Commercialization of Global Licensed Products To the extent an exercised Option is designated as global, the Company is primarily responsible for the early clinical development of each global antibody candidate and global licensed product at the Company’s own cost, and Novartis is solely responsible for the later worldwide clinical development of global antibody candidates and global licensed products, pursuant to a development plan for such global licensed product, at its own cost. Novartis is solely responsible for the worldwide commercialization of global licensed products and must use commercially reasonable efforts to commercialize such products, pursuant to a commercialization plan, at its own cost. Novartis agrees to provide the Company with development and commercialization updates regarding global licensed products through the joint steering committee, joint development committee, and joint commercialization committee. Exclusivity Neither the Company nor Novartis may, alone or with any affiliate or third party, (i) research or develop any antibody that specifically binds to an Option Target for a specified period of time outside of the Collaboration Agreement or (ii) develop or commercialize any antibody that specifically binds to CD73 or any Option Target that subsequently becomes a licensed target for a specified period of time outside the Collaboration Agreement. The October 2018 Amendment clarified that Novartis is permitted to research, develop, manufacture or commercialize any diagnostic product that specifically binds to a licensed target, subject to Novartis’ compliance with its rights and obligations under the Collaboration Agreement, and provided that where such diagnostic product is an Adimab diagnostic product, Novartis may research, develop, manufacture or commercialize such Adimab diagnostic product solely for the purpose of research, development or commercialization of a therapeutic or prophylactic licensed product that specifically binds to the same licensed target. Financial Terms Upon entering into the Collaboration Agreement in January 2016, Novartis made an upfront payment to the Company of $70,000. In addition, Novartis is obligated to pay the Company a fee to the extent it desires to purchase an Option for any Option Target and another fee to exercise such purchased Option, which entitles the Company to an aggregate of up to $20,000 in option purchase and option exercise payments for the remaining Option. The Company is also eligible to receive payments on a target-by-target basis upon the achievement of specified development and sales milestones as well as tiered royalties on annual net sales by Novartis of licensed products ranging from high single-digit to mid-teens percentages upon successful commercialization of any products. Under the Collaboration Agreement, the Company is currently entitled to potential milestones in excess of $500,000, as well as tiered royalties on annual net sales by Novartis ranging from high single-digit to mid-teens percentages upon the successful commercialization of NZV930 (formally SRF373). The maximum aggregate amount of potential option purchase, option exercise, and milestone payments associated with Novartis’ single remaining Option is $220,000, as well as tiered royalties on annual net sales by Novartis ranging from high-single-digit to low double-digit percentages upon the successful commercialization of the remaining Option Target. The Company is required to pay Novartis tiered royalties ranging from high single-digit to mid-teens percentages on annual net sales by the Company of regional licensed products in the United States. The royalty payments are subject to reduction under specified conditions set forth in the Collaboration Agreement. Termination Unless terminated earlier, the Collaboration Agreement will continue in effect until neither the Company nor Novartis is researching, developing, manufacturing, or commercializing any antibody candidates or licensed products under the Collaboration Agreement. Novartis may terminate the Collaboration Agreement on a target-by-target basis for any reason upon prior notice to the Company within a specified time period. Either party may terminate the Collaboration Agreement in full, or on a target-by-target basis, if an undisputed material breach is not cured within a certain period of time or upon notice of insolvency of the other party. To the extent Novartis terminates for convenience, or the Company terminates for Novartis’ material breach, Novartis will grant the Company, on mutually agreeable financial terms, an exclusive, worldwide, irrevocable, perpetual and royalty-bearing license with respect to intellectual property controlled by Novartis that is reasonably necessary to research, develop, manufacture or commercialize certain products. Revenue Recognition – Collaboration Revenue – Related Party In determining the appropriate amount of revenue to be recognized under ASC 606, the Company performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Under ASC 606, the Company recognized revenue using the cost-to-cost method, which it believes best depicts the transfer of control to the customer. Under the cost-to-cost method, the extent of progress towards completion is measured based on the ratio of actual costs incurred to the total estimated costs expected upon satisfying the identified performance obligation. Under this method, revenue will be recorded as a percentage of the estimated transaction price based on the extent of progress towards completion. Under ASC 606, the estimated transaction price will include variable consideration. The Company does not include variable consideration to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will occur when any uncertainty associated with the variable consideration is resolved. The estimate of the Company’s measure of progress and estimate of variable consideration to be included in the transaction price will be updated at each reporting date as a change in estimate. The amount related to the unsatisfied portion will be recognized as that portion is satisfied over time. Under ASC 606 the Company accounts for (i) the license it conveyed with respect to CD73; and (ii) its obligations to perform research on CD73 and other specified targets as a single performance obligation under the collaboration agreement with Novartis. Novartis’ right to purchase exclusive options to obtain certain development, manufacturing and commercialization rights are accounted for separately as they do not represent material rights, based on the criteria of ASC 606. Upon the exercise of any purchased option by Novartis, the contract promises associated with an option target would use a separate cost-to-cost model for purposes of revenue recognition under ASC 606. In February 2018, the Company received an additional milestone payment of $45,000 from Novartis upon Novartis’ receipt and acceptance of the first final audited Good Laboratory Practices (“GLP”) toxicology study report for NZV930. Upon achieving the milestone, the Company concluded this variable consideration associated with this milestone was no longer constrained and included the $45,000 in the transaction price. In March 2018, Novartis notified the Company of its decision not to exercise its Option related to CD47. The Company recognized the $5,000 exclusive option right payment as collaboration revenue – related party in the first quarter of 2018 because the Company no longer has any remaining performance obligations related to CD47. In March 2018, the Company and Novartis elected to terminate a specified target under the Collaboration Agreement. Future costs associated with this target were removed from the estimated total costs in the cost-to-cost model. In February 2019, Novartis notified the Company of its decision not to purchase the Option related to IL-27. Future costs associated with this target were removed from the estimated total costs in the cost-to-cost model. For the three and nine months ended September 30, 2019 and 2018, the Company recognized the following totals of collaboration revenue – related party: Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Collaboration revenue - related party $ 344 $ 1,730 $ 14,921 $ 49,653 The following table presents changes in the Company’s contract liabilities during the nine months ended September 30, 2019: December 31, 2018 Additions Deductions September 30, 2019 Contract liabilities (1) Total deferred revenue - related party $ 53,952 $ — $ (14,921 ) $ 39,031 (1) Additions to contract liabilities relate to consideration from Novartis during the reporting period. Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period. During $344 and of revenue, respectively, related to the amounts included in contract liability balance at the beginning of the period. The aggregate amount of the transaction price allocated to the single performance obligation that is partially unsatisfied was The Company

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2019
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock	6. Redeemable Convertible Preferred Stock The Company has issued Series A and Series A-1 preferred stock (together, the “Redeemable Convertible Preferred Stock”). The Redeemable Convertible Preferred Stock is classified outside of stockholders’ deficit because the shares contain redemption features that are not solely within the control of the Company. Upon the closing of the Company’s initial public offering on April 23, 2018, all shares of the Redeemable Convertible Preferred Stock automatically converted into 16,863,624 shares of common stock.

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Stockholders' Equity (Deficit)	7. Stockholders’ Equity (Deficit) Common Stock As of September 30, 2019 and December 31, 2018, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 150,000,000 shares, of $0.0001 par value common stock. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the board of directors, if any, subject to the preferential dividend rights of any outstanding preferred stock. No dividends have been declared or paid by the Company through September 30, 2019. As of September 30, 2019 and December 31, 2018, the Company had reserved 17,361,676 and 6,083,202 shares, respectively, of common stock for the exercise of outstanding stock options, shares to be issued under the ATM Facility, and the number of shares remaining available for future grant under the Company’s 2018 Stock Option and Incentive Plan, and 2018 Employee Stock Purchase Plan. In May 2019, the Company entered into the Sales Agreement with JonesTrading to issue and sell shares up to $30,000 in shares of the Company’s common stock from time to time. The Company has not yet issued or sold any securities under the Sales Agreement. On April 23, 2018, the Company completed its initial public offering of its common stock by issuing 7,200,000 shares of common stock, at $15.00 per share for gross proceeds of $108,000, or net proceeds of $97,209. Concurrent with the initial public offering, the Company issued Novartis 766,666 shares of its common stock at $15.00 per share for proceeds of $11,500, in a private placement

Stock-Based Awards

Stock-Based Awards	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	8. Stock-Based Awards 2014 Stock Incentive Plan The Company’s 2014 Stock Incentive Plan (the “2014 Plan”) provides for the Company to grant incentive stock options or nonqualified stock options, restricted stock awards, unrestricted stock awards or restricted stock units to employees, directors and consultants of the Company. The 2014 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of the stock options may not be less than 100% of the fair market value of a share of the Company’s common stock on the date of grant and the term of the stock options may not be greater than ten years. As of September 30, 2019 and December 31, 2018, all remaining shares available under the 2014 Plan were transferred to the Company’s 2018 Stock Option and Incentive Plan (the “2018 Plan”). 2018 Stock Option and Incentive Plan On April 3, 2018, the Company’s stockholders approved the 2018 Plan, which became effective on April 18, 2018, the date on which the registration statement for the Company’s initial public offering was declared effective. The 2018 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights to the Company’s officers, employees, non-employee directors and other key persons (including consultants). The number of shares initially reserved for issuance under the 2018 Plan was 1,545,454, plus the shares of common stock remaining available for issuance under the 2014 Plan, which shall be cumulatively increased each January 1 by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s board of directors or compensation committee of the board of directors. The shares of common stock underlying any awards that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire or are otherwise terminated (other than by exercise) under the 2018 Plan and the 2014 Plan will be added back to the shares of common stock available for issuance under the 2018 Plan. As of September 30, 2019, 1,314,753 shares were available for future issuance under the 2018 Plan. Stock options granted under the 2014 Plan and 2018 Plan to employees generally vest over four years and expire after ten years. Stock Options The following table summarizes the Company’s stock option activity since January 1, 2019: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding as of December 31, 2018 4,414,225 $ 6.79 8.29 $ 2,031 Granted 1,411,597 4.27 Exercised (110,156 ) 2.31 Forfeited (203,287 ) 6.94 Outstanding as of September 30, 2019 5,512,379 $ 6.22 8.05 $ 437 Options exercisable at September 30, 2019 2,591,780 $ 5.49 7.37 $ 427 Vested and expected to vest at September 30, 2019 5,512,379 $ 6.22 8.05 $ 437 The weighted average grant-date fair value per share of stock options granted during the nine months ended September 30, 2019 and year ended December 31, 2018 was $2.85 and $7.47, respectively. As of September 30, 2019 and December 31, 2018, there were outstanding stock options held by non-employees for the purchase of 278,735 and 317,957 shares of common stock, respectively, with service-based vesting conditions. 2018 Employee Stock Purchase Plan On April 3, 2018, the Company’s stockholders approved the 2018 Employee Stock Purchase Plan (the “ESPP”), which became effective on April 18, 2018, the date on which the registration statement for the Company’s initial public offering was declared effective. A total of 256,818 shares of common stock were initially reserved for issuance under this plan. In addition, the number of shares of common stock that may be issued under the ESPP automatically increased on January 1, 2019, and shall increase each January 1 thereafter through January 1, 2028, by the lesser of (i) 1% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 and (ii) such lesser number of shares as determined by the administrator of the Company’s ESPP. As of September 30, 2019, a total of 534,544 shares of common stock were reserved for issuance under this plan. For the nine months ended September 30, 2019 and 2018, the Company did not issue any shares of common stock under the 2018 ESPP. Stock-Based Compensation The Company recorded stock-based compensation expense related to stock options and restricted stock awards in the following expense categories of its statements of operations and comprehensive loss: Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Research and development expenses $ 596 $ 470 $ 1,767 $ 2,111 General and administrative expenses 970 744 2,679 1,884 $ 1,566 $ 1,214 $ 4,446 $ 3,995 As of September 30, 2019, the Company had an aggregate of $12,890 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.04 years.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Loss per Share	9. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Basic and diluted net loss per share attributable to common stockholders: Numerator: Net loss $ (16,878 ) $ (17,222 ) $ (38,835 ) $ (1,862 ) Accretion of redeemable convertible preferred stock to redemption value — — — (11 ) Net loss attributable to common stockholders $ (16,878 ) $ (17,222 ) $ (38,835 ) $ (1,873 ) Denominator: Weighted average commons shares outstanding — basic and diluted 27,862,544 27,598,251 27,844,591 17,398,249 Net loss per share attributable to common stockholders — basic and diluted $ (0.61 ) $ (0.62 ) $ (1.39 ) $ (0.11 ) The Company’s potential dilutive securities have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated above because including them would have had an anti-dilutive effect: September 30, 2019 2018 Stock options to purchase common stock 5,512,379 4,509,041 Shares to be issued under the 2018 ESPP 78,714 — 5,591,093 4,509,041

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes The Company did not provide for any income taxes for the three and nine months ended September 30, 2019 or 2018. The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of September 30, 2019 and December 31, 2018. Management reevaluates the positive and negative evidence at each reporting period. As of September 30, 2019 and December 31, 2018, the Company had no accrued interest or tax penalties recorded. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. The Company is currently under examination by the Internal Revenue Service ("IRS") for the period ended December 31, 2016. The Company's tax years are still open under statute from 2015 to present. All years may be examined to the extent the tax credit or net operating loss carryforwards are used in future periods.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	11. Leases The Company leases real estate, primarily its corporate headquarters in Cambridge, Massachusetts. The Company’s leases have remaining terms ranging from less than 1 year to 10 years. Certain leases include options to renew, exercised at the Company’s sole discretion, with renewal terms that can extend the lease five years. The Company evaluated the renewal options in its leases to determine if it was reasonably certain that the renewal option would be exercised, and therefore should be included in the calculation of the operating lease assets and operating lease liabilities. Given the Company’s current business structure, uncertainty of future growth, and the associated impact to real estate, the Company concluded that it is not reasonably certain that the renewal option related to its corporate headquarters would be exercised, however, for leases it determined the renewal option was probable to be exercised, the Company included the renewal period in the calculation of the operating lease right-of-use With the adoption of the new leasing standard, the Company has recorded a right-of-use asset and corresponding lease liability, by calculating the present value of future lease payments, discounted at either 9.5% or 10.5%, the Company’s incremental borrowing rates, over the expected term. The right-of-use asset is reduced by any lease incentives received and the legacy deferred rent balance. The components of the Company’s lease expense are as follows: Lease Costs Classification Three months ended September 30, 2019 Nine months ended September 30, 2019 Operating lease cost R&D Expense 575 1,733 G&A Expense 234 695 Variable lease costs (1) R&D Expense 191 532 G&A Expense 78 214 Total lease cost 1,078 3,174 Weighted-average remaining lease term (in months) 120.0 Weighted-average discount rate 10.5 % (1) Variable lease costs include certain additional charges for operating costs, including insurance, maintenance, taxes, utilities, and other costs incurred, which are billed based on both usage and as a percentage of the Company’s share of total square footage. Short term lease costs are immaterial. Cash paid for amounts included in the measurement of the Company’s operating lease liabilities was $1,068 and $3,137 for the three and nine months ended September 30, 2019, respectively. As of September 30, 2019, the maturities of the Company’s operating lease liabilities were as follows: Year Ending December 31, 2019 800 2020 4,922 2021 5,861 2022 5,468 2023 5,410 Thereafter 37,573 Total future lease payments 60,034 Less: Interest (39,154 ) Present value of future lease payments (lease liability) $ 20,880 Future minimum lease payments for the Company’s operating leases as of December 31, 2018 were as follows: Year Ending December 31, 2019 2,546 2020 4,258 2021 5,176 2022 5,292 2023 5,376 Thereafter 37,573 $ 60,221 Prior to the adoption of ASU 2016-02 and for the three and nine months ended September 30, 2018, the Company recognized rent expense on a straight-line basis over the lease period and recorded deferred rent expense for rent expense incurred but not yet paid. The Company also recorded deferred rent attributable to cash incentives received under its lease agreements which were amortized to rent expense over the lease term. During the three and nine months ended September 30, 2018, the Company recognized total rent expense of $711 and $2,048, respectively. Sublease payments received from a third-party tenant under a sublease that expired in March 2018 were $3 and $231 for the three and nine months ended September 30, 2018, respectively, and were recorded as reduction of rent expense.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies Legal Proceedings On September 13, 2019, a purported stockholder of the Company filed a putative class action against the Company, certain of the Company’s directors and officers, or the Individual Defendants, and the underwriters in the Company’s initial public offering, collectively, the Defendants, in the Supreme Court of the State of New York, captioned Ang v. Surface Oncology, Inc., et al., No. 655304/2019 (N.Y. Sup. Ct. Sept. 13, 2019). The complaint was filed on behalf of a putative class of purchasers of the Company’s common stock in and/or traceable to the Company’s April 19, 2018 initial public offering (the first day of trading of our common stock on the Nasdaq Stock Market) and alleges violations of Section 11 (against all Defendants) and 15 (against the Company and the Individual Defendants) of the Securities Act of 1933, as amended. The complaint alleges that the Defendants made false or misleading statements in the Company’s Registration Statement on Form S-1 for the Company’s initial public offering regarding SRF231 and hematologic toxicities allegedly caused by SRF231. The lawsuit seeks, among other things, compensatory damages and interest thereon, and reasonable costs and expenses, including attorneys’ fees. While the Company is defending against all claims asserted, this litigation could result in substantial costs to the Company and a diversion of the Company’s management’s attention and resources, which could harm its business. In addition, the uncertainty of the pending lawsuit or potential filing of additional lawsuits could lead to more volatility and a reduction in the Company’s stock price. Given the early stage of the litigation, at this time the Company is unable to reasonably estimate possible losses or form a judgment that an unfavorable outcome is either probable or remote. It is not currently possible to assess whether or not the outcome of these proceedings may have a material adverse effect on the Company.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2019
Related Party Transactions [Abstract]
Related Party Transactions	13. Related Party Transactions Novartis Institutes for BioMedical Research, Inc. Novartis is a related party because it is a greater than 5% stockholder of the Company. In January 2016, the Company entered into the Collaboration Agreement and sold 2,000,000 shares of its Series A-1 preferred stock to Novartis for gross proceeds of $13,500. In addition, concurrent with the Company’s initial public offering of common stock, the Company issued Novartis 766,666 shares of its common stock at $15.00 per share, for proceeds of $11,500 in a private placement. During the three and nine months ended September 30, 2019, the Company recognized $344 and $14,921 of collaboration revenue under the Collaboration Agreement, respectively. As of September 30, 2019 and 2018, no amounts were due from Novartis. During the nine months ended September 30, 2019, the Company made no cash payments to Novartis related to the Collaboration Agreement. During the nine months ended September 30, 2018, the Company made a payment of $3,543 to Novartis for the reimbursement of manufacturing costs incurred by Novartis prior to December 31, 2017, as well as rent and utilities. Research Agreement with Vaccinex, Inc. On November 30, 2017, the Company entered into an agreement with Vaccinex, Inc. (“Vaccinex”) whereby Vaccinex will use its technology to assist the Company with identifying and selecting experimental human monoclonal antibodies against targets selected by the Company. The Company’s Chief Executive Officer is a member of the board of directors of Vaccinex. During the three and nine months ended September 30, 2019, the Company paid Vaccinex an aggregate of $425 and $602, respectively, relating to the agreement. During the three and nine months ended September 30, 2018, the Company paid Vaccinex an aggregate of $64 and $133, respectively, relating to the agreement. The payments were recognized as research and development expense. There was no amount due by the Company to Vaccinex as of September 30, 2019. The amount due by the Company to Vaccinex as of September 30, 2018 was $66.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiary, Surface Securities Corporation, a Massachusetts corporation, after elimination of all intercompany accounts and transactions. The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 2 to the financial statements included in the Company’s Annual Report on Form 10-K, filed with the Securities and Exchange Commission (the “SEC”) on March 7, 2019, except for the Company’s adoption of the new leasing standard as discussed below.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses, and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts, and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from the Company’s estimates.
Leases	Leases The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use (“ROU”) assets, operating lease liability, and operating lease liability, non-current in the Company’s condensed consolidated balance sheets. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. Many lease agreements include the option to renew or extend the lease term. The exercise of lease renewal options or extensions is at the Company’s sole discretion, and are only included in the calculation of the operating lease ROU asset and operating lease liability when it is reasonably certain that the Company would exercise such options. As the Company’s leases do not provide an implicit rate, the Company uses its incremental borrowing rate, which it calculates based on the credit quality of the Company, and by comparing interest rates available in the market for similar borrowings, and adjusting this amount based on the impact of collateral over the term of each lease. The components of a lease are split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, maintenance, consumables, etc.), and non-components (e.g., property taxes, insurance, etc.). Then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain practical expedients are available to entities. Entities electing the practical expedient would not separate lease and non-lease components. Rather, they would account for each lease component and the related non-lease component together as a single component. The Company’s facilities operating leases have lease and non-lease components to which the Company has elected to apply the practical expedient and account for each lease component and related non-lease component as one single component. The Company also elected the package of practical expedients, which, among other things, allows the Company to carry forward prior conclusions related to whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases and initial direct costs for existing leases. The Company also made an accounting policy election not to recognize leases with an initial term of 12 months or less within its condensed consolidated balance sheets and to recognize those lease payments on a straight-line basis in its condensed consolidated statements of operations and comprehensive loss over the lease term.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying condensed consolidated balance sheet as of September 30, 2019, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2019 and 2018, the condensed consolidated statements of cash flows for the nine months ended September 30, 2019 and 2018, and the condensed consolidated statement of redeemable convertible preferred stock and stockholders’ equity (deficit) for the three and nine months ended September 30, 2019 and 2018 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2019 and the results of its operations and its cash flows for the nine months ended September 30, 2019 and 2018. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2019 and 2018 are also unaudited. The results for the three and nine months ended September 30, 2019 are not necessarily indicative of results to be expected for the year ending December 31, 2019, any other interim periods, or any future year period.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (ASU) No. 2016-02, Leases “Codification Improvements to Topic 842, Leases” The Company adopted ASC 842 using the modified retrospective approach with an effective date of January 1, 2019 for leases that existed on that date. Prior period results continue to be presented under ASC 840 based on the accounting standards originally in effect for such periods. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which, among other things, allows the Company to carry forward the historical lease classification. In connection with the adoption of ASC 842, the Company recorded an impact of $16,672 on its assets and $21,708 on its liabilities for the recognition of operating lease right-of-use-assets and operating lease liabilities, respectively, which are primarily related to the lease of the Company’s corporate headquarters in Cambridge, Massachusetts. The adoption of ASC 842 did not have a material impact on the Company’s results of operations or cash flows. In July 2017, the FASB issued ASU 2017-11, Earnings Per Share, Distinguishing Liabilities from Equity, Derivatives and Hedging (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception The Company adopted . The adoption of this guidance did not have a material impact on the Company's financial position or its results of operations. In June 2018, the FASB issued ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). The new standard simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The Company adopted ASU 2018-07 . As a result of adopting this standard, the fair value of outstanding nonemployee awards as of December 31, 2018 will no longer be remeasured each reporting period. All future expense related to these awards will be recorded based on the fair value measured as of January 1, 2019. The adoption of this guidance did not have a material impact of the Company’s consolidated financial statements.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, (“ASU 2018-13”). Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s financial statements upon adoption.

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Marketable Securities [Abstract]
Summary of Fair Value of Available-for-sale Marketable Debt Securities by Type of Security	As of September 30, 2019, the fair value of available-for-sale marketable debt securities by type of security was as follows: September 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable debt securities: U.S. Treasury notes $ 57,211 $ 92 $ (2 ) $ 57,301 U.S. Government agency bonds 15,932 48 — 15,980 $ 73,143 $ 140 $ (2 ) $ 73,281 As of December 31, 2018, the fair value of available-for-sale marketable debt securities by type of security was as follows: December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable debt securities: U.S. Treasury notes $ 62,866 $ — $ (24 ) $ 62,842 U.S. Government agency bonds 2,900 — (15 ) 2,885 Corporate bonds 10,276 — (80 ) 10,196 $ 76,042 $ — $ (119 ) $ 75,923
Summary of Available-for-sale Debt Securities by Contractual Maturity	The amortized cost and fair value of the Company’s available-for-sale debt securities by contractual maturity are summarized as follows: September 30, 2019 Amortized Cost Fair Value Maturing in one year or less $ 73,143 $ 73,281 $ 73,143 $ 73,281 The amortized cost and fair value of the Company’s available-for-sale securities by contractual maturity are summarized as follows: December 31, 2018 Amortized Cost Fair Value Maturing in one year or less $ 76,042 $ 75,923 $ 76,042 $ 75,923

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s financial assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of September 30, 2019 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 27,739 $ — $ — $ 27,739 Marketable securities: U.S. Treasury notes — 57,301 — 57,301 U.S. Government agency bonds — 15,980 — 15,980 $ 27,739 $ 73,281 $ — $ 101,020 Fair Value Measurements as of December 31, 2018 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 77,737 $ — $ — $ 77,737 Marketable securities: U.S. Treasury notes — 62,842 — $ 62,842 U.S. Government agency bonds — 2,885 — 2,885 Corporate bonds — 10,196 — 10,196 $ 77,737 $ 75,923 $ — $ 153,660

Collaboration Agreement with _2

Collaboration Agreement with Novartis (Tables)	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Collaboration Revenue Related Party	For the three and nine months ended September 30, 2019 and 2018, the Company recognized the following totals of collaboration revenue – related party: Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Collaboration revenue - related party $ 344 $ 1,730 $ 14,921 $ 49,653
Summary of Changes in Contract Liabilities	The following table presents changes in the Company’s contract liabilities during the nine months ended September 30, 2019: December 31, 2018 Additions Deductions September 30, 2019 Contract liabilities (1) Total deferred revenue - related party $ 53,952 $ — $ (14,921 ) $ 39,031 (1) Additions to contract liabilities relate to consideration from Novartis during the reporting period. Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period.

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity since January 1, 2019: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding as of December 31, 2018 4,414,225 $ 6.79 8.29 $ 2,031 Granted 1,411,597 4.27 Exercised (110,156 ) 2.31 Forfeited (203,287 ) 6.94 Outstanding as of September 30, 2019 5,512,379 $ 6.22 8.05 $ 437 Options exercisable at September 30, 2019 2,591,780 $ 5.49 7.37 $ 427 Vested and expected to vest at September 30, 2019 5,512,379 $ 6.22 8.05 $ 437
Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Stock Awards	The Company recorded stock-based compensation expense related to stock options and restricted stock awards in the following expense categories of its statements of operations and comprehensive loss: Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Research and development expenses $ 596 $ 470 $ 1,767 $ 2,111 General and administrative expenses 970 744 2,679 1,884 $ 1,566 $ 1,214 $ 4,446 $ 3,995

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Basic and diluted net loss per share attributable to common stockholders: Numerator: Net loss $ (16,878 ) $ (17,222 ) $ (38,835 ) $ (1,862 ) Accretion of redeemable convertible preferred stock to redemption value — — — (11 ) Net loss attributable to common stockholders $ (16,878 ) $ (17,222 ) $ (38,835 ) $ (1,873 ) Denominator: Weighted average commons shares outstanding — basic and diluted 27,862,544 27,598,251 27,844,591 17,398,249 Net loss per share attributable to common stockholders — basic and diluted $ (0.61 ) $ (0.62 ) $ (1.39 ) $ (0.11 )
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share Attributable to Common Stockholders	The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated above because including them would have had an anti-dilutive effect: September 30, 2019 2018 Stock options to purchase common stock 5,512,379 4,509,041 Shares to be issued under the 2018 ESPP 78,714 — 5,591,093 4,509,041

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Summary of Components of Lease Expense	The components of the Company’s lease expense are as follows: Lease Costs Classification Three months ended September 30, 2019 Nine months ended September 30, 2019 Operating lease cost R&D Expense 575 1,733 G&A Expense 234 695 Variable lease costs (1) R&D Expense 191 532 G&A Expense 78 214 Total lease cost 1,078 3,174 Weighted-average remaining lease term (in months) 120.0 Weighted-average discount rate 10.5 % (1) Variable lease costs include certain additional charges for operating costs, including insurance, maintenance, taxes, utilities, and other costs incurred, which are billed based on both usage and as a percentage of the Company’s share of total square footage. Short term lease costs are immaterial.
Schedule of Maturities of Operating Lease Liabilities	As of September 30, 2019, the maturities of the Company’s operating lease liabilities were as follows: Year Ending December 31, 2019 800 2020 4,922 2021 5,861 2022 5,468 2023 5,410 Thereafter 37,573 Total future lease payments 60,034 Less: Interest (39,154 ) Present value of future lease payments (lease liability) $ 20,880
Schedule of Future Minimum Lease Payments	Future minimum lease payments for the Company’s operating leases as of December 31, 2018 were as follows: Year Ending December 31, 2019 2,546 2020 4,258 2021 5,176 2022 5,292 2023 5,376 Thereafter 37,573 $ 60,221

Nature of the Business - Additi

Nature of the Business - Additional Information (Details)	May 01, 2019USD ($)	Apr. 23, 2018USD ($)$ / sharesshares	Apr. 06, 2018	May 31, 2019USD ($)	Jan. 31, 2016shares	Jun. 30, 2018shares	Sep. 30, 2019USD ($)shares	Dec. 31, 2018USD ($)shares
Class Of Stock [Line Items]
State of incorporation							DE
Common stock, issued							27,882,756	27,772,600
Accumulated deficit | $							$ 105,641,000	$ 66,806,000
Operating expenses and capital expenditure requirements							12 months
Cash, cash equivalents and marketable securities | $							$ 111,804,000
Series A and A-1 Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock converted into common stock		16,863,624
Initial Public Offering
Class Of Stock [Line Items]
Issuance of common stock (in shares)		7,200,000
Shares issued, price per share | $ / shares		$ 15
Gross proceeds from issuance of common stock | $		$ 108,000,000
Net proceeds from issuance of common stock | $		$ 97,209,000
ATM Facility
Class Of Stock [Line Items]
Common stock, issued							0
Novartis Institutes for Biomedical Research, Inc. | Novartis Collaboration | Private Placement
Class Of Stock [Line Items]
Issuance of common stock (in shares)		766,666			766,666
Shares issued, price per share | $ / shares		$ 15
Net proceeds from issuance of common stock | $		$ 11,500,000
JonesTrading Institutional Services LLC | ATM Facility | Maximum
Class Of Stock [Line Items]
Gross proceeds from issuance of common stock | $	$ 30,000,000			$ 30,000,000
Percentage of gross proceeds of shares sold for compensation	3.00%
Common Stock
Class Of Stock [Line Items]
Reverse stock split, conversion ratio			0.4545
Common Stock | Initial Public Offering
Class Of Stock [Line Items]
Issuance of common stock (in shares)						7,200,000
Common Stock | Novartis Institutes for Biomedical Research, Inc. | Private Placement
Class Of Stock [Line Items]
Issuance of common stock (in shares)						766,666

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Jan. 01, 2019
Accounting Policies [Abstract]
Operating lease, right-of-use asset	$ 15,807	$ 16,672
Operating lease, right-of-use liabilities	$ 21,708

Marketable Securities - Summary

Marketable Securities - Summary of Fair Value of Available-for-sale Marketable Debt Securities by Type of Security (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 73,143	$ 76,042
Gross Unrealized Gains	140
Gross Unrealized Losses	(2)	(119)
Fair Value	73,281	75,923
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		10,276
Gross Unrealized Losses		(80)
Fair Value		10,196
U.S. Treasury Notes
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	57,211	62,866
Gross Unrealized Gains	92
Gross Unrealized Losses	(2)	(24)
Fair Value	57,301	62,842
U.S. Government Agency Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,932	2,900
Gross Unrealized Gains	48
Gross Unrealized Losses		(15)
Fair Value	$ 15,980	$ 2,885

Marketable Securities - Summa_2

Marketable Securities - Summary of Fair Value of Available-for-sale Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available For Sale Securities [Abstract]
Maturing in one year or less, Amortized Cost	$ 73,143	$ 76,042
Amortized Cost	73,143	76,042
Maturing in one year or less, Fair Value	73,281	75,923
Fair Value	$ 73,281	$ 75,923

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Available For Sale Securities [Abstract]
Investments in other-than-temporary decline in fair value	$ 0	$ 0

Fair Value of Financial Assets

Fair Value of Financial Assets - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	$ 101,020	$ 153,660
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	27,739	77,737
U.S. Treasury Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	57,301	62,842
U.S. Government Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	15,980	2,885
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis		10,196
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	27,739	77,737
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	27,739	77,737
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	73,281	75,923
Level 2 | U.S. Treasury Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	57,301	62,842
Level 2 | U.S. Government Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	$ 15,980	2,885
Level 2 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis		$ 10,196

Fair Value of Financial Asset_2

Fair Value of Financial Assets - Additional Information (Details) - USD ($)	Sep. 30, 2019	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair value assets transfers between level 1 to level 2	$ 0	$ 0
Fair value assets transfers between level 2 to level 1	0	0
Fair value assets transfers between level 1 to level 3	0	0
Fair value assets transfers between level 3 to level 1	0	0
Fair value assets transfers between level 2 to level 3	0	0
Fair value assets transfers between level 3 to level 2	$ 0	$ 0

Collaboration Agreement with _3

Collaboration Agreement with Novartis - Additional Information (Details) - USD ($)	Apr. 23, 2018	Feb. 28, 2018	Dec. 31, 2016	Jan. 31, 2016	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Preferred stock shares issued to related party					0			0		0
Proceeds from stock issued to related party in private placement									$ 11,500,000
Collaboration revenue - related party					$ 344,000	$ 1,730,000		$ 14,921,000	49,653,000
ASU 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party								14,921,000	49,653,000
Novartis
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment for reimbursement of manufacturing costs incurred								0	3,543,000
Novartis Collaboration
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from collaboration arrangement			$ 5,000,000
Revenue performance obligation					39,031,000			39,031,000
Novartis Collaboration | Novartis Institutes for Biomedical Research, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment for reimbursement of manufacturing costs incurred								0	$ 3,543,000
Collaboration revenue - related party					$ 344,000			14,921,000
Novartis Collaboration | Novartis Institutes for Biomedical Research, Inc. | ASU 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from collaboration arrangement		$ 45,000,000					$ 5,000,000
Novartis Collaboration | Novartis Institutes for Biomedical Research, Inc. | Up Front Payment Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from collaboration arrangement				$ 70,000,000
Novartis Collaboration | Novartis Institutes for Biomedical Research, Inc. | Milestone Payment
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestones payment								220,000,000
Novartis Collaboration | Novartis Institutes for Biomedical Research, Inc. | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of share holding				5.00%
Novartis Collaboration | Novartis Institutes for Biomedical Research, Inc. | Minimum | Milestone Payment
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestones payment								$ 500,000,000
Novartis Collaboration | Novartis Institutes for Biomedical Research, Inc. | Maximum | Option Purchase and Purchase Exercise Payment
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum aggregate amount of potential option purchase, option exercise and milestone payments to be received				$ 20,000,000
Novartis Collaboration | Series A One Redeemable Convertible Preferred Stock | Novartis Institutes for Biomedical Research, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Preferred stock shares issued to related party				2,000,000
Novartis Collaboration | Private Placement | Novartis Institutes for Biomedical Research, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock shares issued to related party	766,666			766,666
Share price				$ 15
Proceeds from stock issued to related party in private placement				$ 11,500,000

Collaboration Agreement with _4

Collaboration Agreement with Novartis - Schedule of Collaboration Revenue Related Party (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party	$ 344	$ 1,730	$ 14,921	$ 49,653
ASU 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party			$ 14,921	$ 49,653

Collaboration Agreement with _5

Collaboration Agreement with Novartis - Summary of Changes in Contract Liabilities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)
Change In Contract With Customer Asset And Liability [Abstract]
Deferred revenue - Beginning balance	$ 53,952
Deferred revenue - Deductions	(14,921)
Deferred revenue - Ending balance	$ 39,031

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock - Additional Information (Details)	Apr. 23, 2018shares
Series A and A-1 Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock converted into common stock	16,863,624

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) - Additional Information (Details)	May 01, 2019USD ($)	Apr. 23, 2018USD ($)$ / sharesshares	May 31, 2019USD ($)	Jan. 31, 2016shares	Sep. 30, 2019USD ($)Vote$ / sharesshares	Dec. 31, 2018$ / sharesshares
Subsidiary Sale Of Stock [Line Items]
Common stock, authorized | shares					150,000,000	150,000,000
Common stock, par value | $ / shares					$ 0.0001	$ 0.0001
Number of votes entitled by each share of common stock holder | Vote					1
Common stock voting rights					Each share of common stock entitles the holder to one vote
Dividends, declared or paid					$ 0
Total reserved | shares					17,361,676	6,083,202
Initial Public Offering
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock (in shares) | shares		7,200,000
Shares issued, price per share | $ / shares		$ 15
Gross proceeds from issuance of common stock		$ 108,000,000
Net proceeds from issuance of common stock		$ 97,209,000
JonesTrading Institutional Services LLC | ATM Facility | Maximum
Subsidiary Sale Of Stock [Line Items]
Gross proceeds from issuance of common stock	$ 30,000,000		$ 30,000,000
Novartis Institutes for Biomedical Research, Inc. | Private Placement | Novartis Collaboration
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock (in shares) | shares		766,666		766,666
Shares issued, price per share | $ / shares		$ 15
Net proceeds from issuance of common stock		$ 11,500,000

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Apr. 03, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost		$ 12,890
Unrecognized stock-based compensation cost, weighted-average period		2 years 14 days
Employee Stock Option | Non-Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock converted under option plan		278,735		317,957
2014 Plan | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of exercise price per share of stock options to fair market value of share of common stock		100.00%
Stock options granted expiry period		10 years
Weighted average grant-date fair value per share of stock options granted		$ 2.85		$ 7.47
2018 Stock Option and Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock to be issued	1,545,454
Percentage of authorized number of shares of common stock outstanding	4.00%
Number of shares of common stock converted under option plan		5,512,379		4,414,225
2018 Stock Option and Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock shares available for further issuance		1,314,753
2018 Stock Option and Incentive Plan | 2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock to be issued	256,818	534,544
Percentage of authorized number of shares of common stock outstanding	1.00%
Number of shares of common stock issued		0	0
2014 Plan and 2018 Plan | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted expiry period		10 years
Stock options granted vesting period		4 years

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity (Details) - 2018 Stock Option and Incentive Plan $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Outstanding beginning balance | shares	4,414,225
Number of Shares, Granted | shares	1,411,597
Number of Shares, Exercised | shares	(110,156)
Number of Shares, Forfeited | shares	(203,287)
Number of Shares, Outstanding ending balance | shares	5,512,379	4,414,225
Number of Shares, Options exercisable at June 30, 2019 | shares	2,591,780
Number of Shares, Vested and expected to vest at June 30, 2019 | shares	5,512,379
Weighted Average Exercise Price, Outstanding beginning balance | $ / shares	$ 6.79
Weighted Average Exercise Price, Granted | $ / shares	4.27
Weighted Average Exercise Price, Exercised | $ / shares	2.31
Weighted Average Exercise Price, Forfeited | $ / shares	6.94
Weighted Average Exercise Price, Outstanding ending balance | $ / shares	6.22	$ 6.79
Weighted Average Exercise Price, Options exercisable at June 30, 2019 | $ / shares	5.49
Weighted Average Exercise Price, Vested and expected to vest at June 30, 2019 | $ / shares	$ 6.22
Weighted Average Remaining Contractual Term (in years), Outstanding	8 years 18 days	8 years 3 months 14 days
Weighted Average Remaining Contractual Term (in years), Options exercisable	7 years 4 months 13 days
Weighted Average Remaining Contractual Term (in years), Vested and expected to vest	8 years 18 days
Aggregate Intrinsic Value | $	$ 437	$ 2,031
Aggregate Intrinsic Value, Options exercisable at June 30, 2019 | $	427
Aggregate Intrinsic Value, Vested and expected to vest at June 30, 2019 | $	$ 437

Stock-Based Awards - Summary _2

Stock-Based Awards - Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Stock Awards (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 1,566	$ 1,214	$ 4,446	$ 3,995
Research and Development Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	596	470	1,767	2,111
General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 970	$ 744	$ 2,679	$ 1,884

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (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	$ (16,878)	$ (17,758)	$ (4,199)	$ (17,222)	$ (15,852)	$ 31,212	$ (38,835)	$ (1,862)
Accretion of redeemable convertible preferred stock to redemption value								(11)
Net loss attributable to common stockholders	$ (16,878)			$ (17,222)			$ (38,835)	$ (1,873)
Denominator:
Weighted average commons shares outstanding — basic and diluted	27,862,544			27,598,251			27,844,591	17,398,249
Net loss per share attributable to common stockholders— basic and diluted	$ (0.61)			$ (0.62)			$ (1.39)	$ (0.11)

Net Loss per Share - Schedule_2

Net Loss per Share - Schedule of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss per Share Attributable to Common Stockholders (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	5,591,093	4,509,041
Employee Stock Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	5,512,379	4,509,041
2018 ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	78,714

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Income tax provision or benefit	$ 0	$ 0	$ 0	$ 0
Interest and penalties accrued	$ 0		$ 0		$ 0
Income tax examination, description			The Company is currently under examination by the Internal Revenue Service ("IRS") for the period ended December 31, 2016. The Company's tax years are still open under statute from 2015 to present. All years may be examined to the extent the tax credit or net operating loss carryforwards are used in future periods
Earliest Tax Year
Operating Loss Carryforwards [Line Items]
Tax year remain open			2015
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Income tax examination, year under examination			2016

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Lease Agreements [Line Items]
Cash paid for lease liabilities	$ 1,068		$ 3,137
Total rent expense		$ 711		$ 2,048
Operating sublease, expiration period			2018-03
Sublease payments received from third-party tenant		$ 3		$ 231
MASSACHUSETTS
Lease Agreements [Line Items]
Renewal terms of lease	5 years		5 years
MASSACHUSETTS | Minimum
Lease Agreements [Line Items]
Lease term	1 year		1 year
Operating lease, discount rate	9.50%		9.50%
MASSACHUSETTS | Maximum
Lease Agreements [Line Items]
Lease term	10 years		10 years
Operating lease, discount rate	10.50%		10.50%

Leases - Summary of Components

Leases - Summary of Components of Lease Expense (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)		Sep. 30, 2019USD ($)
Lease Agreements [Line Items]
Operating lease cost			$ 865
Total lease cost	$ 1,078		$ 3,174
Weighted-average remaining lease term (in months)	120 months		120 months
Weighted-average discount rate	10.50%		10.50%
Research and Development Expenses
Lease Agreements [Line Items]
Operating lease cost	$ 575		$ 1,733
Variable lease costs	191	[1]	532	[1]
General and Administrative Expenses
Lease Agreements [Line Items]
Operating lease cost	234		695
Variable lease costs	$ 78		$ 214
[1]	Variable lease costs include certain additional charges for operating costs, including insurance, maintenance, taxes, utilities, and other costs incurred, which are billed based on both usage and as a percentage of the Company’s share of total square footage. Short term lease costs are immaterial.

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Operating Lease Liabilities (Details) $ in Thousands	Sep. 30, 2019USD ($)
Leases [Abstract]
2019	$ 800
2020	4,922
2021	5,861
2022	5,468
2023	5,410
Thereafter	37,573
Total future lease payments	60,034
Less: Interest	(39,154)
Present value of future lease payments (lease liability)	$ 20,880

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Leases [Abstract]
2019	$ 2,546
2020	4,258
2021	5,176
2022	5,292
2023	5,376
Thereafter	37,573
Total operating leases	$ 60,221

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	Apr. 23, 2018	Jan. 31, 2016	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Preferred stock shares issued to related party			0		0		0
Proceeds from private placement						$ 11,500,000
Collaboration revenue			$ 344,000	$ 1,730,000	$ 14,921,000	49,653,000
Novartis Institutes for Biomedical Research, Inc. | Novartis Collaboration
Related Party Transaction [Line Items]
Collaboration revenue			344,000		14,921,000
Amounts due from related party			0	0	0	0
Payment for reimbursement of manufacturing costs incurred					0	3,543,000
Novartis Institutes for Biomedical Research, Inc. | Novartis Collaboration | Minimum
Related Party Transaction [Line Items]
Percentage of share holding		5.00%
Novartis Institutes for Biomedical Research, Inc. | Novartis Collaboration | Series A One Redeemable Convertible Preferred Stock
Related Party Transaction [Line Items]
Preferred stock shares issued to related party		2,000,000
Gross proceeds from issuance of preference stock		$ 13,500,000
Novartis Institutes for Biomedical Research, Inc. | Novartis Collaboration | Private Placement
Related Party Transaction [Line Items]
Common stock shares issued to related party	766,666	766,666
Share price		$ 15
Proceeds from private placement		$ 11,500,000
Vaccinex, Inc.
Related Party Transaction [Line Items]
Due to related party			0	66,000	0	66,000
Vaccinex, Inc. | Research and Development Expenses
Related Party Transaction [Line Items]
Payments to related party			$ 425,000	$ 64,000	$ 602,000	$ 133,000