Surface Oncology (SURF) 10-Q 13 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 08, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	SURF
Entity Registrant Name	SURFACE ONCOLOGY, INC.
Entity Central Index Key	1,718,108
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		27,681,724

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 41,592	$ 22,455
Marketable securities	131,783	40,854
Restricted cash		85
Prepaid expenses and other current assets	4,538	7,936
Total current assets	177,913	71,330
Property and equipment, net	7,099	7,326
Restricted cash	1,198	1,000
Deferred offering costs		1,784
Other assets	68	14
Total assets	186,278	81,454
Current liabilities:
Accounts payable	4,228	3,215
Accrued expenses and other current liabilities	7,298	9,843
Deferred revenue - related party	15,760	9,837
Deferred rent	352	489
Total current liabilities	27,638	23,384
Deferred revenue - related party, non-current	47,957	72,268
Deferred rent, non-current	4,663	4,599
Total liabilities	80,258	100,251
Commitments and contingencies (Note 11)
Redeemable convertible preferred stock (Series A and A-1), $0.0001 par value; no shares authorized, issued and outstanding at September 30, 2018 and 37,100,000 shares authorized, issued and outstanding at December 31, 2017		48,517
Stockholders’ equity (deficit):
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at September 30, 2018 and no shares authorized at December 31, 2017; no shares issued and outstanding at September 30, 2018 and December 31, 2017
Common stock, $0.0001 par value; 150,000,000 and 53,000,000 shares authorized at September 30, 2018 and December 31, 2017, respectively; 27,607,213 and 2,686,350 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	3
Additional paid-in capital	168,278	6,877
Accumulated other comprehensive loss	(190)	(246)
Accumulated deficit	(62,071)	(73,945)
Total stockholders’ equity (deficit)	106,020	(67,314)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity	$ 186,278	$ 81,454

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Redeemable convertible preferred stock , par vale	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock ,authorized	0	37,100,000
Redeemable convertible preferred stock , issued	0	37,100,000
Redeemable convertible preferred stock , outstanding	0	37,100,000
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, authorized	5,000,000	0
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized	150,000,000	53,000,000
Common stock, issued	27,607,213	2,686,350
Common stock, outstanding	27,607,213	2,686,350

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Collaboration revenue - related party	$ 1,730,000	$ 2,480,000	$ 49,653,000	$ 10,347,000
Operating expenses:
Research and development	15,783,000	12,101,000	41,971,000	31,501,000
General and administrative	3,977,000	4,651,000	11,252,000	8,201,000
Total operating expenses	19,760,000	16,752,000	53,223,000	39,702,000
Loss from operations	(18,030,000)	(14,272,000)	(3,570,000)	(29,355,000)
Interest and other income (expense), net	808,000	208,000	1,708,000	470,000
Loss before income taxes	(17,222,000)	(14,064,000)	(1,862,000)	(28,885,000)
Provision for income taxes	0	(341,000)	0	(719,000)
Net loss	(17,222,000)	(14,405,000)	(1,862,000)	(29,604,000)
Accretion of redeemable convertible preferred stock to redemption value		(10,000)	(11,000)	(30,000)
Net loss attributable to common stockholders	$ (17,222,000)	$ (14,415,000)	$ (1,873,000)	$ (29,634,000)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.62)	$ (5.75)	$ (0.11)	$ (12.11)
Weighted average common shares outstanding—basic and diluted	27,598,251	2,506,150	17,398,249	2,446,156
Comprehensive loss:
Net loss	$ (17,222,000)	$ (14,405,000)	$ (1,862,000)	$ (29,604,000)
Other comprehensive income:
Unrealized gain on marketable securities, net of tax of $0	43,000	43,000	56,000	176,000
Comprehensive loss	$ (17,179,000)	$ (14,362,000)	$ (1,806,000)	$ (29,428,000)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Income Statement [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	Initial Public Offering	Private PlacementNovartis Institutes for Biomedical Research, Inc.	Series A and A-1 Redeemable Convertible Preferred Stock	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 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			37,100,000
Temporary equity beginning balance at Dec. 31, 2017	$ 48,517			$ 48,517
Beginning balance, share at Dec. 31, 2017	2,686,350				2,686,350
Issuance of common stock upon exercise of stock options	$ 183							183
Issuance of common stock upon exercise of stock options, share					107,508
Repurchases of unvested restricted stock, shares					(16,935)
Stock-based compensation expense	3,995							3,995
Accretion of redeemable convertible preferred stock to redemption value				$ 11
Accretion of redeemable convertible preferred stock to redemption value	(11)							(11)
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
Adjustment due to the adoption of ASC 606	13,736											13,736
Unrealized gain on marketable securities	56										56
Net loss	(1,862)											(1,862)
Ending balance at Sep. 30, 2018	$ 106,020
Temporary equity ending balance, share at Sep. 30, 2018	0
Ending balance, share at Sep. 30, 2018	27,607,213
Beginning balance at Jun. 30, 2018	$ 106,020				$ 3			$ 168,278			$ (190)	$ (62,071)
Beginning balance, share at Jun. 30, 2018					27,607,213
Net loss	(17,222)
Ending balance at Sep. 30, 2018	$ 106,020
Temporary equity ending balance, share at Sep. 30, 2018	0
Ending balance, share at Sep. 30, 2018	27,607,213

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (1,862)	$ (29,604)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization expense	982	657
Stock-based compensation expense	3,995	4,036
Net amortization of premiums and discounts on marketable securities	(207)	407
Realized losses on marketable securities		2
Loss on disposal of property and equipment	13	35
Deferred income tax benefit		(3,156)
Changes in operating assets and liabilities:
Amounts due from related party		5,000
Prepaid expenses and other current assets	3,398	1,156
Other assets	(54)	(19)
Accounts payable	1,144	1,062
Accrued expenses and other current liabilities	(1,964)	2,517
Deferred rent	(73)	297
Deferred revenue - related party	(4,652)	19,654
Net cash provided by operating activities	720	2,044
Cash flows from investing activities:
Purchases of property and equipment	(896)	(1,395)
Purchases of marketable investments	(107,258)
Proceeds from sales or maturities of marketable securities	16,592	20,890
Net cash (used in) provided by investing activities	(91,562)	19,495
Cash flows from financing activities:
Payments of initial public offering costs	(2,031)	(253)
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	183	39
Net cash provided by (used in) financing activities	110,092	(214)
Net increase in cash and cash equivalents and restricted cash	19,250	21,325
Cash and cash equivalents and restricted cash at beginning of period	23,540	11,080
Cash and cash equivalents and restricted cash at end of period	42,790	32,405
Supplemental disclosure of non-cash investing and financing activities:
Accretion of redeemable convertible preferred stock to redemption value	11	30
Purchases of property and equipment included in accounts payable and accrued expenses	$ 322	246
Deferred offering costs included in accrued expenses		78
Reclassification of deposit liability for restricted stock upon vesting of shares		36
Landlord incentives for construction of leasehold improvements recorded as deferred rent		$ 2,377

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2018
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 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 (see Note 6). 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. 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, 2018, the Company had an accumulated deficit of $62,071. The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. As of November 13, 2018, the filing date of this Quarterly Report on Form 10-Q, the Company expects that its cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least the next 12 months from the date that the condensed consolidated financial statements are issued. 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 offerings, 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, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying 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 1 to the financial statements included in the Company’s final prospectus for its initial public offering of its common stock filed with the Securities and Exchange Commission (the “SEC”) pursuant to Rule 424(b)(4) of the Securities Act on April 18, 2018, which the Company refers to as the Prospectus, except for the Company’s adoption of the new standards 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 common stock and 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. Unaudited Interim Financial Information The accompanying condensed consolidated balance sheet as of September 30, 2018, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2018 and 2017, the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 and 2017, and the condensed consolidated statement of redeemable convertible preferred stock and stockholders’ equity (deficit) for the nine months ended September 30, 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, 2018 and the results of its operations and its cash flows for the nine months ended September 30, 2018 and 2017. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2018 and 2017 are also unaudited. The results for the three and nine months ended September 30, 2018 are not necessarily indicative of results to be expected for the year ending December 31, 2018, any other interim periods, or any future year period. Recently Adopted Accounting Pronouncements Revenue from Contracts with Customers I n May 2014, the Financial Accounting Standards Board ( FAS ) issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which delayed the effective date of the new standard from January 1, 2017 to January 1, 2018. The FASB also agreed to allow entities to choose to adopt the standard as of the original effective date. In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations , which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing , which clarifies how a company identifies promised goods or services and clarifies whether an entity’s promise to grant a license provides a customer with either a right to use the entity’s intellectual property (which is satisfied at a point in time) or a right to access the entity’s intellectual property (which is satisfied over time). In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients related to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. In December 2016 the FASB issued ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers , which amends certain narrow aspects of the guidance issued in ASU 2014-09 including guidance related to the disclosure of remaining performance obligations and prior-period performance obligations, as well as other amendments to the guidance on loan guarantee fees, contract costs, refund liabilities, advertising costs and the clarification of certain examples. ASU 2016-08, ASU 2016-10 and ASU 2016-12 have the same effective dates and transition requirements as ASU 2014-09, all of which collectively are herein referred to as Revenue ASUs. The Company adopted the Revenue ASUs effective January 1, 2018 using the modified retrospective method. Under the modified retrospective method, the cumulative effect of adopting the Revenue ASUs is recognized as an adjustment to deferred revenue and accumulated deficit. Under ASC 606, the Company will recognize revenue from its collaboration agreement with Novartis (see Note 5) earlier during the performance period as a result of applying the cost-to-cost method, in contrast to recognizing revenue on a straight-line basis over the estimated ten-year performance period under the previous standard. The following reflects the impact of the cumulative effect of the accounting changes upon the adoption of the Revenue ASUs (in thousands): Condensed Consolidated Balance Sheets December 31, 2017 Cumulative Effect January 1, 2018 Deferred revenue - related party, current and net of current portions $ 82,105 $ (13,736 ) $ 68,369 Accumulated deficit (73,945 ) 13,736 (60,209 ) September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Deferred revenue - related party $ 15,760 $ 14,421 $ 1,339 Deferred revenue, net of current portion - related party 47,957 87,830 (39,873 ) Accumulated deficit (62,071 ) (86,870 ) 24,799 Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) Three months ended September 30, 2018 Nine months ended September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Under Topic 606 Under Topic 605 Effect of Change Collaboration revenue - related party $ 1,730 $ 3,634 $ (1,904 ) $ 49,653 $ 24,854 $ 24,799 Income from operations (18,030 ) (16,126 ) (1,904 ) (3,570 ) (28,369 ) 24,799 Net income (17,222 ) (15,318 ) (1,904 ) (1,862 ) (26,661 ) 24,799 Comprehensive income (17,179 ) (15,275 ) (1,904 ) (1,806 ) (26,605 ) 24,799 Condensed Consolidated Statements of Cash Flows Nine months ended September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Net income $ (1,862 ) $ (26,661 ) $ 24,799 Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Deferred revenue - related party (4,652 ) 20,147 (24,799 ) During the nine months ended September 30, 2018, the Company adopted ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows: Restricted Cash (“ASU 2016-18”) As of September 30, 2018 2017 Cash and cash equivalents $ 41,592 $ 31,320 Restricted cash included in current assets — 85 Restricted cash included in non-current assets 1,198 1,000 Total cash, cash equivalents, and restricted cash shown in the statement of cash flows $ 42,790 $ 32,405 Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases “Codification Improvements to Topic 842, Leases” 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 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 new standard will be effective beginning January 1, 2019 and early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2018-07 will have on its results of operations. 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, 2018
Marketable Securities [Abstract]
Marketable Securities	3. Marketable Securities As of September 30, 2018, the fair value of available-for-sale marketable debt securities by type of security was as follows: September 30, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable debt securities: U.S. Treasury notes $ 107,651 $ — $ (55 ) $ 107,596 U.S. Government agency bonds 2,900 — (23 ) 2,877 Corporate bonds 21,422 — (112 ) 21,310 $ 131,973 $ — $ (190 ) $ 131,783 The amortized cost and fair value of the Company’s available-for-sale debt securities by contractual maturity are summarized as follows: September 30, 2018 Amortized Cost Fair Value Maturing in one year or less $ 131,973 $ 131,783 $ 131,973 $ 131,783 As of December 31, 2017, the fair value of available-for-sale marketable debt securities by type of security was as follows: December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable debt securities: U.S. government agency bonds $ 7,300 $ — $ (38 ) $ 7,262 Corporate bonds 33,800 — (208 ) $ 33,592 $ 41,100 $ — $ (246 ) $ 40,854 The amortized cost and fair value of the Company’s available-for-sale securities by contractual maturity are summarized as follows: December 31, 2017 Amortized Cost Fair Value Maturing in one year or less $ 27,769 $ 27,672 Maturing after one year but less than two years 13,331 13,182 $ 41,100 $ 40,854 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, 2018 and December 31, 2017.

Fair Value of Financial Assets

Fair Value of Financial Assets	9 Months Ended
	Sep. 30, 2018
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, 2018 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 30,856 $ — $ — $ 30,856 Marketable securities: U.S. Treasury notes — 107,596 — 107,596 U.S. Government agency bonds — 2,877 — 2,877 Corporate bonds — 21,310 — 21,310 $ 30,856 $ 131,783 $ — $ 162,639 Fair Value Measurements as of December 31, 2017 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 17,409 $ — $ — $ 17,409 Marketable securities: U.S. government agency bonds — 7,262 — 7,262 Corporate bonds — 33,592 — 33,592 $ 17,409 $ 40,854 $ — $ 58,263 As of September 30, 2018 and December 31, 2017, 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, 2018 and 2017, 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, 2018
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 “Novartis Collaboration”), which was subsequently amended in May 2016, July 2017, September 2017 and October 2018 (the “October 2018 Amendment”). Pursuant to the Novartis Collaboration, the Company granted Novartis a worldwide exclusive license to research, develop, manufacture and commercialize antibodies that target CD73, along with the right to purchase exclusive option rights (each an “Option”) for up to four specified targets (each an “Option Target”) to obtain certain development, manufacturing and commercialization rights. Novartis may exercise up to three purchased Options. Under the Novartis Collaboration, Novartis initially had the ability to exclusively license the development and manufacturing rights for up to four targets (inclusive of CD73). Of these, the Company would retain the U.S. commercial rights to two of such targets. The Novartis Collaboration 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 Novartis Collaboration 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 principal stockholder of the Company. In January 2016, the Company entered into the Novartis Collaboration 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, 2018 the Company made a payment of $3,437 to Novartis for the reimbursement of manufacturing costs incurred by Novartis prior to December 31, 2017. During the nine months ended September 30, 2017, the Company made no cash payments to Novartis related to the Novartis Collaboration. Research on Targets Under the Novartis Collaboration, 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. Novartis also has the right, but not the obligation, to conduct research at its own cost on antibodies that bind to CD73 in accordance with the terms of the Novartis Collaboration. 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 Novartis Collaboration will terminate. Novartis may exercise up to a total of three purchased Options. Each exercised Option will be designated as either a regional or global option, with each such designation determining the development and commercialization rights between the parties with respect to such Option Target, corresponding antibody candidates and licensed products, as summarized below. The Company had the ability to designate the first Option as either regional or global. Of the remaining two Options, the Company and Novartis each have the ability to designate the geographical scope of one Option. 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, and as of December 31, 2017, there were three remaining Options that may be purchased by Novartis. 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 Novartis Collaboration. Accordingly, as of September 30, 2018, Novartis had two Options remaining eligible for purchase, each of which can be exercised. 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 right, 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 Novartis Collaboration 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 Novartis Collaboration. 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 Novartis 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 Novartis Collaboration 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 $67,500 in option purchase and option exercise payments, of which $5,000 has been received Termination Unless terminated earlier, the Novartis Collaboration will continue in effect until neither the Company nor Novartis is researching, developing, manufacturing or commercializing any antibody candidates or licensed products under the Novartis Collaboration. Novartis may terminate the Novartis Collaboration on a target-by-target basis for any reason upon prior notice to the Company within a specified time period. However, Novartis cannot terminate the Novartis Collaboration with respect to CD73 for a certain period of time following the effective date. Either party may terminate the Novartis Collaboration 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 for the Company’s material breach or insolvency, 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 On January 1, 2018 the Company adopted ASC 606 under the modified retrospective method. Prior to January 1, 2018 the Company accounted for the collaboration agreement with Novartis under ASC 605-25, Multiple Element Arrangements. Accounting under ASC 605 The Company determined that the deliverables under the Novartis Collaboration included (i) the worldwide exclusive license to CD73 antibody candidates, which was delivered to Novartis in January 2016 upon entering into the agreement and (ii) the Company’s research and development and joint steering committee participation obligations under the agreement. The Company also determined that none of these deliverables have standalone value due to the specialized nature of the services to be provided by the Company in connection with the Novartis Collaboration. Therefore, at the inception of the arrangement, the Company concluded that the deliverables were not separable and, accordingly, the Company treated the license and undelivered services as a single unit of accounting and recognized revenue on a straight-line basis over the period that the Company expected to complete its performance obligations under the agreement, which was estimated to be ten years. Accordingly, the Company recognized the upfront payment and milestone payments received over the estimated ten-year period of performance. In December 2016, Novartis purchased an exclusive option right to antibodies that bind to CD47 for $5,000. At that time, the Company concluded that the license and other obligations underlying the exclusive option right held by Novartis represented separate and additional deliverables that Novartis may receive from the Company in future periods. In December 2017, the Company included $5,000 in deferred revenue for the option purchase payment. In March 2018, Novartis decided not to exercise this option. Accounting under ASC 606 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 GLP toxicology study report for SRF373. 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. The Company recognized $24,746 as collaboration revenue – related party in the nine months ended September 30, 2018, based on the ratio of actual costs incurred as of the milestone achievement date to the total estimated costs with respect to performing research on antibodies that bind to CD73 and other specified targets under the Novartis Collaboration. The remaining unrecognized amount of $20,254 is recorded as deferred revenue – related party as of September 30, 2018 and will subsequently be recognized as revenue over the performance period in proportion to the costs incurred under the Novartis Collaboration. 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 Novartis Collaboration. 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, 2018 and 2017, the Company recognized the following totals of collaboration revenue – related party: Three months ended September 30, 2018 Nine months ended September 30, 2018 2018 2017 2018 2017 Collaboration revenue - related party $ 1,730 $ 2,480 $ 49,653 $ 10,347 The following table presents changes in the Company’s contract assets and liabilities during the nine months ended September 30, 2018 (in thousands): December 31, 2017 Additions Deductions September 30, 2018 Contract Liabilities (1) Total deferred revenue - related party $ 82,105 $ 45,000 $ (63,388 ) $ 63,717 (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 and cumulative catch-up adjustment recognized upon adoption of ASC 606 on January 1, 2018. During and nine months ended September 30, 2018 and $19,908, respectively, of revenue 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 are partially unsatisfied was The Company

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2018
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, 2018
Equity [Abstract]
Stockholders' Equity (Deficit)	7. Stockholders’ Equity (Deficit) Common Stock As of September 30, 2018 and December 31, 2017, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 150,000,000 and 53,000,000 shares, respectively, 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 the Redeemable Convertible Preferred Stock. When dividends are declared on shares of common stock, the Company must declare at the same time a dividend payable to the holders of Redeemable Convertible Preferred Stock equivalent to the dividend amount they would receive if each preferred share were converted into common stock. The Company may not pay dividends to common stockholders until all dividends accrued or declared but unpaid on the Redeemable Convertible Preferred Stock have been paid in full. No dividends have been declared or paid by the Company through September 30, 2018. As of September 30, 2018 and December 31, 2017, the Company had reserved 6,248,589 and 20,703,575 shares, respectively, of common stock for the conversion of the outstanding shares of Redeemable Convertible Preferred Stock, the exercise of outstanding stock options and the number of shares remaining available for future grant under the Company’s 2014 Stock Incentive Plan and 2018 Stock Option and Incentive Plan. 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, 2018
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. The total number of shares of common stock that may be issued under the 2014 Plan was 4,489,839 shares as of December 31, 2017. On February 12, 2018, the Company effected an increase in the total number of shares of the Company’s common stock reserved for issuance under the 2014 Plan from 4,489,839 shares to 4,498,930 shares. On March 2, 2018, the Company effected an increase in the total number of shares of the Company’s common stock reserved for issuance under the 2014 Plan from 4,498,930 shares to 5,089,839 shares. On March 9, 2018, the Company effected an increase in the total number of shares of the Company’s common stock reserved for issuance under the 2014 Plan from 5,089,839 shares to 5,203,730 shares. As of September 30, 2018 all remaining shares available under the 2014 Plan were transferred to the 2018 Plan. As of December 31, 2017, 733,060 shares were available for future issuance under the 2014 Plan. 2018 Stock Option and Incentive Plan On April 3, 2018, the Company’s stockholders approved the 2018 Stock Option and Incentive Plan (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 is 1,545,454, plus the shares of common stock remaining available for issuance under the 2014 Plan, which shall be cumulatively increased on January 1, 2019 and each January 1 thereafter 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, 2018 1,482,730 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, 2018: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding as of December 31, 2017 3,106,891 $ 3.68 8.69 $ 14,361 Granted 1,723,048 11.28 Exercised (107,508 ) 1.70 Forfeited (213,390 ) 5.46 Outstanding as of September 30, 2018 4,509,041 $ 6.54 8.25 $ 18,775 Options exercisable at September 30, 2018 1,663,869 $ 3.91 7.08 $ 10,683 The weighted average grant-date fair value per share of stock options granted during the nine months ended September 30, 2018 and December 31, 2017 was $7.48 and $3.72, respectively. As of September 30, 2018 and December 31, 2017, there were outstanding stock options held by non-employees for the purchase of 493,964 and 369,645 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 reserved for issuance under this plan. In addition, the number of shares of common stock that may be issued under the ESPP will automatically increase on January 1, 2019, and 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. 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 income (loss): Nine months ended September 30, 2018 2017 Research and development expenses $ 2,111 $ 1,434 General and administrative expenses 1,884 2,602 $ 3,995 $ 4,036 As of September 30, 2018, the Company had an aggregate of $15,174 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 3.07 years.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2018
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, 2018 Nine months ended September 30, 2018 2018 2017 2018 2017 Basic and diluted net loss per share attributable to common stockholders: Numerator: Net loss $ (17,222 ) $ (14,405 ) $ (1,862 ) $ (29,604 ) Accretion of redeemable convertible preferred stock to redemption value — (10 ) (11 ) (30 ) Net loss attributable to common stockholders $ (17,222 ) $ (14,415 ) $ (1,873 ) $ (29,634 ) Denominator: Weighted average commons shares outstanding—basic and diluted 27,598,251 2,506,150 17,398,249 2,446,156 Net loss per share attributable to common stockholders—basic and diluted $ (0.62 ) $ (5.75 ) $ (0.11 ) $ (12.11 ) 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, 2018 2017 Redeemable convertible preferred shares (as converted to common stock) — 16,863,624 Stock options to purchase common stock 4,509,041 3,121,147 4,509,041 19,984,771

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes During the three and nine months ended September 30, 2018, the Company recorded no provision from income taxes because the Company is forecasting a loss for the year ended December 31, 2018. During the three and nine months ended September 30, 2017, the Company recorded an income tax provision of $341 and $719, respectively, which was primarily due to the federal and state income tax treatment of the payments received under the Novartis Collaboration. Prepaid income taxes of $923 and $6,657 at September 30, 2018 and December 31, 2017, respectively, were included in prepaid expenses and other current assets on the condensed consolidated balance sheet and consist primarily of amounts receivable under a refund claim filed with the state authorities as well as amounts paid to the Internal Revenue Service that will be applied to income taxes due in the future. The Company’s preliminary estimate of the Tax Cuts and Jobs Act of 2017, or TCJA, and the remeasurement of its deferred tax assets and liabilities is subject to the finalization of management’s analysis related to certain matters, such as developing interpretations of the provisions of the TCJA, changes to certain estimates and the filing of the Company’s tax returns. U.S. Treasury regulations, administrative interpretations or court decisions interpreting the TCJA may require further adjustments and changes in its estimates. The final determination of the TCJA and the remeasurement of the Company’s deferred assets and liabilities will be completed as additional information becomes available, but no later than one year from the enactment of the TCJA. For the nine months ended September 30, 2018, there were no changes to management’s analysis originally performed as of December 31, 2017.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Legal Proceedings The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to its legal proceedings. Lease Amendment In May 2018, the Company executed an amendment to lease an additional 33,529 square feet for a term of 10 years at 50 Hampshire The Company will pay annual rent of $71.00 per rentable square foot for the first year, with increases of $1.00 per rentable square foot for the remainder of the term.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	12. Related Party Transactions 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, 2018, the Company incurred an expense payable to Vaccinex for $66 and $199, respectively, as a technology access fee upon entering into the agreement and project initiation expenses. No amounts were due by the Company to Vaccinex as of December 31, 2017.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying 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 1 to the financial statements included in the Company’s final prospectus for its initial public offering of its common stock filed with the Securities and Exchange Commission (the “SEC”) pursuant to Rule 424(b)(4) of the Securities Act on April 18, 2018, which the Company refers to as the Prospectus, except for the Company’s adoption of the new standards 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 common stock and 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.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying condensed consolidated balance sheet as of September 30, 2018, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2018 and 2017, the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 and 2017, and the condensed consolidated statement of redeemable convertible preferred stock and stockholders’ equity (deficit) for the nine months ended September 30, 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, 2018 and the results of its operations and its cash flows for the nine months ended September 30, 2018 and 2017. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2018 and 2017 are also unaudited. The results for the three and nine months ended September 30, 2018 are not necessarily indicative of results to be expected for the year ending December 31, 2018, any other interim periods, or any future year period.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements Revenue from Contracts with Customers I n May 2014, the Financial Accounting Standards Board ( FAS ) issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which delayed the effective date of the new standard from January 1, 2017 to January 1, 2018. The FASB also agreed to allow entities to choose to adopt the standard as of the original effective date. In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations , which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing , which clarifies how a company identifies promised goods or services and clarifies whether an entity’s promise to grant a license provides a customer with either a right to use the entity’s intellectual property (which is satisfied at a point in time) or a right to access the entity’s intellectual property (which is satisfied over time). In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients related to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. In December 2016 the FASB issued ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers , which amends certain narrow aspects of the guidance issued in ASU 2014-09 including guidance related to the disclosure of remaining performance obligations and prior-period performance obligations, as well as other amendments to the guidance on loan guarantee fees, contract costs, refund liabilities, advertising costs and the clarification of certain examples. ASU 2016-08, ASU 2016-10 and ASU 2016-12 have the same effective dates and transition requirements as ASU 2014-09, all of which collectively are herein referred to as Revenue ASUs. The Company adopted the Revenue ASUs effective January 1, 2018 using the modified retrospective method. Under the modified retrospective method, the cumulative effect of adopting the Revenue ASUs is recognized as an adjustment to deferred revenue and accumulated deficit. Under ASC 606, the Company will recognize revenue from its collaboration agreement with Novartis (see Note 5) earlier during the performance period as a result of applying the cost-to-cost method, in contrast to recognizing revenue on a straight-line basis over the estimated ten-year performance period under the previous standard. The following reflects the impact of the cumulative effect of the accounting changes upon the adoption of the Revenue ASUs (in thousands): Condensed Consolidated Balance Sheets December 31, 2017 Cumulative Effect January 1, 2018 Deferred revenue - related party, current and net of current portions $ 82,105 $ (13,736 ) $ 68,369 Accumulated deficit (73,945 ) 13,736 (60,209 ) September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Deferred revenue - related party $ 15,760 $ 14,421 $ 1,339 Deferred revenue, net of current portion - related party 47,957 87,830 (39,873 ) Accumulated deficit (62,071 ) (86,870 ) 24,799 Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) Three months ended September 30, 2018 Nine months ended September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Under Topic 606 Under Topic 605 Effect of Change Collaboration revenue - related party $ 1,730 $ 3,634 $ (1,904 ) $ 49,653 $ 24,854 $ 24,799 Income from operations (18,030 ) (16,126 ) (1,904 ) (3,570 ) (28,369 ) 24,799 Net income (17,222 ) (15,318 ) (1,904 ) (1,862 ) (26,661 ) 24,799 Comprehensive income (17,179 ) (15,275 ) (1,904 ) (1,806 ) (26,605 ) 24,799 Condensed Consolidated Statements of Cash Flows Nine months ended September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Net income $ (1,862 ) $ (26,661 ) $ 24,799 Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Deferred revenue - related party (4,652 ) 20,147 (24,799 ) During the nine months ended September 30, 2018, the Company adopted ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows: Restricted Cash (“ASU 2016-18”) As of September 30, 2018 2017 Cash and cash equivalents $ 41,592 $ 31,320 Restricted cash included in current assets — 85 Restricted cash included in non-current assets 1,198 1,000 Total cash, cash equivalents, and restricted cash shown in the statement of cash flows $ 42,790 $ 32,405
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases “Codification Improvements to Topic 842, Leases” 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 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 new standard will be effective beginning January 1, 2019 and early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2018-07 will have on its results of operations. 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.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Impact of Cumulative Effect of Accounting Changes Upon Adoption of the Revenue ASUs	The Company adopted the Revenue ASUs effective January 1, 2018 using the modified retrospective method. Under the modified retrospective method, the cumulative effect of adopting the Revenue ASUs is recognized as an adjustment to deferred revenue and accumulated deficit. Under ASC 606, the Company will recognize revenue from its collaboration agreement with Novartis (see Note 5) earlier during the performance period as a result of applying the cost-to-cost method, in contrast to recognizing revenue on a straight-line basis over the estimated ten-year performance period under the previous standard. The following reflects the impact of the cumulative effect of the accounting changes upon the adoption of the Revenue ASUs (in thousands): Condensed Consolidated Balance Sheets December 31, 2017 Cumulative Effect January 1, 2018 Deferred revenue - related party, current and net of current portions $ 82,105 $ (13,736 ) $ 68,369 Accumulated deficit (73,945 ) 13,736 (60,209 ) September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Deferred revenue - related party $ 15,760 $ 14,421 $ 1,339 Deferred revenue, net of current portion - related party 47,957 87,830 (39,873 ) Accumulated deficit (62,071 ) (86,870 ) 24,799 Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) Three months ended September 30, 2018 Nine months ended September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Under Topic 606 Under Topic 605 Effect of Change Collaboration revenue - related party $ 1,730 $ 3,634 $ (1,904 ) $ 49,653 $ 24,854 $ 24,799 Income from operations (18,030 ) (16,126 ) (1,904 ) (3,570 ) (28,369 ) 24,799 Net income (17,222 ) (15,318 ) (1,904 ) (1,862 ) (26,661 ) 24,799 Comprehensive income (17,179 ) (15,275 ) (1,904 ) (1,806 ) (26,605 ) 24,799 Condensed Consolidated Statements of Cash Flows Nine months ended September 30, 2018 Under Topic 606 Under Topic 605 Effect of Change Net income $ (1,862 ) $ (26,661 ) $ 24,799 Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Deferred revenue - related party (4,652 ) 20,147 (24,799 )
Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash in Statement of Financial Position to Total Amount Reported in Statement of Cash Flows	The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the balance sheet that sum to the total of the same such amounts shown in the statement of cash flows. As of September 30, 2018 2017 Cash and cash equivalents $ 41,592 $ 31,320 Restricted cash included in current assets — 85 Restricted cash included in non-current assets 1,198 1,000 Total cash, cash equivalents, and restricted cash shown in the statement of cash flows $ 42,790 $ 32,405

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2018
Marketable Securities [Abstract]
Summary of Fair Value of Available-for-sale Marketable Debt Securities by Type of Security	As of September 30, 2018, the fair value of available-for-sale marketable debt securities by type of security was as follows: September 30, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable debt securities: U.S. Treasury notes $ 107,651 $ — $ (55 ) $ 107,596 U.S. Government agency bonds 2,900 — (23 ) 2,877 Corporate bonds 21,422 — (112 ) 21,310 $ 131,973 $ — $ (190 ) $ 131,783 As of December 31, 2017, the fair value of available-for-sale marketable debt securities by type of security was as follows: December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable debt securities: U.S. government agency bonds $ 7,300 $ — $ (38 ) $ 7,262 Corporate bonds 33,800 — (208 ) $ 33,592 $ 41,100 $ — $ (246 ) $ 40,854
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, 2018 Amortized Cost Fair Value Maturing in one year or less $ 131,973 $ 131,783 $ 131,973 $ 131,783 The amortized cost and fair value of the Company’s available-for-sale securities by contractual maturity are summarized as follows: December 31, 2017 Amortized Cost Fair Value Maturing in one year or less $ 27,769 $ 27,672 Maturing after one year but less than two years 13,331 13,182 $ 41,100 $ 40,854

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 30,856 $ — $ — $ 30,856 Marketable securities: U.S. Treasury notes — 107,596 — 107,596 U.S. Government agency bonds — 2,877 — 2,877 Corporate bonds — 21,310 — 21,310 $ 30,856 $ 131,783 $ — $ 162,639 Fair Value Measurements as of December 31, 2017 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 17,409 $ — $ — $ 17,409 Marketable securities: U.S. government agency bonds — 7,262 — 7,262 Corporate bonds — 33,592 — 33,592 $ 17,409 $ 40,854 $ — $ 58,263

Collaboration Agreement with _2

Collaboration Agreement with Novartis (Tables)	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Collaboration Revenue Related Party	For the three and nine months ended September 30, 2018 and 2017, the Company recognized the following totals of collaboration revenue – related party: Three months ended September 30, 2018 Nine months ended September 30, 2018 2018 2017 2018 2017 Collaboration revenue - related party $ 1,730 $ 2,480 $ 49,653 $ 10,347
Summary of Changes in Contract Assets and Liabilities	The following table presents changes in the Company’s contract assets and liabilities during the nine months ended September 30, 2018 (in thousands): December 31, 2017 Additions Deductions September 30, 2018 Contract Liabilities (1) Total deferred revenue - related party $ 82,105 $ 45,000 $ (63,388 ) $ 63,717 (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 and cumulative catch-up adjustment recognized upon adoption of ASC 606 on January 1, 2018.

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding as of December 31, 2017 3,106,891 $ 3.68 8.69 $ 14,361 Granted 1,723,048 11.28 Exercised (107,508 ) 1.70 Forfeited (213,390 ) 5.46 Outstanding as of September 30, 2018 4,509,041 $ 6.54 8.25 $ 18,775 Options exercisable at September 30, 2018 1,663,869 $ 3.91 7.08 $ 10,683
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 income (loss): Nine months ended September 30, 2018 2017 Research and development expenses $ 2,111 $ 1,434 General and administrative expenses 1,884 2,602 $ 3,995 $ 4,036

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018 Nine months ended September 30, 2018 2018 2017 2018 2017 Basic and diluted net loss per share attributable to common stockholders: Numerator: Net loss $ (17,222 ) $ (14,405 ) $ (1,862 ) $ (29,604 ) Accretion of redeemable convertible preferred stock to redemption value — (10 ) (11 ) (30 ) Net loss attributable to common stockholders $ (17,222 ) $ (14,415 ) $ (1,873 ) $ (29,634 ) Denominator: Weighted average commons shares outstanding—basic and diluted 27,598,251 2,506,150 17,398,249 2,446,156 Net loss per share attributable to common stockholders—basic and diluted $ (0.62 ) $ (5.75 ) $ (0.11 ) $ (12.11 )
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, 2018 2017 Redeemable convertible preferred shares (as converted to common stock) — 16,863,624 Stock options to purchase common stock 4,509,041 3,121,147 4,509,041 19,984,771

Nature of the Business - Additi

Nature of the Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Apr. 23, 2018USD ($)$ / sharesshares	Apr. 06, 2018	Sep. 30, 2018USD ($)shares	Dec. 31, 2017USD ($)shares
Class Of Stock [Line Items]
State of incorporation			State of Delaware
Convertible preferred stock converted into common stock			6,248,589	20,703,575
Accumulated deficit | $			$ 62,071	$ 73,945
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
Net proceeds from issuance of common stock | $	$ 97,209
Private Placement | Novartis Institutes for Biomedical Research, Inc.
Class Of Stock [Line Items]
Issuance of common stock (in shares)	766,666
Shares issued, price per share | $ / shares	$ 15
Net proceeds from issuance of common stock | $	$ 11,500
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 | Private Placement | Novartis Institutes for Biomedical Research, Inc.
Class Of Stock [Line Items]
Issuance of common stock (in shares)			766,666

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Summary of Impact of Cumulative Effect of Accounting Changes Upon Adoption of the Revenue ASUs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue - related party, current and net of current portions	$ 63,717		$ 63,717			$ 82,105
Accumulated deficit	(62,071)		(62,071)			(73,945)
Deferred revenue - related party	15,760		15,760			9,837
Deferred revenue - related party, non-current	47,957		47,957			$ 72,268
Collaboration revenue - related party	1,730	$ 2,480	49,653	$ 10,347
Income from operations	(18,030)	(14,272)	(3,570)	(29,355)
Net income (loss)	(17,222)	(14,405)	(1,862)	(29,604)
Comprehensive income	(17,179)	$ (14,362)	(1,806)	(29,428)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Deferred revenue - related party			(4,652)	19,654
ASU 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue - related party, current and net of current portions					$ 68,369
Accumulated deficit					(60,209)
Collaboration revenue - related party			49,653	$ 10,347
Effect of Change | ASU 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue - related party, current and net of current portions					(13,736)
Accumulated deficit	24,799		24,799		$ 13,736
Deferred revenue - related party	1,339		1,339
Deferred revenue - related party, non-current	(39,873)		(39,873)
Collaboration revenue - related party	(1,904)		24,799
Income from operations	(1,904)		24,799
Net income (loss)	(1,904)		24,799
Comprehensive income	(1,904)		24,799
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Deferred revenue - related party			(24,799)
Under Topic 605 | ASU 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit	(86,870)		(86,870)
Deferred revenue - related party	14,421		14,421
Deferred revenue - related party, non-current	87,830		87,830
Collaboration revenue - related party	3,634		24,854
Income from operations	(16,126)		(28,369)
Net income (loss)	(15,318)		(26,661)
Comprehensive income	$ (15,275)		(26,605)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Deferred revenue - related party			$ 20,147

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash in Statement of Financial Position to Total Amount Reported in Statement of Cash Flows (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 41,592	$ 22,455	$ 31,320
Restricted cash		85	85
Restricted cash	1,198	1,000	1,000
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	$ 42,790	$ 23,540	$ 32,405	$ 11,080

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, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 131,973	$ 41,100
Gross Unrealized Losses	(190)	(246)
Fair Value	131,783	40,854
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	21,422	33,800
Gross Unrealized Losses	(112)	(208)
Fair Value	21,310	33,592
U.S. Treasury Notes
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	107,651
Gross Unrealized Losses	(55)
Fair Value	107,596
U.S. Government Agency Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,900	7,300
Gross Unrealized Losses	(23)	(38)
Fair Value	$ 2,877	$ 7,262

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, 2018	Dec. 31, 2017
Available For Sale Securities [Abstract]
Maturing in one year or less, Amortized Cost	$ 131,973	$ 27,769
Maturing after one year but less than two years, Amortized Cost		13,331
Amortized Cost	131,973	41,100
Maturing in one year or less, Fair Value	131,783	27,672
Maturing after one year but less than two years, Fair Value		13,182
Fair Value	$ 131,783	$ 40,854

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
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, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	$ 162,639	$ 58,263
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	30,856	17,409
U.S. Treasury Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	107,596
U.S. Government Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	2,877	7,262
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	21,310	33,592
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	30,856	17,409
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	30,856	17,409
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	131,783	40,854
Level 2 | U.S. Treasury Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	107,596
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	2,877	7,262
Level 2 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured on recurring basis	$ 21,310	$ 33,592

Fair Value of Financial Asset_2

Fair Value of Financial Assets - Additional Information (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017
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 ($)	1 Months Ended		3 Months Ended	9 Months Ended
	Feb. 28, 2018	Jan. 31, 2016	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued for investment received			0	0			0
Equity investment received from related party				$ 11,500,000
Deferred revenue - related party, current and net of current portions			$ 63,717,000	63,717,000			$ 82,105,000
Deferred revenue - Additions				45,000,000
Deferred revenue - related party, non-current			47,957,000	47,957,000			72,268,000
Performance obligations satisfied in previous period			1,181,000	19,908,000
ASU 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, current and net of current portions						$ 68,369,000
Novartis
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment for reimbursement of manufacturing costs incurred				3,437,000	$ 0
Novartis Collaboration
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum aggregate amount of potential option purchase, option exercise and milestone payments to be received								$ 5,000,000
Revenue performance obligation			63,717,000	63,717,000
Novartis Collaboration | Novartis
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum aggregate amount of potential option purchase, option exercise and milestone payments to be received								$ 5,000,000
Proceeds from collaboration arrangement				5,000,000
Deferred revenue - related party, current and net of current portions							$ 5,000,000
Novartis Collaboration | Novartis | ASU 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum aggregate amount of potential option purchase, option exercise and milestone payments to be received			5,000,000	5,000,000
Deferred revenue - Additions	$ 45,000,000
Revenue recognized under milestone payment				24,746,000
Deferred revenue - related party, non-current			$ 20,254,000	20,254,000
Novartis Collaboration | Novartis | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Receivables from from collaboration arrangement, counterparty		$ 67,500,000
Novartis Collaboration | Novartis | Up Front Payment Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from collaboration arrangement		$ 70,000,000
Novartis Collaboration | Novartis | Milestone Payment
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from collaboration arrangement				80,000,000
Novartis Collaboration | Novartis | Milestone Payment | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from collaboration arrangement				$ 1,167,500,000
Novartis Collaboration | Series A One Redeemable Convertible Preferred Stock | Novartis
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued for investment received		2,000,000
Novartis Collaboration | Private Placement | Novartis Institutes for Biomedical Research, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued for investment received		766,666
Share price		$ 15
Equity investment received from related party		$ 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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party	$ 1,730	$ 2,480	$ 49,653	$ 10,347
ASU 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party			$ 49,653	$ 10,347

Collaboration Agreement with _5

Collaboration Agreement with Novartis - Summary of Changes in Contract Assets and Liabilities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Change In Contract With Customer Asset And Liability [Abstract]
Deferred revenue - Beginning balance	$ 82,105
Deferred revenue - Additions	45,000
Deferred revenue - Deductions	(63,388)
Deferred revenue - Ending balance	$ 63,717

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock - Additional Information (Details) - shares	Sep. 30, 2018	Apr. 23, 2018	Dec. 31, 2017
Temporary Equity [Line Items]
Convertible preferred stock converted into common stock	6,248,589		20,703,575
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)	Apr. 23, 2018USD ($)$ / sharesshares	Sep. 30, 2018USD ($)Vote$ / sharesshares	Dec. 31, 2017$ / sharesshares
Subsidiary Sale Of Stock [Line Items]
Common stock, authorized		150,000,000	53,000,000
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
Convertible preferred stock converted into common stock		6,248,589	20,703,575
Common stock reserved for exercise of outstanding stock options		6,248,589	20,703,575
Shares of common stock available for future grant under 2014 Stock Incentive Plan		6,248,589	20,703,575
Initial Public Offering
Subsidiary Sale 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
Private Placement | Novartis Institutes for Biomedical Research, Inc.
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock (in shares)	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, 2018	Dec. 31, 2017	Mar. 09, 2018	Mar. 02, 2018	Feb. 12, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock shares available for further issuance		6,248,589	20,703,575
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost		$ 15,174
Unrecognized stock-based compensation cost, weighted-average period		3 years 25 days
Employee Stock Option | Non-Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding stock option held for purchase of shares of common stock		493,964	369,645
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
Number of shares of common stock authorized			4,489,839	5,203,730	5,089,839	4,498,930
Number of common stock shares available for further issuance			733,060
Weighted average grant-date fair value per share of stock options granted		$ 7.48	$ 3.72
2018 Stock Option and Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock authorized	1,545,454
Percentage of authorized number of shares of common stock outstanding	4.00%
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		1,482,730
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 authorized	256,818
Percentage of authorized number of shares of common stock outstanding	1.00%
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) - 2014 Plan - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Outstanding beginning balance	3,106,891
Number of Shares, Granted	1,723,048
Number of Shares, Exercised	(107,508)
Number of Shares, Forfeited	(213,390)
Number of Shares, Outstanding ending balance	4,509,041	3,106,891
Number of Shares, Options exercisable at September 30, 2018	1,663,869
Weighted Average Exercise Price, Outstanding beginning balance	$ 3.68
Weighted Average Exercise Price, Granted	11.28
Weighted Average Exercise Price, Exercised	1.70
Weighted Average Exercise Price, Forfeited	5.46
Weighted Average Exercise Price, Outstanding ending balance	6.54	$ 3.68
Weighted Average Exercise Price, Options exercisable at September 30, 2018	$ 3.91
Weighted Average Remaining Contractual Term (in years), Outstanding	8 years 3 months	8 years 8 months 8 days
Weighted Average Remaining Contractual Term (in years), Options exercisable	7 years 29 days
Aggregate Intrinsic Value	$ 18,775	$ 14,361
Aggregate Intrinsic Value, Options exercisable at September 30, 2018	$ 10,683

Stock-Based Awards - Summary _2

Stock-Based Awards - Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Stock Awards (Details) - 2018 Employee Stock Purchase Plan - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 3,995	$ 4,036
Research and Development Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	2,111	1,434
General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 1,884	$ 2,602

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net loss	$ (17,222)	$ (14,405)	$ (1,862)	$ (29,604)
Accretion of redeemable convertible preferred stock to redemption value		(10)	(11)	(30)
Net loss attributable to common stockholders	$ (17,222)	$ (14,415)	$ (1,873)	$ (29,634)
Denominator:
Weighted average commons shares outstanding—basic and diluted	27,598,251	2,506,150	17,398,249	2,446,156
Net loss per share attributable to common stockholders—basic and diluted	$ (0.62)	$ (5.75)	$ (0.11)	$ (12.11)

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, 2018	Sep. 30, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	4,509,041	19,984,771
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	4,509,041	3,121,147
Redeemable Convertible Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share		16,863,624

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax provision or benefit	$ 0	$ 341,000	$ 0	$ 719,000
Prepaid income taxes	$ 923,000		$ 923,000		$ 6,657,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - Lease Amendment $ in Thousands	1 Months Ended
	May 30, 2018USD ($)ft²
Long Term Purchase Commitment [Line Items]
Lease term, description	In May 2018, the Company executed an amendment to lease an additional 33,529 square feet for a term of 10 years at 50 Hampshire Street that is intended to support its continued growth. The original lease term was extended to co-terminate with the additional space. The Company will pay annual rent of $71.00 per rentable square foot for the first year, with increases of $1.00 per rentable square foot for the remainder of the term. The additional space will be available for occupancy in 2020.
Land subject to additional ground leases | ft²	33,529
Annual rent	$ 71
Increase in annual rent	$ 1
Lease term	10 years

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - Vaccinex, Inc. - Technology Access Fee - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Expense incurred to related party	$ 66,000	$ 199,000
Due to related party			$ 0