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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	May 01, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Trading Symbol	MCRB
Entity Registrant Name	Seres Therapeutics, Inc.
Entity Central Index Key	0001609809
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity File Number	001-37465
Entity Tax Identification Number	27-4326290
Entity Address, Address Line One	200 Sidney Street - 4th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	945-9626
Entity Common Stock Shares Outstanding		72,599,103
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.001
Security Exchange Name	NASDAQ

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 54,857	$ 65,126
Investments	20,237	29,690
Prepaid expenses and other current assets	3,385	3,588
Accounts receivable	2,084	1,785
Total current assets	80,563	100,189
Property and equipment, net	17,836	19,495
Operating lease assets	10,820	11,356
Restricted investments	1,400	1,400
Total assets	110,619	132,440
Current liabilities:
Accounts payable	5,521	4,859
Accrued expenses and other current liabilities	9,141	10,884
Operating lease liabilities	4,623	4,456
Deferred revenue - related party	19,974	20,960
Deferred revenue	4,855	4,834
Total current liabilities	44,114	45,993
Note payable, net of discount	24,754	24,648
Operating lease liabilities, net of current portion	14,444	15,676
Deferred revenue, net of current portion - related party	84,635	89,111
Deferred revenue, net of current portion	3,641	4,834
Other long-term liabilities	680	502
Total liabilities	172,268	180,764
Commitments and contingencies (Note 11)
Stockholders’ deficit:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at March 31, 2020 and December 31, 2019; no shares issued and outstanding at March 31, 2020 and December 31, 2019.
Common stock, $0.001 par value; 200,000,000 shares authorized at March 31, 2020 and December 31, 2019; 71,671,067 and 70,143,252 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	72	70
Additional paid-in capital	417,819	411,255
Accumulated other comprehensive income (loss)	(10)
Accumulated deficit	(479,530)	(459,649)
Total stockholders’ deficit	(61,649)	(48,324)
Total liabilities and stockholders’ deficit	$ 110,619	$ 132,440

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	71,671,067	70,143,252
Common stock, shares outstanding	71,671,067	70,143,252

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue:
Collaboration revenue - related party	$ 5,462,000	$ 6,615,000
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Grant revenue	$ 739,000	$ 446,000
Collaboration revenue	1,988,000	260,000
Total revenue	8,189,000	7,321,000
Operating expenses:
Research and development expenses	21,743,000	22,887,000
General and administrative expenses	6,138,000	7,495,000
Restructuring expenses	0	1,492,000
Total operating expenses	27,881,000	31,874,000
Loss from operations	(19,692,000)	(24,553,000)
Other income (expense):
Interest income	159,000	220,000
Interest expense	(716,000)
Other income	368,000
Total other income (expense), net	(189,000)	220,000
Net loss	$ (19,881,000)	$ (24,333,000)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.28)	$ (0.59)
Weighted average common shares outstanding, basic and diluted	70,821,514	41,027,824
Net loss	$ (19,881,000)	$ (24,333,000)
Other comprehensive loss:
Unrealized loss on investments, net of tax of $0	(10,000)
Total other comprehensive loss	(10,000)
Comprehensive loss	$ (19,891,000)	$ (24,333,000)

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Unrealized gain on investment, tax	$ 0	$ 0

Condensed Consolidated Statement of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance at Dec. 31, 2018	$ (48,045)	$ 41	$ 341,284	$ (389,370)
Beginning balance, shares at Dec. 31, 2018		40,936,735
Issuance of common stock upon exercise of stock options, value	120		120
Issuance of common stock upon exercise of stock options, shares		38,125
Issuance of common stock upon vesting of RSUs, net of tax withholdings	153		153
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		73,500
Issuance of common stock under ESPP plan, value	207		207
Issuance of common stock under ESPP plan, shares		46,472
Stock-based compensation expense	2,065		2,065
Net loss	(24,333)			(24,333)
Ending balance at Mar. 31, 2019	(69,833)	$ 41	343,829	(413,703)
Ending balance, shares at Mar. 31, 2019		41,094,832
Beginning balance at Dec. 31, 2019	$ (48,324)	$ 70	411,255	(459,649)
Beginning balance, shares at Dec. 31, 2019	70,143,252	70,143,252
Issuance of common stock from at the market equity offering	$ 4,178	$ 1	4,177
Issuance of common stock from at the market equity offering, shares		1,230,531
Issuance of common stock upon exercise of stock options, value	$ 60	$ 1	59
Issuance of common stock upon exercise of stock options, shares	110,967	110,967
Issuance of common stock upon vesting of RSUs, net of tax withholdings	$ 120		120
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		110,000
Issuance of common stock under ESPP plan, value	249		249
Issuance of common stock under ESPP plan, shares		76,317
Stock-based compensation expense	1,959		1,959
Unrealized loss on investments	(10)				$ (10)
Net loss	(19,881)			(19,881)
Ending balance at Mar. 31, 2020	$ (61,649)	$ 72	$ 417,819	$ (479,530)	$ (10)
Ending balance, shares at Mar. 31, 2020	71,671,067	71,671,067

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (19,881)	$ (24,333)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	1,959	2,065
Depreciation and amortization expense	1,802	2,006
Non-cash operating lease cost	536	535
Accretion of discount on investments	(66)
Non-cash interest expense	314
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	203	(643)
Accounts receivable	(237)	(6,667)
Deferred revenue	(6,634)	(208)
Accounts payable	590	(2,474)
Operating lease liabilities	(1,066)	(1,024)
Accrued expenses and other current and long-term liabilities	(1,771)	(1,650)
Net cash (used in) operating activities	(24,251)	(32,393)
Cash flows from investing activities:
Purchases of property and equipment	(71)	(306)
Purchases of investments	(12,931)
Sales and maturities of investments	22,439
Net cash (used in) provided by investing activities	9,437	(306)
Cash flows from financing activities:
Proceeds from exercise of stock options	60	120
Proceeds from issuance of common stock and restricted common stock	120	153
Proceeds from at the market equity offering, net of commissions	4,116
Issuance of common stock under ESPP plan	249	207
Net cash provided by financing activities	4,545	480
Net increase (decrease) in cash and cash equivalents	(10,269)	(32,219)
Cash, cash equivalents and restricted cash at beginning of period	65,126	85,933
Cash, cash equivalents and restricted cash at end of period	54,857	53,714
Supplemental disclosure of cash flow information:
Cash paid for interest	610
Supplemental disclosure of non-cash investing and financing activities:
Unsettled issuance of common stock from the at the market offering	62
Property and equipment purchases included in accounts payable and accrued expenses	$ 133	$ 134

Nature of the Business and Basis of Presentation

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Nature of the Business and Basis of Presentation

1.	Nature of the Business and Basis of Presentation

Seres Therapeutics, Inc. (the “Company”) was incorporated under the laws of the State of Delaware in October 2010 under the name Newco LS21, Inc. In October 2011, the Company changed its name to Seres Health, Inc., and in May 2015, the Company changed its name to Seres Therapeutics, Inc. The Company is a microbiome therapeutics platform company developing a novel class of biological drugs, which are designed to treat disease by modulating the microbiome to restore heath by repairing the function of a dysbiotic microbiome to a non-disease state. The Company’s lead product candidate, SER-109, is designed to prevent further recurrences of Clostridioides difficile infection (formerly Clostridium difficile infection) (“CDI”), a debilitating infection of the colon, in patients who have received antibiotic therapy for recurrent CDI by treating the dysbiosis of the colonic microbiome. If approved by the U.S. Food and Drug Administration (“FDA”), SER-109 could be a first-in-field oral microbiome drug. SER-287 is being developed by the Company to treat ulcerative colitis (“UC”). In addition, using our microbiome therapeutics platform, the Company is also developing product candidates to treat diseases where the microbiome is implicated, including SER-301 and SER-155, both rationally designed, fermented therapeutics candidates for the treatment of UC, and to prevent mortality due to gastrointestinal infections, bacteremia and graft versus host disease (GvHD) in immunocompromised patients, including in patients receiving allogeneic hematopoietic stem cell transplantation (allo-HSCT) respectively, and SER-401, a microbiome therapeutic candidate for use with checkpoint inhibitors (“CPI’s”) in patients with metastatic melanoma. The Company continues to evaluate microbiome pharmacokinetic and pharmacodynamic data from their SER-262 Phase 1b study and other completed clinical trials, in addition to insights gained from research efforts with their other rationally designed Ecobiotic microbiome therapeutic candidates, in order to determine next steps in the development of SER-262 to treat an initial recurrence of CDI. The Company is also using its microbiome therapeutics platform to conduct research on various indications, including: metabolic diseases, inflammatory and immune diseases, and cancer.

The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive pre-clinical 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.

The Company’s product candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, or maintained, that any product candidates developed will obtain necessary government regulatory approval, or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants.

Under Accounting Standards Update (“ASU”) 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40) (“ASC 205-40”), the Company has the responsibility to evaluate whether conditions and/or events raise substantial doubt about its ability to meet its future financial obligations as they become due within one year after the date that the financial statements are issued. As required by ASC 205-40, this evaluation shall initially not take into consideration the potential mitigating effects of plans that have not been fully implemented as of the date the financial statements are issued.

As of March 31, 2020, the Company had an accumulated deficit of $479,530 and cash, cash equivalents and investments of $75,094. For the three months ended March 31, 2020, the Company incurred a loss of $19,881 and used $24,251 of cash in operations. Management has assessed the Company’s ability to continue as a going concern in accordance with the requirements of ASC 205-40 and determined that the Company’s accumulated deficit, history of losses, and future expected losses meet the ASC 205-40 standard for raising substantial doubt about the Company’s ability to continue as a going concern.

The Company’s current financial resources, proceeds received under the 2020 Sales Agreement subsequent to March 31, 2020 and currently forecasted operating plan would allow the Company to operate into the second quarter of 2021. The Company has developed plans to mitigate this risk, which primarily consist of raising additional capital through some combination of equity or debt financings, and/or potentially new collaborations and reducing cash expenditures. If the Company is not able to secure adequate additional funding, the Company plans to make reductions in spending. In that event, the Company may have to delay, scale back, or eliminate some or all of the Company’s planned clinical trials and research stage programs. The actions necessary to reduce spending under this plan at a level that mitigates the factors described above are not considered probable, as defined in the accounting standards and therefore, the full extent to which management may extend the Company’s funds through these actions may not be considered in management’s assessment of the Company’s ability to continue as a going concern. As a result, management has concluded that substantial doubt exists about the Company’s ability to continue as a going concern.

The Company is eligible to receive contingent milestone payments under its license and collaboration agreement with Nestec Ltd. (“NHS”), an affiliate of Nestlé Health Science US Holdings, Inc. (“Nestlé Health Science”), a significant stockholder of the Company, if certain development milestones are achieved. However, these milestones are uncertain and there is no assurance that the Company will receive any of them. Until such time, if ever, as the Company can generate substantial product revenue, the Company will finance its cash needs through a combination of public or private equity offerings, debt financings, governmental funding, collaborations, strategic partnerships, or marketing, distribution or licensing arrangements with third parties. The Company may not be able to obtain funding on acceptable terms, or at all. If the Company is unable to raise additional funds as and when needed, it would have a negative impact on the Company’s financial condition, which may require the Company to delay, reduce or eliminate certain research and development activities and reduce or eliminate discretionary operating expenses, which could constrain the Company’s ability to pursue its business strategies.

Unaudited Interim Financial Information

The accompanying unaudited condensed consolidated financial statements as of March 31, 2020 and for the three months ended March 31, 2020 have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2019 included in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2019, which was filed with the SEC on March 2, 2020 (the “Annual Report”).

The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the audited consolidated financial statements. The condensed consolidated balance sheet at December 31, 2019 was derived from audited annual financial statements, but does not contain all of the footnote disclosures from the annual financial statements. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position, results of operations, and cash flows for the periods presented. Such adjustments are of a normal and recurring nature. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

The significant accounting policies and estimates used in preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Annual Report. There have been no material changes to the Company’s significant accounting policies during the three months ended March 31, 2020.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition and the accrual of research and development expenses. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. The full extent to which the COVID-19 pandemic will directly or indirectly impact our business, results of operations and financial condition, including revenue, operating expenses, clinical trials and employee-related amounts, will depend on future developments that are highly uncertain, including new information that may emerge concerning COVID-19 and the actions taken to contain it or treat its impact and the economic impact on local, regional, national and international markets. We have made estimates of the impact of COVID-19 within our financial statements and there may be changes to those estimates in future periods. Actual results could differ from the Company’s estimates.

Net Loss per Share

Basic net loss per share is computed using the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed using the sum of the weighted average number of common shares outstanding during the period and, if dilutive, the weighted average number of potential shares of common stock, including the assumed exercise of stock options and unvested restricted stock.

The restricted stock units granted by the Company entitle the holder of such awards to ordinary cash dividends paid to substantially all holders of the Company’s common stock, as if such shares were outstanding common shares at the time of the dividend. The dividends are paid in cash or shares of common stock when the applicable restricted stock unit vests. However, the unvested restricted stock units are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

The following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:

	Three Months Ended March 31,
	2020		2019
Stock options to purchase common stock		10,755,593		8,908,432
Unvested restricted stock units		20,000		150,400
Shares issuable under ESPP		14,693		6,911
Total common stock equivalents		10,790,286		9,065,743

Recently Issued Accounting Standards

In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). This standard modifies certain disclosure requirements on fair value measurements. This standard became effective for the Company on January 1, 2020, and did not have a material impact on the Company’s disclosures.

In November 2018 the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606. This standard makes targeted improvements for collaborative arrangements as follows:

•

Clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606, Revenue from Contracts with Customers, when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in ASC 606 should be applied, including recognition, measurement, presentation and disclosure requirements;

•

Adds unit-of-account guidance to ASC 808, Collaborative Arrangements, to align with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606; and

•

Precludes a company from presenting transactions with collaborative participants that are not directly related to sales to third parties with revenue recognized under ASC 606 if the collaborative arrangement participant is not a customer.

This standard became effective for the Company on January 1, 2020 and did not have a material impact on the Company’s condensed consolidated financial statements and related disclosures.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (‘‘ASU 2016-13’’), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss model. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. These changes may result in earlier recognition of credit losses. In November 2018, the FASB issued ASU No. 2018-19, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, which narrowed the scope and changed the effective date for non-public entities for ASU 2016-13. The FASB subsequently issued supplemental guidance within ASU No. 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief (‘‘ASU 2019-05’’). ASU 2019-05 provides an option to irrevocably elect the fair value option for certain financial assets previously measured at amortized cost basis. For public entities that are Securities and Exchange Commission filers, excluding entities eligible to be smaller reporting companies, ASU 2016-13 is effective for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. For all other entities, ASU 2016-13 is effective for annual periods beginning after December 15, 2022, including interim periods within those fiscal years. Early adoption is permitted. This standard will be effective for the Company on January 1, 2023. The Company is currently evaluating the potential impact that this standard may have on its condensed consolidated financial statements and related disclosures.

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

3.Fair Value Measurements

The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis:

	Fair Value Measurements as of March 31, 2020 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	11,440	$	—	$	—	$	11,440
Commercial paper		—		5,992		—		5,992
Government securities		—		4,000		—		4,000
Investments:
Commercial paper	$	—	$	11,466	$	—	$	11,466
Corporate bonds		—		8,771		—		8,771
	$	11,440	$	30,229	$	—	$	41,669

	Fair Value Measurements as of December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	25,510	$	—	$	—	$	25,510
Commercial paper		—		4,243		—		4,243
Corporate bonds		—		4,900		—		4,900
Investments:
Commercial paper	$	—	$	11,957	$	—	$	11,957
Corporate bonds		—		17,733		—		17,733
	$	25,510	$	38,833	$	—	$	64,343

Money market funds were valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. Commercial paper and corporate bonds were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy. There were no transfers between Level 1 or Level 2 during the three months ended March 31, 2020.

As of March 31, 2020 and December 31, 2019 the Company held a restricted investment of $1,400, which represent a certificate of deposit that is classified as Level 2 in the fair value hierarchy.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Investments

3 Months Ended

Mar. 31, 2020

Investments Debt And Equity Securities [Abstract]

Investments

4.	Investments

Investments by security type consisted of the following at March 31, 2020 and December 31, 2019:

	March 31, 2020
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial paper	$	11,466	$	—	$	—		$	11,466
Corporate bonds		8,781		—		(10	)		8,771
	$	20,247	$	—	$	(10	)	$	20,237

	December 31, 2019
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial Paper	$	11,957	$	—	$	—		$	11,957
Corporate Bonds		17,732		3		(2	)		17,733
	$	29,689	$	3	$	(2	)	$	29,690

Investments with original maturities of less than 90 days are included in cash and cash equivalents on the condensed consolidated balance sheets and are not included in the table above. Investments with maturities of less than 12 months are considered current and those investments with maturities greater than 12 months are considered non-current assets.

Excluded from the table above in a restricted investment of $1,400 as the cost approximates current fair value.

Property and Equipment, Net

3 Months Ended

Mar. 31, 2020

Property Plant And Equipment [Abstract]

Property and Equipment, Net

5.	Property and Equipment, Net

Property and equipment, net consisted of the following:

	March 31, 2020			December 31, 2019
Laboratory equipment	$	15,381		$	15,140
Computer equipment		2,874			2,874
Furniture and office equipment		1,033			1,033
Leasehold improvements		27,977			27,977
Construction in progress		115			213
		47,380			47,237
Less: Accumulated depreciation and amortization	$	(29,544	)	$	(27,742	)
	$	17,836		$	19,495

Depreciation and amortization expense was $1,802 and $2,006 for the three months ended March 31, 2020 and 2019, respectively.

Accrued Expenses and Other Current Liabilities

3 Months Ended

Mar. 31, 2020

Payables And Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

6.	Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	March 31, 2020		December 31, 2019
Development and clinical manufacturing costs	$	5,974	$	5,605
Payroll and payroll-related costs		2,333		4,609
Facility and other		834		670
	$	9,141	$	10,884

Restructuring

3 Months Ended

Mar. 31, 2020

Restructuring And Related Activities [Abstract]

Restructuring

7.	Restructuring

In February 2019, the Company implemented corporate changes to focus its resources on advancing its clinical-stage therapeutic candidates. As a result, the Company is concentrating on obtaining results from the SER-109 Phase 3 study for recurrent CDI, completing the SER-287 Phase 2b study in mild-to-moderate UC, advancing the SER-401 Phase 1b study, in collaboration with the Parker Institute for Cancer Immunotherapy and MD Anderson Cancer Center, to evaluate augmenting checkpoint inhibitor response in patients with metastatic melanoma, and advancing SER-301 and SER-155 into clinical development. In connection with the prioritization of these therapeutic candidates, the Company made changes to its management team and reduced headcount by approximately 30 percent.

No restructuring charges were recorded during the three months ended March 31, 2020. During the three months ended March 31, 2019 the Company recorded charges of $1,492, related to severance and other termination benefits. During the three months ended March 31, 2020 and 2019 the Company paid $192 and $608, respectively. There are no remaining unpaid liabilities related to restructuring charges as of March 31, 2020.

Note Payable

3 Months Ended

Mar. 31, 2020

Debt Disclosure [Abstract]

Note Payable

8.	Note Payable

On October 29, 2019 (the “Closing Date”), the Company entered into a Loan and Security Agreement (the “Loan Agreement”) with Hercules Capital, Inc. (“Hercules”) pursuant to which a term loan in an aggregate principal amount of up to $50,000 (the “Term Loan Facility”) is available to the Company in three tranches, subject to certain terms and conditions. The first tranche of $25,000 was advanced to the Company on the Closing Date. Upon satisfaction of certain milestones, the second tranche is available under the Term Loan Facility which allows the Company to borrow an additional amount up to $12,500 through March 15, 2021. The third tranche, which allows the Company to borrow an additional $12,500, will be available upon Hercules’ approval on or prior to June 30, 2021.

Advances under the Term Loan Facility will bear interest at a rate equal to the greater of either (i) the Prime Rate (as reported in The Wall Street Journal) plus 4.40%, and (ii) 9.65%. The Company will make interest only payments through December 1, 2021. The interest only period may be extended to June 1, 2022 upon satisfaction of certain milestones. Following the interest only period, the Company will repay the principal balance and interest of the advances in equal monthly installments through November 1, 2023.

The Company may prepay advances under the Loan Agreement, in whole or in part, at any time subject to a prepayment charge (the “Prepayment Premium”) equal to: (a) 3.0 % of amounts so prepaid, if such prepayment occurs during the first year following the Closing Date; (b) 2.0% of the amount so prepaid, if such prepayment occurs during the second year following the Closing Date, and (c) 1.0% of the amount so prepaid, if such prepayment occurs after the second year following the Closing Date.

Upon prepayment or repayment of all or any of the term loans under the Term Loan Facility, the Company will pay (in addition to any Prepayment Premium) an end of term charge of 4.85% of the aggregate funded amount under the Term Loan Facility. With respect to the first tranche, an end of term charge of $1,213 will be payable upon any prepayment or repayment. To the extent that the Company is provided additional advances under the Term Loan Facility, the 4.85% end of term charge will be applied to any such additional amounts.

The Term Loan Facility is secured by substantially all of the Company’s assets, other than the Company’s intellectual property. The Company has agreed to not pledge or secure its intellectual property to others.

Upon issuance, the first tranche was recorded as a liability with an initial carrying value of $24,575, net of debt issuance costs. The initial carrying value will be accreted to the repayment amount, which includes the outstanding principal plus the end of term charge, through interest expense using the effective interest rate method over the term of the debt. The carrying value of the debt, which is classified as a non-current liability on the Company’s consolidated balance sheet, is $24,754 and $24,648 as of March 31, 2020 and December 31, 2019, respectively.

As of March 31, 2020 the future principal payments due under the arrangement, excluding interest and the end of term charge, are as follows:

Year Ending December 31,	Principal
2020 (remaining 9 months)	$	—
2021		949
2022		11,970
2023		12,081
Total	$	25,000

During the three months ended March 31, 2020, the Company recognized $716 of interest expense related to the Loan Agreement, which is reflected in interest expense on the condensed consolidated statement of operations and comprehensive loss.

Common Stock and Stock-Based Awards

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Common Stock and Stock-Based Awards

9.	Common Stock and Stock-Based Awards

Common Stock

In November 2019, the Company entered into a sales agreement, the 2019 Sales Agreement, with Cowen and Company, LLC (“Cowen”) to sell shares of its common stock with aggregate gross sales proceeds of up to $25,000, from time to time, through an ATM under which Cowen acts as sales agent. On March 18, 2020, in connection with filing an updated Registration Statement on Form S-3 (File No. 333-237033), the Company entered into a new sales agreement, the 2020 Sales Agreement, with Cowen on substantially the same terms as the 2019 Sales Agreement and terminated the 2019 Sales Agreement. From January 1, 2020 to March 31, 2020 the Company sold approximately 1,230,531 shares of common stock under the 2019 Sales Agreement and the 2020 Sales Agreement, as applicable, at an average price of approximately $3.50 per share, raising aggregate net proceeds of approximately $4,178 after deducting an aggregate commission of approximately 3%.

Stock Options

The following table summarizes the Company’s stock option activity since December 31, 2019:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2019		8,310,683		$	10.36		7.01	$	3,427
Granted		2,957,750			3.30
Exercised		(110,967	)		0.48
Forfeited		(401,873	)		8.62
Outstanding as of March 31, 2020		10,755,593		$	8.58		7.38	$	4,055
Options vested and expected to vest as of March 31, 2020		10,755,593		$	8.58		7.38	$	4,055
Options exercisable as of March 31, 2020		5,080,248		$	12.41		5.38	$	3,110

The weighted average grant-date fair value of stock options granted during the three months ended March 31, 2020 and 2019 was $2.06 and $4.60 per share, respectively.

During the three months ended March 31, 2019, the Company granted performance-based stock options to employees for the purchase of an aggregate of 1.1 million shares of common stock with a grant date fair value of $4.58 per share. These stock options are exercisable only upon achievement of specified performance targets. As of March 31, 2020, none of these options were exercisable because none of the specified performance targets had been achieved. Because achievement of the specified performance targets was not deemed probable as of March 31, 2020, the Company did not record any expense for these stock options from the dates of issuance through March 31, 2020.

Restricted Stock Units

The Company has granted restricted stock units with time-based vesting conditions. The table below summarizes the Company’s restricted stock unit activity since December 31, 2019:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2019		130,000		$	8.86
Granted		—			—
Forfeited		—			—
Vested		(110,000	)		9.98
Unvested restricted stock units as of March 31, 2020		20,000		$	2.69

Stock-based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss:

	Three Months Ended March 31,
	2020		2019
Research and development expenses	$	1,004	$	1,448
General and administrative expenses		955		617
	$	1,959	$	2,065

Collaboration Revenue

3 Months Ended

Mar. 31, 2020

Revenue From Contract With Customer [Abstract]

Collaboration Revenue

10.	Collaboration Revenue

NHS Collaboration Agreement

Summary of Agreement

In January 2016, the Company entered into a collaboration and license agreement with NHS (“License Agreement”) for the development and commercialization of certain product candidates for the treatment and management of CDI and IBD, including UC and Crohn’s disease. The License Agreement supports the development of the Company’s portfolio of products for CDI and IBD in markets outside of the United States and Canada (the “Licensed Territory”). The Company has retained full commercial rights to its entire portfolio of product candidates with respect to the United States and Canada.

Under the License Agreement, the Company granted to NHS an exclusive, royalty-bearing license to develop and commercialize, in the Licensed Territory, certain products based on its microbiome technology that are being developed for the treatment of CDI and IBD, including SER-109, SER-262, SER-287 and SER-301 (collectively, the “NHS Collaboration Products”). The License Agreement sets forth the Company’s and NHS’ respective obligations for development, commercialization, regulatory and manufacturing and supply activities for the NHS Collaboration Products with respect to the licensed fields and the Licensed Territory.

Under the License Agreement, NHS agreed to pay the Company an upfront cash payment of $120,000, which the Company received in February 2016. The Company is eligible to receive up to $285,000 in development milestone payments, $375,000 in regulatory payments and up to an aggregate of $1,125,000 for the achievement of certain commercial milestones related to the sales of NHS Collaboration Products. NHS also agreed to pay the Company tiered royalties, at percentages ranging from the high single digits to high teens, of net sales of NHS Collaboration Products in the Licensed Territory.

Under the License Agreement, the Company is entitled to receive a $20,000 milestone payment from NHS following initiation of a SER-287 Phase 2 study and a $20,000 milestone payment from NHS following the initiation of a SER-287 Phase 3 study. In November 2018, the Company entered into a letter agreement with NHS which modified the License Agreement to address the current clinical plans for SER-287. Pursuant to the letter agreement, the Company and NHS agreed that following initiation of the SER-287 Phase 2b study, the Company would be entitled to receive $40,000 in milestone payments from NHS, which represent the milestone payments due to the Company for the initiation of a SER-287 Phase 2 study and a Phase 3 study. The SER-287 Phase 2b study was initiated and the $40,000 of milestone payments were received in December 2018. The letter agreement also provides scenarios under which NHS’ reimbursement to the Company for certain Phase 3 development costs would be reduced or delayed depending on the outcomes of the SER-287 Phase 2b study.

Accounting Analysis

The Company assessed the License Agreement in accordance with ASC 606—Revenue From Contracts with Customers (“ASC 606”) and concluded that NHS is a customer. The Company identified the following promises under the contract: (i) a license to develop and commercialize the NHS Collaboration Products in the Licensed Territory, (ii) obligation to perform research and development services, (iii) participation on a joint steering committee, and (iv) manufacturing services to provide clinical supply to complete future clinical trials. In addition, the Company identified a contingent obligation to perform manufacturing services to provide commercial supply if commercialization occurs, which is contingent upon regulatory approval. This contingent obligation is not a performance obligation at inception and has been excluded from the initial allocation as it represents a separate buying decision at market rates, rather than a material right in the contract. The Company assessed the promised goods and services to determine if they are distinct. Based on this assessment, the Company determined that NHS cannot benefit from the promised goods and services separately from the others as they are highly interrelated and therefore not distinct. Accordingly, the promised goods and services represent one combined performance obligation and the entire transaction price will be allocated to that single combined performance obligation.

At contract inception, the Company determined that the $120,000 non-refundable upfront amount constituted the entirety of the consideration to be included in the transaction price as the development, regulatory, and commercial milestones were fully constrained. During the year ended December 31, 2016, the Company received $10,000 from NHS in connection with the initiation of the Phase 1b study for SER-262 in CDI. During the year ended December 31, 2017, the Company received $20,000 from NHS in connection with the initiation of the Phase 3 study for SER-109. During the year ended December 31, 2018, the Company received $40,000 from NHS in connection with the initiation of the Phase 2b study for SER-287. The transaction price as of March 31, 2020 was approximately $190,000.

During the three months ended March 31, 2020 and 2019, using the cost-to-cost method, which best depicts the transfer of control to the customer, the Company recognized $5,462 and $6,615 of Collaboration revenue – related party, respectively.

As of March 31, 2020 and December 31, 2019, there was $104,609, and $110,071, respectively, of deferred revenue related to the unsatisfied portion of the performance obligation under the License Agreement. As of March 31, 2020, the deferred revenue is classified as current or non-current in the condensed consolidated balance sheets based on the Company’s estimate of revenue that will be recognized within the next 12 months, which is determined by the cost-to-cost method which measures the extent of progress towards completion based on the ratio of actual costs incurred to the total estimated costs expected upon satisfying the performance obligation. All costs associated with the License Agreement are recorded in research and development expense in the condensed consolidated statements of operations and comprehensive loss.

AstraZeneca Research Collaboration and Option Agreement

Summary of the Agreement

In March 2019, the Company entered into a Research Collaboration and Option Agreement (the “Research Agreement”) with MedImmune, LLC, a wholly owned subsidiary of AstraZeneca Inc. (“AstraZeneca”), to advance the mechanistic understanding of the microbiome in augmenting the efficacy of cancer immunotherapy. Under the Research Agreement, the Company and AstraZeneca will conduct certain research and development activities as set forth on a research plan focused on the role of the microbiome in certain cancers and cancer immunotherapies, including furthering the research program for SER-401, in combination with AstraZeneca compounds targeting various cancers.

Pursuant to the Research Agreement, the Company agreed not to conduct research or development on any microbiome products specifically designed by the Company during the term of the Research Agreement for the treatment of cancer (“Microbiome Oncology Products”), with or on behalf of any third party without the prior approval of the joint steering committee for the Research Agreement for at least three years after the effective date (the “Exclusivity Period”). Additionally, AstraZeneca will pay to the Company a total of $20,000 in three equal installments, the first of which the Company received in April 2019, the second of which the Company received in December 2019, and the third of which becomes due on January 4, 2021. Such payments are payable even if the Research Agreement is terminated in accordance with its terms, unless the Research Agreement is terminated by AstraZeneca for the Company’s uncured material breach. Additionally, AstraZeneca will bear its costs of conducting activities under the research plan and will reimburse the Company for all activities performed under the research plan based on actual full-time employee (“FTE”) time and certain third-party costs incurred by the Company in connection therewith.

Under the Research Agreement, the Company granted to AstraZeneca an exclusive option to negotiate a worldwide, sublicensable exclusive license under relevant intellectual property rights controlled by the Company to exploit Microbiome Oncology Products for the treatment of cancer. Additionally, the Company granted to AstraZeneca an additional exclusive option to obtain a worldwide, sublicensable, license under certain intellectual property rights arising out of the Agreement or coming into the control of the Company during the term of the Agreement, to exploit AstraZeneca’s oncology and other assets which are the subject of the research plan. AstraZeneca may exercise each option at any point prior to 90 days after the end of the Exclusivity Period (the “Option Exercise Period”) by delivering an option exercise notice to the Company. If AstraZeneca exercises an option during the Option Exercise Period, the parties will enter into exclusive, good faith negotiations for a period of six months (the “Negotiation Period”) regarding the terms of the definitive license agreement contemplated by such option. If no definitive agreement is reached during the Negotiation Period, subject to certain other terms and conditions applicable for a one (1) year period, the Company is free to license, further develop or otherwise exploit its assets that were the subject of the option without further obligation to AstraZeneca.

The term of the Research Agreement continues in effect until the Research Agreement is terminated by the parties in accordance with its terms by mutual written agreement. Either party may terminate the Research Agreement for the other party’s uncured material breach or bankruptcy or insolvency-related events. AstraZeneca may terminate the Research Agreement for convenience.

Accounting Analysis

The Company assessed the Research Agreement in accordance with ASC 606 and concluded that AstraZeneca is a customer. The Company identified the following promises under the contract: (i) a research license, (ii) an obligation to perform research and development services, and (iii) participating on a joint steering committee. The Company assessed the promised goods and services to determine if they are distinct. Based on this assessment, the Company determined that AstraZeneca cannot benefit from the promised goods and services separately from the others as they are highly interrelated and therefore not distinct. Accordingly, the promised goods and services represent one combined performance obligation and the entire transaction price will be allocated to that single combined performance obligation.

Each exclusive option granted to AstraZeneca provides AstraZeneca with the right to negotiate a license agreement in the future at fair value. Therefore, the Company concluded that each option does not constitute a performance obligation at inception and has been excluded from the initial allocation since each option represents a separate buying decision at market rates, rather than a material right in the contract.

At contract inception, the Company determined that the transaction price is comprised of: (i) the $20,000 fee, which represents fixed consideration, and (ii) the estimated reimbursement of research and development costs incurred, which represents variable consideration. The Company included the estimated reimbursement of research and development costs, approximately $13,900, in the transaction price at the inception of the arrangement because the Company is required to perform research and development services and the contract requires AstraZeneca to reimburse the Company for costs incurred. Also, since the related revenue would be recognized only as the costs are incurred, and the contract precludes the joint steering committee from changing the research plan without mutual agreement, the Company determined it is not probable that a significant reversal of cumulative revenue would occur.

The Company determined that revenue under the Research Agreement should be recognized over time as AstraZeneca simultaneously receives the benefit from the Company as the Company performs under the single performance obligation over time. The Company will recognize revenue for the single performance obligation using a cost-to-cost input method as the Company has concluded it best depicts the research and joint steering committee participation services performed prior to AstraZeneca’s ability to negotiate a license. Under this method, the transaction price is recognized over the contract’s entire performance period, using costs incurred relative to total estimated costs to determine the extent of progress towards completion.

For the three months ended March 31, 2020 and 2019 the Company recognized collaboration revenue of $1,988 and $260, respectively, based on the measured progress under the Research Agreement. The transaction price as of March 31, 2020 was approximately $33,900.

As of March 31, 2020, there was $8,496 of deferred revenue associated with the Research Agreement, with $4,855 presented as current and $3,641 as non-current in the condensed consolidated balance sheets based on the Company’s estimate of revenue that will be recognized within the next 12 months. All costs associated with the Research Agreement are recorded in research and development expense in the condensed consolidated statements of operations and comprehensive loss.

Contract Balances from Contracts with Customers

The following table presents changes in the Company’s contract liabilities during the three months ended March 31, 2020 and 2019:

	Balance as of December 31, 2019		Additions		Deductions			Balance as of March 31, 2020
Three months ended March 31, 2020
Contract liabilities:
Deferred revenue - related party		110,071		—		(5,462	)		104,609
Deferred revenue		9,668		816		(1,988	)		8,496

	Balance as of December 31, 2018		Additions		Deductions			Balance as of March 31, 2019
Three months ended March 31, 2019
Contract liabilities:
Deferred revenue - related party		137,259		—		(6,615	)		130,644
Deferred revenue		—		6,667		(260	)		6,407

During the three months ended March 31, 2020 and 2019 the Company recognized the following revenues as a result of changes in the contract liabilities balances in the respective periods (in thousands):

	Three Months Ended March 31,
	2020		2019
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period		6,634		6,615

When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded. Revenue is recognized from the contract liability over time using the cost-to-cost method.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

11.	Commitments and Contingencies

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its condensed consolidated financial statements as of March 31, 2020 or December 31, 2019.

Legal Contingencies

The Company accrues a liability for legal contingencies when it believes that it is both probable that a liability has been incurred and that the Company can reasonably estimate the amount of the loss. The Company reviews these accruals and adjusts them to reflect ongoing negotiations, settlements, rulings, advice of legal counsel and other relevant information. To the extent new information is obtained and the views on the probable outcomes of claims, suits, assessments, investigations or legal proceedings change, changes in the Company’s accrued liabilities would be recorded in the period in which such determination is made.

In addition, in accordance with the relevant authoritative guidance, for any matters in which the likelihood of material loss is at least reasonably possible, the Company will provide disclosure of the possible loss or range of loss. If a reasonable estimate cannot be made, however, the Company will provide disclosure to that effect. The Company expenses legal costs as they are incurred.

The Company did not accrue any liabilities related to legal contingencies in its condensed consolidated financial statements as of March 31, 2020 or December 31, 2019.

Income Taxes

3 Months Ended

Mar. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

12.	Income Taxes

The Company did not provide for any income taxes for the three months ended March 31, 2020.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of March 31, 2020 and December 31, 2019. Management reevaluates the positive and negative evidence at each reporting period.

As of March 31, 2020 and December 31, 2019, the Company had no accrued interest or tax penalties recorded. The Company files income tax returns in the United States and various state jurisdictions. The Company is no longer subject to U.S. federal income tax examinations by tax authorities for years before 2012. However, to the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service or state tax authorities to the extent it is utilized in a future period. There are no currently ongoing or pending examinations in any jurisdictions.

Related Party Transactions

3 Months Ended

Mar. 31, 2020

Related Party Transactions

13.	Related Party Transactions

As described in Note 10, in January 2016 the Company entered into the License Agreement with NHS for the development and commercialization of certain product candidates in development for the treatment and management of CDI and IBD, including UC and Crohn’s disease. NHS is a related party since NHS is an affiliate of Nestlé Health Science, one of the Company’s significant stockholders. During the three months ended March 31, 2020 and 2019, the Company recognized $5,462 and $6,615 of related party revenue associated with the License Agreement, respectively. As of March 31, 2020, there was $104,609 of deferred revenue related to the License Agreement, which is classified as current or non-current in the condensed consolidated balance sheets. The Company has made no payments to NHS during the three months ended March 31, 2020. There is no amount due from NHS as of March 31, 2020.

In July 2019, the Company entered into a sublease agreement with Flagship Pioneering, one of the Company’s significant stockholders, to sublease a portion of its office and laboratory space in Cambridge, Massachusetts. The term of the sublease agreement commenced in July 2019 and ends on the last day of the 24^th calendar month following commencement, with no option to extend. Under this agreement, the Company recorded other income of $450 during the three months ended March 31, 2020. The Company received cash payments of $450 during the three months ended March 31, 2020.

Subsequent Events

3 Months Ended

Mar. 31, 2020

Subsequent Events [Abstract]

Subsequent Events

14.	Subsequent Events

In April 2020, preclinical research activities contemplated under the original research plan, in connection with the Research Agreement, have been curtailed. The Company is currently in discussions with AstraZeneca regarding the future scope of translational and clinical activities to be performed under the research plan. While we discuss with AstraZeneca the scope of future activities to be performed under the research plan we expect revenue recognized under the Research Agreement to decrease.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Use of Estimates

Net Loss per Share

	Three Months Ended March 31,
	2020		2019
Stock options to purchase common stock		10,755,593		8,908,432
Unvested restricted stock units		20,000		150,400
Shares issuable under ESPP		14,693		6,911
Total common stock equivalents		10,790,286		9,065,743

Recently Issued Accounting Standards

•

This standard became effective for the Company on January 1, 2020 and did not have a material impact on the Company’s condensed consolidated financial statements and related disclosures.

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share

	Three Months Ended March 31,
	2020		2019
Stock options to purchase common stock		10,755,593		8,908,432
Unvested restricted stock units		20,000		150,400
Shares issuable under ESPP		14,693		6,911
Total common stock equivalents		10,790,286		9,065,743

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Summary of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis

The following tables present the Company’s fair value hierarchy for its assets and liabilities that are measured at fair value on a recurring basis:

	Fair Value Measurements as of March 31, 2020 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	11,440	$	—	$	—	$	11,440
Commercial paper		—		5,992		—		5,992
Government securities		—		4,000		—		4,000
Investments:
Commercial paper	$	—	$	11,466	$	—	$	11,466
Corporate bonds		—		8,771		—		8,771
	$	11,440	$	30,229	$	—	$	41,669

	Fair Value Measurements as of December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	25,510	$	—	$	—	$	25,510
Commercial paper		—		4,243		—		4,243
Corporate bonds		—		4,900		—		4,900
Investments:
Commercial paper	$	—	$	11,957	$	—	$	11,957
Corporate bonds		—		17,733		—		17,733
	$	25,510	$	38,833	$	—	$	64,343

Investments (Tables)

3 Months Ended

Mar. 31, 2020

Investments Debt And Equity Securities [Abstract]

Schedule of Investments by Security Type

Investments by security type consisted of the following at March 31, 2020 and December 31, 2019:

	March 31, 2020
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial paper	$	11,466	$	—	$	—		$	11,466
Corporate bonds		8,781		—		(10	)		8,771
	$	20,247	$	—	$	(10	)	$	20,237

	December 31, 2019
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial Paper	$	11,957	$	—	$	—		$	11,957
Corporate Bonds		17,732		3		(2	)		17,733
	$	29,689	$	3	$	(2	)	$	29,690

Property and Equipment, Net (Tables)

3 Months Ended

Mar. 31, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consisted of the following:

	March 31, 2020			December 31, 2019
Laboratory equipment	$	15,381		$	15,140
Computer equipment		2,874			2,874
Furniture and office equipment		1,033			1,033
Leasehold improvements		27,977			27,977
Construction in progress		115			213
		47,380			47,237
Less: Accumulated depreciation and amortization	$	(29,544	)	$	(27,742	)
	$	17,836		$	19,495

Accrued Expenses and Other Current Liabilities (Tables)

3 Months Ended

Mar. 31, 2020

Payables And Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	March 31, 2020		December 31, 2019
Development and clinical manufacturing costs	$	5,974	$	5,605
Payroll and payroll-related costs		2,333		4,609
Facility and other		834		670
	$	9,141	$	10,884

Note Payable (Tables)

3 Months Ended

Mar. 31, 2020

Debt Disclosure [Abstract]

Summary of Future Principal Payments Due Under Arrangement, Excluding Interest and End of Term Charge

As of March 31, 2020 the future principal payments due under the arrangement, excluding interest and the end of term charge, are as follows:

Year Ending December 31,	Principal
2020 (remaining 9 months)	$	—
2021		949
2022		11,970
2023		12,081
Total	$	25,000

Common Stock and Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since December 31, 2019:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2019		8,310,683		$	10.36		7.01	$	3,427
Granted		2,957,750			3.30
Exercised		(110,967	)		0.48
Forfeited		(401,873	)		8.62
Outstanding as of March 31, 2020		10,755,593		$	8.58		7.38	$	4,055
Options vested and expected to vest as of March 31, 2020		10,755,593		$	8.58		7.38	$	4,055
Options exercisable as of March 31, 2020		5,080,248		$	12.41		5.38	$	3,110

Summary of Restricted Stock Unit Activity

The Company has granted restricted stock units with time-based vesting conditions. The table below summarizes the Company’s restricted stock unit activity since December 31, 2019:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2019		130,000		$	8.86
Granted		—			—
Forfeited		—			—
Vested		(110,000	)		9.98
Unvested restricted stock units as of March 31, 2020		20,000		$	2.69

Summary of Stock Based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss:

	Three Months Ended March 31,
	2020		2019
Research and development expenses	$	1,004	$	1,448
General and administrative expenses		955		617
	$	1,959	$	2,065

Collaboration Revenue (Tables)

3 Months Ended

Mar. 31, 2020

Revenue From Contract With Customer [Abstract]

Changes in Contract Liabilities

The following table presents changes in the Company’s contract liabilities during the three months ended March 31, 2020 and 2019:

	Balance as of December 31, 2019		Additions		Deductions			Balance as of March 31, 2020
Three months ended March 31, 2020
Contract liabilities:
Deferred revenue - related party		110,071		—		(5,462	)		104,609
Deferred revenue		9,668		816		(1,988	)		8,496

	Balance as of December 31, 2018		Additions		Deductions			Balance as of March 31, 2019
Three months ended March 31, 2019
Contract liabilities:
Deferred revenue - related party		137,259		—		(6,615	)		130,644
Deferred revenue		—		6,667		(260	)		6,407

	Three Months Ended March 31,
	2020		2019
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period		6,634		6,615

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Entity incorporated year	Oct. 31, 2010
Entity incorporation, state or country code	DE
Accumulated deficit	$ 479,530		$ 459,649
Net loss	(19,881)	$ (24,333)
Cash used in operations	(24,251)	$ (32,393)
Cash, cash equivalents and investments	$ 75,094

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Summary of Significant Accounting Policies - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	10,790,286	9,065,743
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	10,755,593	8,908,432
Unvested Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	20,000	150,400
Shares Issuable under ESPP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	14,693	6,911

Fair Value Measurements - Summary of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investments:
Investments	$ 20,237	$ 29,690
Fair Value, Measurements, Recurring [Member]
Investments:
Investments	41,669	64,343
Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash equivalents	11,440	25,510
Commercial Paper [Member]
Investments:
Investments	11,466	11,957
Commercial Paper [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents	5,992	4,243
Investments:
Investments	11,466	11,957
Corporate Bonds [Member]
Investments:
Investments	8,771	17,733
Corporate Bonds [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents		4,900
Investments:
Investments	8,771	17,733
Government Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents	4,000
Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Investments:
Investments	11,440	25,510
Level 1 [Member] \| Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash equivalents	11,440	25,510
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Investments:
Investments	30,229	38,833
Level 2 [Member] \| Commercial Paper [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents	5,992	4,243
Investments:
Investments	11,466	11,957
Level 2 [Member] \| Corporate Bonds [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents		4,900
Investments:
Investments	8,771	$ 17,733
Level 2 [Member] \| Government Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Cash equivalents:
Cash equivalents	$ 4,000

Fair Value Measurements - Additional Information (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair value, assets transfers from Level 1 to Level 2 measurement	$ 0	$ 0
Fair value, assets transfers from Level 2 to Level 1 measurement	0	0
Restricted investments	$ 1,400,000	$ 1,400,000

Investments - Schedule of Investments by Security Type (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 20,247	$ 29,689
Gross Unrealized Gain		3
Gross Unrealized Loss	(10)	(2)
Fair Value	20,237	29,690
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,466	11,957
Fair Value	11,466	11,957
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,781	17,732
Gross Unrealized Gain		3
Gross Unrealized Loss	(10)	(2)
Fair Value	$ 8,771	$ 17,733

Investments - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Investments [Abstract]
Maximum maturity days for cash equivalents	90 days
Restricted investment	$ 1,400	$ 1,400

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 47,380	$ 47,237
Less: Accumulated depreciation and amortization	(29,544)	(27,742)
Property and equipment, net	17,836	19,495
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	15,381	15,140
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,874	2,874
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,033	1,033
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,977	27,977
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 115	$ 213

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 1,802	$ 2,006

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Development and clinical manufacturing costs	$ 5,974	$ 5,605
Payroll and payroll-related costs	2,333	4,609
Facility and other	834	670
Total accrued expenses and other current liabilities	$ 9,141	$ 10,884

Restructuring - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Feb. 28, 2019	Mar. 31, 2020	Mar. 31, 2019
Restructuring Cost And Reserve [Line Items]
Percent of reduction in headcount of employees	30.00%
Restructuring Charges		$ 0	$ 1,492,000
Cash payments		192,000	608,000
Remaining unpaid liabilities related to restructuring charges		$ 0
Severance And Other Termination Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring Charges			$ 1,492,000

Note Payable - Additional Information (Detail) - USD ($)		3 Months Ended
	Oct. 29, 2019	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Interest expense		$ 716,000
Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Interest expense		716,000
Loan and Security Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, interest rate	9.65%
Credit facility, payment terms	The Company will make interest only payments through December 1, 2021. The interest only period may be extended to June 1, 2022 upon satisfaction of certain milestones. Following the interest only period, the Company will repay the principal balance and interest of the advances in equal monthly installments through November 1, 2023.
Percentage of prepayment amount during first year	3.00%
Percentage of prepayment amount during second year	2.00%
Percentage of prepayment amount during third year	1.00%
Prepayment or repayment percentage	4.85%
Additional advance prepayment or repayment percentage	4.85%
Carrying value of debt		$ 24,754,000	$ 24,648,000
Loan and Security Agreement [Member] \| Term Loan Facility [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Debt instrument, variable rate	4.40%
Hercules Capital, Inc. [Member] \| Loan and Security Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	$ 50,000,000
First Tranche [Member] \| Loan and Security Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Prepayment or repayment charge	1,213,000
Carrying value of debt	24,575,000
First Tranche [Member] \| Hercules Capital, Inc. [Member] \| Loan and Security Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Gross proceeds from debt	25,000,000
Second Tranche Available Through March 15, 2021 [Member] \| Hercules Capital, Inc. [Member] \| Loan and Security Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	12,500,000
Third Tranche Available Upon Approval on or Prior to June 30, 2021 [Member] \| Hercules Capital, Inc. [Member] \| Loan and Security Agreement [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, aggregate principal amount	$ 12,500,000

Note Payable - Summary of Future Principal Payments Due Under Arrangement, Excluding Interest and End of Term Charge (Detail) $ in Thousands	Mar. 31, 2020 USD ($)
Debt Disclosure [Abstract]
2021	$ 949
2022	11,970
2023	12,081
Total	$ 25,000

Common Stock and Stock-Based Awards - Common Stock - Additional Information (Detail) - At The Market Equity Offering Program [Member] - Cowen And Company, LLC [Member] $ / shares in Units, $ in Thousands		3 Months Ended
	Nov. 27, 2019 USD ($)	Mar. 31, 2020 USD ($) $ / shares shares
2019 Sales Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Gross proceeds from sale of common stock	$ 25,000
2019 and 2020 Sales Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued \| shares		1,230,531
Common stock, average price per share \| $ / shares		$ 3.50
Net proceeds from sale of common stock		$ 4,178
Percentage of commission on sale of common stock		3

Common Stock and Stock-Based Awards - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Number of Shares, Beginning Balance	8,310,683
Number of Shares, Granted	2,957,750
Number of Shares, Exercised	(110,967)
Number of Shares, Forfeited	(401,873)
Number of Shares, Ending Balance	10,755,593	8,310,683
Number of Shares, Options vested and expected to vest	10,755,593
Number of Shares, Options exercisable	5,080,248
Weighted Average Exercise Price, Beginning Balance	$ 10.36
Weighted Average Exercise Price, Granted	3.30
Weighted Average Exercise Price, Exercised	0.48
Weighted Average Exercise Price, Forfeited	8.62
Weighted Average Exercise Price, Ending Balance	8.58	$ 10.36
Weighted Average Exercise Price, Options vested and expected to vest	8.58
Weighted Average Exercise Price, Options exercisable	$ 12.41
Weighted Average Remaining Contractual Term, Outstanding	7 years 4 months 17 days	7 years 3 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	7 years 4 months 17 days
Weighted Average Remaining Contractual Term, Options exercisable	5 years 4 months 17 days
Aggregate Intrinsic Value, Outstanding	$ 4,055	$ 3,427
Aggregate Intrinsic Value, Options vested and expected to vest	4,055
Aggregate Intrinsic Value, Options exercisable	$ 3,110

Common Stock and Stock-Based Awards - Stock Options - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options	$ 2.06	$ 4.60
Performance-based stock options to granted	2,957,750
Stock based compensation expense for stock options	$ 1,959,000	$ 2,065,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options	$ 4.58
Performance-based stock options to granted	1,100,000
Stock options exercisable	0
Stock based compensation expense for stock options	$ 0

Common Stock and Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member]	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested restricted stock units, Beginning balance \| shares	130,000
Number of Shares, Vested \| shares	(110,000)
Number of Shares, Unvested restricted stock units, Ending balance \| shares	20,000
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Beginning balance \| $ / shares	$ 8.86
Weighted Average Grant Date Fair Value, Vested \| $ / shares	9.98
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Ending balance \| $ / shares	$ 2.69

Common Stock and Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,959	$ 2,065
Research and development expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,004	1,448
General and administrative expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 955	$ 617

Collaboration Revenue - Additional Information (Detail)	1 Months Ended	3 Months Ended		12 Months Ended
Collaboration Revenue - Additional Information (Detail)	Mar. 31, 2019 USD ($) Installment	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)	Feb. 29, 2016 USD ($)	Jan. 31, 2016 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration/license fee		$ 120,000,000
Collaboration revenue - related party		5,462,000	$ 6,615,000
Collaboration revenue		1,988,000	260,000
Deferred revenue, current		4,855,000					$ 4,834,000
Deferred revenue, non-current		3,641,000					4,834,000
Research Agreement [Member] \| AstraZeneca Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment		8,496,000
Upfront collaboration milestone payments receivable	$ 20,000,000		20,000,000
Transaction price allocated to remaining performance obligations		$ 33,900,000
Minimum exclusivity period	3 years
Number of installments \| Installment	3
Option exercise period from exclusivity period		90 days
Terms of the definitive license agreement good faith negotiation period		6 months
Other terms of definitive license agreement period		1 year
Research and development fixed consideration		$ 20,000,000
Research and development estimated reimbursement costs		13,900,000
Collaboration revenue		1,988,000	260,000
Deferred revenue, current		4,855,000
Deferred revenue, non-current		3,641,000
Nestlé Health Science [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment		104,609,000							$ 120,000,000
Maximum development milestone payments to be received		285,000,000
Maximum regulatory payments to be received		375,000,000
Maximum amount to be received on achievement of certain commercial milestones		1,125,000,000
Proceeds on achievement of development milestone				$ 40,000,000	$ 20,000,000	$ 10,000,000
Transaction price allocated to remaining performance obligations		190,000,000
Collaboration revenue - related party		5,462,000	$ 6,615,000
Deferred revenue		$ 104,609,000					$ 110,071,000
Nestlé Health Science [Member] \| Phase 2 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable										$ 20,000,000
Nestlé Health Science [Member] \| Phase 3 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable										$ 20,000,000
Nestlé Health Science [Member] \| Phase 2b [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable								$ 40,000,000
Proceeds on achievement of development milestone				$ 40,000,000

Collaboration Revenue - Changes in Contract Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, Deductions	$ (6,634)	$ (6,615)
ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party, Balance at beginning of period	110,071	137,259
Deferred revenue - related party, Deductions	(5,462)	(6,615)
Deferred revenue - related party, Balance at end of period	104,609	130,644
Deferred revenue, Balance at beginning of period	9,668
Deferred revenue, Additions	816	6,667
Deferred revenue, Deductions	(1,988)	(260)
Deferred revenue, Balance at end of period	$ 8,496	$ 6,407

Collaboration Revenue - Schedule of Revenue Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$ 6,634	$ 6,615

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Indemnification Agreement [Member]
Other Commitments [Line Items]
Indemnification obligations accrued	$ 0	$ 0

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0
Accrued interest or tax penalties	$ 0	$ 0

Related Party Transactions - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Feb. 29, 2016
Related Party Transaction [Line Items]
Collaboration revenue - related party	$ 5,462,000	$ 6,615,000
Nestlé Health Science [Member]
Related Party Transaction [Line Items]
Collaboration revenue - related party	5,462,000	$ 6,615,000
Deferred revenue	104,609,000		$ 120,000,000
Payments under agreements with related party	0
Due from related party for the reimbursement of development costs	$ 0
Flagship Pioneering [Member] \| Sublease Agreement [Member]
Related Party Transaction [Line Items]
Sub lease commencement date	2019-07
Lessee, operating sublease, existence of option to extend	false
Lessee, operating sublease, option to extend, description	The term of the sublease agreement commenced in July 2019 and ends on the last day of the 24th calendar month following commencement, with no option to extend
Cash received from related party transaction	$ 450,000
Flagship Pioneering [Member] \| Sublease Agreement [Member] \| Other Income [Member]
Related Party Transaction [Line Items]
Sublease income	$ 450,000