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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	May 02, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	SYBX
Entity Registrant Name	SYNLOGIC, INC.
Entity Central Index Key	0001527599
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 Common Stock, Shares Outstanding		25,388,643

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 15,744	$ 11,252
Short-term marketable securities	94,091	111,477
Accounts receivable	2,500
Prepaid expenses and other current assets	1,457	1,609
Total current assets	113,792	124,338
Property and equipment, net	14,348	14,841
Right of use asset - operating lease	15,698
Restricted cash	1,097	1,097
Other assets	65	64
Total assets	145,000	140,340
Current liabilities:
Accounts payable	2,379	2,380
Accrued expenses	3,881	5,034
Deferred revenue	1,964	268
Deferred rent		393
Lease liability - operating lease	1,374
Finance lease obligations	269	266
Total current liabilities	9,867	8,341
Long-term liabilities:
Deferred rent, net of current portion		7,691
Deferred revenue, net of current portion	465
Lease liability - operating lease, net of current portion	22,317
Finance lease obligations, net of current portion	141	210
Total long-term liabilities	22,923	7,901
Commitments and contingencies (Note 11)
Stockholders' Equity
Preferred stock, $0.001 par value 5,000,000 shares authorized, none issued and outstanding as of March 31, 2019 and December 31, 2018
Common stock, $0.001 par value 250,000,000 shares authorized as of March 31, 2019 and December 31, 2018. 25,388,643 and 25,401,479 shares issued and outstanding as of March 31, 2019 and December 31, 2018, respectively.	25	25
Additional paid-in capital	244,857	243,903
Accumulated other comprehensive loss	39	(65)
Accumulated deficit	(132,711)	(119,765)
Total stockholders' equity	112,210	124,098
Total liabilities and stockholders' equity	$ 145,000	$ 140,340

Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, Shares Authorized	5,000,000	5,000,000
Preferred stock, Shares Issued	0	0
Preferred stock, Shares Outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, authorized	250,000,000	250,000,000
Common stock, Issued	25,388,643	25,401,479
Common stock, outstanding	25,388,643	25,401,479

Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 338	$ 354
Operating expenses:
Research and development	10,384	8,361
General and administrative	3,651	3,629
Total operating expenses	14,035	11,990
Loss from operations	(13,697)	(11,636)
Other income (expense):
Interest and investment income	757	486
Interest expense	(7)	(14)
Other expense	1	(1)
Other income (expense), net	751	471
Net loss	$ (12,946)	$ (11,165)
Net loss per share attributable to common shareholders - basic and diluted	$ (0.51)	$ (0.55)
Weighted-average common shares used in computing net loss per share attributable to common shareholders - basic and diluted	25,293,791	20,145,881
Comprehensive loss:
Net loss	$ (12,946)	$ (11,165)
Net unrealized gains (losses) on marketable securities	104	(102)
Comprehensive loss	$ (12,842)	$ (11,267)

Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock $0.001 Par	Additional Paid-in Capital	Other Accumulated Comprehensive Income	Accumulated Deficit
Balance at Dec. 31, 2017	$ 85,038	$ 16	$ 156,685	$ (9)	$ (71,654)
Balance (in Shares) at Dec. 31, 2017		16,272,617
Effect of adoption of ASU \| ASU 2014-09 (ASC 606)	324				324
Sale of common stock	53,753	$ 6	53,747
Sale of common stock, shares		5,899,500
Equity-based compensation expense	919		919
Unrealized gain (loss) on securities	(102)			(102)
Net loss	(11,165)				(11,165)
Balance at Mar. 31, 2018	128,767	$ 22	211,351	(111)	(82,495)
Balance (in Shares) at Mar. 31, 2018		22,172,117
Balance at Dec. 31, 2018	124,098	$ 25	243,903	(65)	(119,765)
Balance (in Shares) at Dec. 31, 2018		25,401,479
Cancellation of restricted stock		(12,836)
Equity-based compensation expense	954		954
Unrealized gain (loss) on securities	104			104
Net loss	(12,946)				(12,946)
Balance at Mar. 31, 2019	$ 112,210	$ 25	$ 244,857	$ 39	$ (132,711)
Balance (in Shares) at Mar. 31, 2019		25,388,643

Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Statement Of Stockholders Equity [Abstract]
Common stock, par value	$ 0.001	$ 0.001	$ 0.001

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (12,946)	$ (11,165)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	904	681
Loss on disposal of property and equipment		2
Equity-based compensation expense	954	919
Accretion/amortization of investment securities	(446)	(171)
Changes in operating assets and liabilities:
Accounts receivable	(2,500)
Prepaid expenses and other current assets	152	(493)
Accounts payable and accrued expenses	(1,084)	(2,975)
Deferred revenue	2,161	(354)
Operating lease liability	(313)
Deferred rent		295
Other assets		230
Net cash used in operating activities	(13,118)	(13,031)
Cash flows from investing activities:
Purchases of marketable securities	(39,346)	(74,964)
Proceeds from maturity of marketable securities	57,282	5,000
Purchases of property and equipment	(261)	(1,904)
Net cash provided by (used in) investing activities	17,675	(71,868)
Cash flows from financing activities:
Payments on finance lease obligations	(65)	(108)
Proceeds from sale of common stock, net of issuance costs		53,752
Net cash (used in) provided by financing activities	(65)	53,644
Net increase (decrease) in cash, cash equivalents and restricted cash	4,492	(31,255)
Cash, cash equivalents and restricted cash at beginning of period	12,349	59,537
Cash, cash equivalents and restricted cash at end of period	16,841	28,282
Supplemental disclosure of non-cash investing activities:
Landlord funded allowance for tenant improvements		1,653
Property and equipment purchases included in accounts payable and accrued expenses	(71)	1,047
Supplemental disclosure of non-cash financing activities:
Cash paid for interest	$ 7	$ 14

Nature of Business

3 Months Ended

Mar. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Business

(1)	Nature of Business

Organization

Synlogic, Inc., together with its wholly owned and consolidated subsidiaries (“Synlogic” or the “Company”), is a clinical-stage biopharmaceutical company focused on advancing its drug discovery and development platform for Synthetic Biotic™ medicines. Synthetic Biotic medicines are generated from Synlogic’s proprietary drug discovery and development platform applying the principles and tools of synthetic biology to engineer beneficial microbes to perform or deliver critical therapeutic functions to treat metabolic and inflammatory diseases and cancer. As living medicines, Synthetic Biotic medicines can be designed to sense a local disease context within a patient’s body and to respond by metabolizing a toxic substance, by compensating for missing or damaged metabolic pathways in patients, or by delivering combinations of therapeutic factors. Synlogic’s goal is to lead in the discovery and development of Synthetic Biotic therapies as living medicines capable of robust and precise pathway complementation and delivery of therapeutic benefit. Since incorporation, the Company has devoted substantially all of its efforts to the research and development of its product candidates.

Synlogic, Inc. (“Private Synlogic” when referred to prior to the Merger (as defined below)) was founded and began operations on March 14, 2014, as TMC Therapeutics, Inc., located in Cambridge, Massachusetts. On July 15, 2014, TMC Therapeutics, Inc. changed its name to Synlogic, Inc. On July 2, 2015, the common and preferred stockholders of Private Synlogic executed the Synlogic, LLC Contribution Agreement (the “Contribution Agreement”), pursuant to which such common and preferred stockholders contributed such stockholders’ equity interests in Private Synlogic in exchange for common and preferred units in a newly formed parent company named Synlogic, LLC. In addition, Synlogic IBDCo, Inc. (“IBDCo”) was formed as a subsidiary of Synlogic, LLC (the “2015 Reorganization”). In conjunction with the 2015 Reorganization, Private Synlogic entered into a license, option and merger agreement with AbbVie S.à.r.l. (“AbbVie”), for the development of treatments for inflammatory bowel disease (“IBD”). See Note 9, AbbVie Collaboration Agreement.

In May 2017, Private Synlogic completed a reorganization (the “2017 Reorganization”) pursuant to which Synlogic, LLC merged with and into Private Synlogic, with Private Synlogic continuing as the surviving corporation.

On August 28, 2017, Synlogic, Inc., formerly known as Mirna Therapeutics, Inc. (NASDAQ: MIRN) (“Mirna”), completed its business combination with Private Synlogic pursuant to the Agreement and Plan of Merger and Reorganization, dated as of May 15, 2017, by and among Mirna, Meerkat Merger Sub, Inc. (“Merger Sub”), and Private Synlogic (the “Merger Agreement”), pursuant to which Merger Sub merged with and into Private Synlogic, with Private Synlogic surviving as a wholly owned subsidiary of Mirna (the “Merger”). Immediately after completion of the Merger, Mirna changed its name to “Synlogic, Inc.” (NASDAQ: SYBX).

Risks and Uncertainties

At March 31, 2019, the Company had approximately $109.8 million in cash, cash equivalents, and marketable securities, $1.1 million of restricted cash and an accumulated deficit of approximately $132.7 million. Since its inception through March 31, 2019, the Company has primarily financed its operations through the issuance of preferred stock and units, the sale of its common stock, the AbbVie collaboration, and cash received in the Merger. In the absence of positive cash flows from operations, the Company is highly dependent on its ability to find additional sources of funding in the form of debt or equity financing. Management believes that the Company has sufficient cash to fund its operations through at least twelve months from the issuance of these financial statements.

As an early-stage company, the Company is subject to a number of risks common to other life science companies, including, but not limited to, raising additional capital, development by its competitors of new technological innovations, risk of failure in preclinical and clinical studies, safety and efficacy of its product candidates in clinical trials, the risk of relying on external parties such as contract research organizations (“CROs”) and contract manufacturing organizations (“CMOs”), the regulatory approval process, market acceptance of the Company’s products once approved, lack of marketing and sales history, dependence on key personnel and protection of proprietary technology. The Company’s therapeutic programs are currently pre-commercial, spanning discovery through early development and will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization of any product candidates. These efforts require significant amounts of additional capital, adequate personnel, infrastructure, and extensive compliance-reporting capabilities. 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, that any products developed will obtain necessary 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 revenue from product sales. The Company may never achieve profitability, and unless and until it does, it will continue to need to raise additional capital or obtain financing from other sources, such as strategic collaborations or partnerships.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

(2)	Summary of Significant Accounting Policies

The significant accounting policies described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s 2018 Annual Report for the year ended December 31, 2018, filed with the Securities and Exchange Commission (“SEC”) on March 12, 2019 (the “2018 Annual Report”), have had no material changes during the three months ended March 31, 2019, other than our adoption of ASU 2016-02 and ASU 2018-07 (as defined below). The updated accounting policies and the impact of adoption are each discussed in the “Recently Adopted Accounting Pronouncements” section in this note.

Basis of Presentation

The accompanying consolidated financial statements and the related disclosures as of March 31, 2019 and for the three months ended March 31, 2019 and 2018 are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) and the rules and regulations of the SEC for interim financial statements. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. These interim consolidated financial statements should be read in conjunction with the Company’s 2018 and 2017 audited consolidated financial statements and notes included in the Company’s 2018 Annual Report. The December 31, 2018 consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures including notes required by GAAP for complete financial statements. In the opinion of management, the unaudited interim consolidated financial statements reflect all adjustments, consisting of normal and recurring adjustments, necessary for the fair presentation of the Company’s financial position and results of operations for the three months ended March 31, 2019 and 2018. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or any other interim period or future year or period.

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of Synlogic and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02 – Leases (Topic 842), which replaces the existing accounting guidance for leases. This standard requires entities that lease assets to recognize the assets and liabilities for the rights and obligations created by those leases on the balance sheet. The standard is effective for fiscal years and the interim periods within those fiscal years beginning after December 15, 2018. The guidance is required to be applied by the modified retrospective transition approach and early adoption is permitted. In July 2018, the FASB issued ASU 2018-11 Leases – Targeted Improvements, intended to ease the implementation of the new lease standard for financial statement preparers by, among other things, allowing for an additional transition method. In lieu of presenting transition requirements to comparative periods, as previously required, an entity may now elect to show a cumulative effect adjustment on the date of adoption without the requirement to recast prior period financial statements or disclosures presented in accordance with ASU 2016-02. The Company adopted the new standard using the cumulative effect adjustment transition option effective January 1, 2019, which is the initial date of application per ASU 2018-11.

The Company elected the available package of practical expedients which allows the Company to not reassess previous accounting conclusions around whether arrangements are or contain leases, the classification of our leases, and the treatment of initial direct costs. The Company made an accounting policy election to keep leases with an initial term of 12 months or less off of the balance sheet.

The Company adopted ASU 2016-02: Leases (Topic 842) as of January 1, 2019. The Company uses judgement to assess if an arrangement is a lease at contract inception. An arrangement is a lease if the contract involves the use of a distinct identified asset, the lessor does not have substantive substitution rights and the Company obtains control of the asset throughout the period by obtaining substantially all of the economic benefit of the asset and the right to direct the use of the asset. Leases classified as operating leases are included in operating lease right-of-use (ROU) assets, current operating lease liabilities and noncurrent operating lease liabilities in our consolidated balance sheet. Finance leases are included in property and equipment and finance lease obligations, in our consolidated balance sheet.

ROU assets represent the right to use an underlying asset for the lease term and lease liabilities represent the obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the estimated present value of lease payments over the lease term. The Company utilizes its incremental borrowing rate to determine the present value of lease payments. The incremental borrowing rate is the rate incurred to borrow similar funds, on a collateralized basis, over a comparable term in a similar economic environment.

For new and amended leases beginning in 2019 and after, the Company has elected to account for the lease and non-lease components for leases as a single component for classes of all underlying assets and allocate all of the contract consideration to the lease component only. Lease cost for operating leases is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. Variable lease payments are included in lease operating expenses.

The lease term includes options to extend the lease when it is reasonably certain that option will be exercised. Leases with a term of 12 months or less are not recorded on the Company’s consolidated balance sheet.

The adoption had a material impact on the consolidated balance sheet related to the recognition of a transition adjustment on January 1, 2019 of a right-of-use asset of $15.9 million and lease liability of $24.0 million for an operating lease and the derecognition of deferred rent originally accounted for under legacy guidance. The adoption did not have a material impact on the consolidated statement of operations. The Company has designed and implemented changes to related processes, controls and disclosures. Refer to the Commitments and Contingencies footnote for further information on the adoption of this standard and the Company’s accounting for leases.

In February 2018, the FASB issued ASU 2018-02 – Income Statement – Reporting Comprehensive Income (Topic 220), which provides amended guidance on income tax accounting. The amended guidance permits the reclassification of the income tax effect on amounts recorded within other comprehensive income impacted by the Tax Cuts and Jobs Act (the “TCJA”) into retained earnings. The amended guidance is effective for periods beginning after December 15, 2018 and applies only to those amounts remaining in other comprehensive income at the date of enactment of the TCJA. The amended guidance may be adopted on either a retrospective basis or at the beginning of the period of adoption. The amended standard had an immaterial impact on the Company’s consolidated financial statements and as such the Company did not reclassify the income tax effects of the TCJA from other comprehensive income to retained earnings.

In June 2018, the FASB issued ASU 2018-07- Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. The standard is effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. Early adoption is permitted, but no earlier than an entity’s adoption date of ASC 606. The standard expands the scope of ASC 718 to include all share-based payment arrangements related to the acquisition of goods and services from both nonemployees and employees. Under the amended guidance, equity-classified share-based payment awards issued to nonemployees will be measured at grant date fair value. Upon transition, the entity is required to remeasure these nonemployee awards at fair value as of the adoption date. The Company adopted the new guidance January 1, 2019 which had an immaterial impact on its consolidated financial statements.

Recently Issued Accounting Pronouncements

In August 2018, the FASB issued ASU 2018-13 - Fair Value Measurement - Disclosure Framework (Topic 820). The standard modifies the disclosure requirements for fair value measurements. The standard is effective for public companies for annual and interim periods beginning after December 15, 2019. Early adoption is permitted for any removed or modified disclosures. Management is currently assessing the impact adoption will have on the Company, but it is not expected to have a material impact on the Company’s financial statement disclosures.

In August 2018, the FASB issued ASU 2018-15 - Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract. The standard requires implementation costs incurred by customers in cloud computing arrangements to be deferred over the noncancelable term of the cloud computing arrangements plus any optional renewal periods (1) that are reasonably certain to be exercised by the customer or (2) for which exercise of the renewal option is controlled by the cloud service provider. The effective date of this pronouncement is for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, and early adoption is permitted. The standard can be adopted either using the prospective or retrospective transition approach. The Company is currently evaluating the impact of this standard on the Company's consolidated financial statements and disclosures.

In November 2018, the FASB issued ASU 2018-18 - Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606, which, among other things, provides guidance on how to assess whether certain collaborative arrangement transactions should be accounted for under Topic 606. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the impact of this standard on the Company’s consolidated financial statements.

Fair Value of Financial Instruments

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

(3)	Fair Value of Financial Instruments

The tables below present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value, as described under Note 2, Summary of Significant Accounting Policies, in the audited financial statements included in the Company’s 2018 Annual Report.

The Company’s investment portfolio includes many fixed income securities that do not always trade on a daily basis. As a result, the pricing services used by the Company applied other available information as applicable through processes such as benchmark yields, benchmarking of like securities, sector groupings and matrix pricing to prepare evaluations. In addition, model processes were used to assess interest rate impact and develop prepayment scenarios. These models take into consideration relevant credit information, perceived market movements, sector news and economic events. The inputs into these models may include benchmark yields, reported trades, broker-dealer quotes, issuer spreads and other relevant data.

At March 31, 2019 and December 31, 2018, the Company has classified assets measured at fair value on a recurring basis as follows (in thousands):

	Fair Value Measurements at March 31, 2019
	March 31,		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Description	2019		(Level 1)		(Level 2)		(Level 3)
Money market funds (included in cash and cash equivalents)	$	870	$	870	$	—	$	—
Corporate debt securities (included in cash and cash equivalents)		5,749		—		5,749		—
Corporate debt securities (included in short-term investments)		90,101		—		90,101		—
U.S. government agency securities and treasuries (included in short-term investments)		3,990		1,994		1,996		—
Total	$	100,710	$	2,864	$	97,846	$	—

	Fair Value Measurements at December 31, 2018
	December 31,		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Description	2018		(Level 1)		(Level 2)		(Level 3)
Money market funds (included in cash and cash equivalents)	$	265	$	265	$	—	$	—
Corporate debt securities (included in short-term investments)		107,505		—		107,505		—
U.S. government agency securities and treasuries (included in short-term investments)		3,972		1,987		1,985		—
Total	$	111,742	$	2,252	$	109,490	$	—

Cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses at March 31, 2019 and December 31, 2018 are carried at amounts that approximate fair value due to their short-term maturities. Finance lease obligations at March 31, 2019 and December 31, 2018 approximate fair value as they bear interest at a rate approximating a market interest rate.

- 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

Available-for-Sale Investments

3 Months Ended

Mar. 31, 2019

Investments Debt And Equity Securities [Abstract]

Available-for-Sale Investments

(4)	Available-for-Sale Investments

The following tables summarize the available-for-sale securities held at March 31, 2019 and December 31, 2018 (in thousands):

March 31, 2019	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair Value
Corporate debt securities	$	90,062	$	42	$	(3	)	$	90,101
U.S. government agency and treasury securities	$	3,990	$	—	$	—		$	3,990
Total	$	94,052	$	42	$	(3	)	$	94,091

December 31, 2018	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair Value
Corporate debt securities	$	107,571	$	4	$	(70	)	$	107,505
U.S. government agency securities	$	3,971	$	1	$	—		$	3,972
Total	$	111,542	$	5	$	(70	)	$	111,477

The contractual maturity of all securities held at March 31, 2019 was one year or less. There were 19 and 37 investments in an unrealized loss position at March 31, 2019 and December 31, 2018, respectively, none of which had been in an unrealized loss position for more than twelve months. The aggregate fair value of the securities in an unrealized loss position at March 31, 2019 and December 31, 2018 was $35.6 million and $96.5 million, respectively. The Company reviews its investments for other-than-temporary impairment whenever the fair value of an investment is less than amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other-than-temporary, the Company considers whether it has the ability and intent to hold the investment until a market price recovery and considers whether evidence indicating the cost of the investment is recoverable outweighs evidence to the contrary. The Company did not hold any securities with an other-than-temporary impairment at March 31, 2019.

Gross realized gains and losses on the sales of investments have not been material to the Company’s consolidated statement of operations.

Property and Equipment, Net

3 Months Ended

Mar. 31, 2019

Property Plant And Equipment [Abstract]

Property and Equipment, Net

(5)	Property and Equipment, net

Property and equipment, net consists of the following (in thousands):

	March 31,			December 31,
	2019			2018
Laboratory equipment	$	7,287		$	7,111
Computer and office equipment		829			781
Furniture and fixtures		413			413
Leasehold improvements		9,484			9,484
Construction in progress		5			39
		18,018			17,828
Less accumulated depreciation		(3,670	)		(2,987	)
	$	14,348		$	14,841

Accrued Expenses

3 Months Ended

Mar. 31, 2019

Payables And Accruals [Abstract]

Accrued Expenses

(6)	Accrued Expenses

Accrued expenses consists of the following (in thousands):

	March 31,		December 31,
	2019		2018
Payroll related	$	1,165	$	2,906
Professional fees		544		306
Research and development		2,023		1,585
Other		149		237
	$	3,881	$	5,034

Common Stock

3 Months Ended

Mar. 31, 2019

Equity [Abstract]

Common Stock

(7)	Common Stock

The Company’s common stock has the following characteristics:

•

The holders of shares of common stock are entitled to one vote for each share of common stock held at all meetings of stockholders.

•

The holders of shares of common stock are entitled to receive dividends, if and when, declared by the Company’s board of directors. Since inception, no cash dividends have been declared.

Equity-based Compensation and Equity Incentive Plans

3 Months Ended

Mar. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity-based Compensation and Equity Incentive Plans

(8)	Equity‑based Compensation and Equity Incentive Plans

The Company is displaying all equity in its post-Merger amounts.

Equity Plans

The Company has a number of equity plans, two of which are currently active.

The 2015 Equity Incentive Award Plan (the “2015 Plan”) was adopted by Mirna in 2015 and remains active after the Merger, now functioning as the primary equity plan for the Company. The 2015 Plan provides for the granting of a variety of stock‑based compensation awards, including stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, deferred stock awards, dividend equivalent awards, stock payment awards, performance awards and other stock‑based awards. Pursuant to the evergreen provision of the 2015 Plan, which allows for an annual increase in the number of shares of common stock available for issuance, the Company added 1,270,073 shares to the 2015 Plan on January 1, 2019.

The 2017 Stock Incentive Plan (the “2017 Plan”) was adopted by Private Synlogic in 2017 at the time of the 2017 Reorganization and assumed by the Company during the Merger. The 2017 Plan provides for the grant of incentive stock options, non-qualified stock options, restricted and unrestricted stock awards and other stock-based awards.

As of March 31, 2019, there were 753,164 shares available for future grant under the Company’s two active equity incentive plans, the 2017 Plan and the 2015 Plan.

For a full description of the Company’s equity plans, refer to Note 12, Equity-based Compensation and Equity Incentive Plans in the Company’s 2018 Annual Report.

Stock Options

The following table summarizes stock option activity during the three months ended March 31, 2019 under the 2015 Plan and the 2017 Plan.

	Stock options outstanding
						Weighted
				Weighted		average		Aggregate
				average		remaining		Intrinsic
	Number of			exercise		contractual		value^(a)
	options			price		term (in years)		(in thousands)
Outstanding at December 31, 2018		1,739,884		$	11.92		9.0	$	—
Granted		1,163,980			8.54
Exercised		—			—
Forfeited		(156,821	)		13.84
Outstanding at March 31, 2019		2,747,043			10.38		9.2	$	2,030

Vested or expected to vest at March 31, 2019		2,747,043			10.38		9.2		2,030

Exercisable at March 31, 2019		558,274			13.10		8.5	$	—

(a)

The aggregate intrinsic value is calculated as the difference between the exercise price of the options and the fair market value of the underlying common stock for the options that were in the money at March 31, 2019 and December 31, 2018.

As of March 31, 2019, there was $12.7 million of unrecognized share-based compensation related to unvested stock option grants which is expected to be recognized over a weighted average period of 3.1 years. The total unrecognized share-based compensation cost will be adjusted for actual forfeitures as they occur.

Restricted Common Stock

The following table shows restricted stock activity during the three months ended March 31, 2019:

	Restricted stock awards
				Grant date
	Number of			fair value
	shares			(per share)
Unvested at December 31, 2018		118,679		$	13.54
Granted		—			—
Vested		(18,124	)		13.53
Forfeited		(12,836	)		13.53
Unvested at March 31, 2019		87,719		$	13.55

As of March 31, 2019, there was approximately $0.1 million of unrecognized share-based compensation related to restricted stock awards granted, which is expected to be recognized over a weighted average period of 1.4 years. The total unrecognized share-based compensation cost will be adjusted for actual forfeitures as they occur.

Equity Compensation

The Company recorded total equity-based compensation expense of $1.0 million during the three months ended March 31, 2019, and $0.9 million during the three months ended March 31, 2018.

The following table summarizes equity‑based compensation expense within the Company’s consolidated statements of operations and comprehensive loss for the three months ended March 31, 2019 and 2018 (in thousands):

	Three Months Ended March 31,
	2019		2018
Research and development	$	284	$	377
General and administrative		670		542
	$	954	$	919

The following table summarizes equity‑based compensation expense by type of award for the three months ended March 31, 2019 and 2018 (in thousands):

	Three Months Ended March 31,
	2019		2018
Stock options	$	926	$	773
Restricted stock awards		28		146
	$	954	$	919

AbbVie Collaboration Agreement

3 Months Ended

Mar. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

AbbVie Collaboration Agreement

(9)	AbbVie Collaboration Agreement

In July 2015, the Company entered into the AbbVie Agreement under which the Company granted AbbVie an exclusive option to purchase IBDCo and, in exchange, agreed to collaborate in researching and developing an Investigational New Drug (“IND”) candidate for the treatment of IBD. The AbbVie Agreement sets forth the Company’s and AbbVie’s respective obligations for development and delivery of an IND candidate package using reasonable commercial efforts.

In exchange for the exclusive option to acquire IBDCo, initial research and development services for drug discovery and pre-clinical development, and participation on the joint research committee (“JRC”), AbbVie agreed to pay IBDCo an upfront, nonrefundable cash payment of $2.0 million, which IBDCo received in December 2015. AbbVie also agreed to pay IBDCo up to $16.5 million in milestone payments associated with specified research and pre-clinical events, which were determined to represent customer options for accounting purposes, as well as an option exercise fee upon the execution of their option to buy IBDCo and other royalty and milestone payments. The upfront cash payment and any payments for option fees and royalties are non-refundable, non-creditable and not subject to set-off.

The research and development will be performed by the Company over four phases of research defined in the research plan. The Company is eligible to receive payments from AbbVie upon the election to continue the research and development at the achievement of certain milestone events. The JRC will make a determination as to the continuation of the collaboration at the achievement of research and pre-clinical milestones, except for the final milestone, which AbbVie has the discretion to determine achievement without the approval of the JRC. If the parties make the determination to continue on with the AbbVie Agreement upon achievement of each milestone event, then AbbVie will pay the consideration associated with that milestone and the collaboration will continue through the remaining term of the option to purchase IBDCo, which was initially considered to be approximately 54 months. However, AbbVie has the right to terminate the contract at any time with 90 days’ notice.

The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, AbbVie, is a customer. The Company identified the following material promises at the outset of the arrangement: (1) a non-exclusive royalty-free research and development license; (2) research and development services for pre-clinical activities under the research plan through to the first research and development phase (or an estimated 17 months); (3) three option rights for AbbVie to continue the collaboration as related to three phases of research and development; (4) participation on the JRC; and (5) the transfer of ownership of IBDCo upon exercise of the option to buy IBDCo. The Company determined that the license and research and development activities were not distinct from one another. Participation on the JRC to oversee the research and development activities was determined to be quantitatively and qualitatively immaterial and therefore is excluded from performance obligations. As such, the Company determined that the license and research and development services should be combined into a single performance obligation.

The Company evaluated the milestone payments, which represent customer options as described above, and the option to purchase IBDCo, to determine whether they provide AbbVie with any material rights. The Company concluded that the options were not issued at a significant and incremental discount, and therefore do not provide material rights. As such, they were excluded as performance obligations at the outset of the arrangement. If AbbVie elects to exercise the options, the additional consideration will be added to the transaction price and allocated to the resulting performance obligations.

Based on these assessments, the Company identified one performance obligation at the outset of the AbbVie Agreement, which consists of: (1) the non-exclusive license and (2) the research and development activities through the first research and development phase.

At the outset of the arrangement, the transaction price included only the $2.0 million up-front consideration received which was allocated to the single performance obligation. The option exercise fees ($16.5 million for the milestones and the IBDCo purchase option exercise fee) that may be received are excluded from the transaction price until each customer option is exercised. The Company reevaluates the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, adjust its estimate of the transaction price.

In May 2017, the Company completed the research and development services for the first phase of the research plan and was paid $2.0 million to commence the second phase of the research plan. At this time, the $2.0 million was added to the transaction price and allocated to a new performance obligation consisting of the underlying license and research and development services to be performed over the second phase of the research plan.

On September 27, 2018, AbbVie and the Company signed an amendment (the “Amendment”) to the AbbVie Agreement. The Amendment clarified the requirements necessary to complete the second phase which resulted in additional time and effort in the second phase of the research plan. Additionally, the Amendment split the next milestone payment under the AbbVie Agreement into two payments: a milestone payment of $2.0 million earned by the Company upon execution of the Amendment and the remaining milestone payment of the balance due upon the successful achievement of specified research and pre-clinical events and the advancement to the third phase of the research plan.

On December 18, 2018, AbbVie and the Company signed an amendment (the “Third Amendment”) to the AbbVie Agreement. The Third Amendment provides that in the event AbbVie determines that it is necessary to enter into license agreements with certain third parties in a particular country or other jurisdiction which, but for such license, would be infringed by the manufacture, use or sale of any product governed by the AbbVie Agreement, AbbVie would be entitled to deduct certain expenses related to such license agreements from particular payments made to the Company.

The Company determined that the Amendment represented a modification to the AbbVie Agreement. The additional research and development services are not distinct from the remaining research and development services under the second phase of the research plan of the AbbVie Agreement. The Amendment was accounted for as part of the original AbbVie Agreement and the services form part of the single performance obligation that was partially satisfied as of the date of the contract modification. As a result, the transaction price for the current performance obligation associated with the second phase of the research plan increased by $2.0 million. The impact of the contract modification on the transaction price and the measure of progress toward completion of the performance obligation was recognized as an adjustment to revenue upon execution of the Amendment on a cumulative catch-up basis.

On February 28, 2019, the JRC concluded that the remaining milestone of $2.5 million under the Second Amendment was achieved upon the achievement of specified research and pre-clinical events under the second phase of the research plan and the advancement to the third phase of the research plan. Revenue associated with performance obligations under the AbbVie Agreement are recognized as the research and development services are provided using an input method, according to the full time equivalents incurred. The transfer of control occurs over time and, in management’s judgment, is the best measure of progress towards satisfying the performance obligation. The amounts received that have not yet been recognized as revenue are recorded in deferred revenue on the Company’s consolidated balance sheet.

For the three months ended March 31, 2019 and 2018, the Company recognized revenue of $0.3 million and $0.4 million, respectively, as collaboration revenue in the Company’s consolidated statements of operations and comprehensive loss. The deferred revenue balance as of December 31, 2018 was fully recognized during the three months ended March 31, 2019. Long term and current deferred revenue amounted to $2.0 million and $0.5 million, respectively, as of March 31, 2019.

Net Loss per Share

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

Net Loss per Share

(10)	Net Loss per Share

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

The Company computed basic and diluted net loss per share using the two-class method, which gives effect to the impact of outstanding participating securities. As the three months ended March 31, 2019 and 2018 resulted in net losses attributable to common stockholders, there is no income allocation required under the two-class method or dilution attributed to weighted-average shares outstanding in the calculation of diluted net loss per share because the preferred stockholders do not participate in losses of the Company. Accordingly, for 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 stock are not assumed to have been issued if their effect is anti-dilutive.

The Company’s potentially dilutive shares, which include outstanding stock options and unvested restricted common stock/units, are considered to be common share equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive.

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

	As of March 31,
	2019		2018
Unvested restricted common stock awards		87,719		320,166
Outstanding options to purchase common stock		2,747,043		1,741,527

Commitments and Contingencies

3 Months Ended

Mar. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

(11)	Commitments and Contingencies

In the ordinary course of business, the Company may be subject to legal proceedings, claims and litigation as the Company operates in an industry susceptible to patent legal claims. The Company accounts for estimated losses with respect to legal proceedings and claims when such losses are probable and estimable. Legal costs associated with these matters are expensed when incurred. The Company is not currently a party to any material legal proceedings.

In July 2017, the Company entered into an agreement to lease approximately 41,346 square feet of laboratory and office space at 301 Binney Street in Cambridge, Massachusetts. Annual rent is approximately $3.1 million. The ten-year lease commenced in January 2018 and contains provisions for a free-rent period, annual rent increases and an allowance for tenant improvements. Additionally, we have paid for a tenant improvement investment of approximately $1.6 million. The Company was determined to be the accounting owner and recorded tenant improvements as leasehold improvements which reduce the initial measurement of the ROU asset. In conjunction with the lease, we established a letter of credit of approximately $1.0 million. Variable payments based on our portion of the operating expenses, including real estate taxes and insurance, are recorded as a period expense when incurred. The Company has an option to extend the term by five years and an option to terminate the agreement if a similar agreement is executed with the landlord or an affiliate of the landlord. Neither option is reasonably certain of exercise and are excluded from the lease liability calculation.

On December 7, 2018, Synlogic Operating Company, Inc., a wholly-owned subsidiary of Synlogic, Inc., entered into a Statement of Work (the “SOW”) with Azzur Group, LLC (“Azzur”) pursuant to a Master Contract Services Agreement (the “Master Services Agreement”), dated September 8, 2018, between the Company and Azzur.

Pursuant to the SOW, Azzur has agreed to provide the Company with access to, and the use of, an approximately 700 square foot cleanroom space to be constructed in Waltham, Massachusetts (the “Azzur Suite”), for a period of 44 months, from May 1, 2019 to December 31, 2022 (the “Term”). Azzur has also agreed to provide the Company with storage space and personnel support at the Azzur Suite. The total estimated project cost during the Term for access to, and use of, the cleanroom and storage space, and the personnel support and other services, is up to $4.8 million.

The Company may terminate the SOW on four months’ prior written notice at any time during the Term. In addition, either party may terminate the Master Services Agreement (including the SOW) due to a breach by the other party and failure to cure. If the Azzur Suite is not ready for use by the Company as of May 1, 2019, the Company may (i) elect to terminate the SOW, (ii) wait for the Azzur Suite to become available, without incurring any costs (other than a deposit) relating to the Azzur Suite until it becomes available, or (iii) accept an alternate cleanroom space from Azzur on different terms. As the lease has not yet commenced, the financial terms of the arrangement are not included in the schedules below.

The operating lease right-of-use asset and operating lease liability represents the Binney Street lease. Finance leases are made up of laboratory and office equipment. Cash paid for amounts included in the present value of operating lease liabilities was $0.8 million during the three months ended March 31, 2019 which is included in operating cash flows.

The components of lease cost for operating and finance leases for the three months ended March 31, 2019 were:

Operating leases	$ (in thousands)
Operating lease cost	$	694
Variable lease cost		263
		957
Short-term lease cost		119

Finance leases
Depreciation on finance leases		47
Interest on finance leases		7
		54
Total lease cost	$	1,130

The right-of-use asset for the operating lease is disclosed on the consolidated balance sheet. The right-of-use asset for finance leases are classified within property and equipment, net, the total right-of-use asset for finance leases is $0.9 million:

The weighted average remaining lease term and the weighted average discount rate for operating and finance leases at March 31, 2019 was:

	Operating Lease			Finance Leases
Weighted average discount rate		9.0	%		5.9	%
Weighted average remaining lease term (years)	9.4			1.5

The following table reconciles the undiscounted cash flows for the operating and finance leases at March 31, 2019 to the operating and finance lease liabilities recorded on the balance sheet:

Maturity of lease liabilities	Operating Lease		Finance Leases
	(in thousands)
2019	$	2,390	$	215
2020		3,270		214
2021		3,369		2
2022		3,470		-
2023		3,574		-
Thereafter		18,067		-
Total lease payments		34,140		431
Less: imputed interest		10,449		21
Total lease liabilities	$	23,691	$	410

Current lease liabilities		1,374		269
Long-term lease liabilities		22,317		141

The aggregate future lease payments for operating and capital leases as of December 31, 2018 are as follows:

	Operating lease		Capital leases
	(in thousands)
2019	$	3,175	$	287
2020		3,270		214
2021		3,369		2
2022		3,470		—
2023		3,574		—
Thereafter		18,067		—
Total future minimum lease payments	$	34,925	$	503
Less amounts representing interest				27
Capital lease obligations at December 31, 2018				476
Less current portion of capital lease obligations				266
Capital lease obligations, net of current portion			$	210

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements and the related disclosures as of March 31, 2019 and for the three months ended March 31, 2019 and 2018 are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) and the rules and regulations of the SEC for interim financial statements. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. These interim consolidated financial statements should be read in conjunction with the Company’s 2018 and 2017 audited consolidated financial statements and notes included in the Company’s 2018 Annual Report. The December 31, 2018 consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures including notes required by GAAP for complete financial statements. In the opinion of management, the unaudited interim consolidated financial statements reflect all adjustments, consisting of normal and recurring adjustments, necessary for the fair presentation of the Company’s financial position and results of operations for the three months ended March 31, 2019 and 2018. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or any other interim period or future year or period.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Synlogic and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02 – Leases (Topic 842), which replaces the existing accounting guidance for leases. This standard requires entities that lease assets to recognize the assets and liabilities for the rights and obligations created by those leases on the balance sheet. The standard is effective for fiscal years and the interim periods within those fiscal years beginning after December 15, 2018. The guidance is required to be applied by the modified retrospective transition approach and early adoption is permitted. In July 2018, the FASB issued ASU 2018-11 Leases – Targeted Improvements, intended to ease the implementation of the new lease standard for financial statement preparers by, among other things, allowing for an additional transition method. In lieu of presenting transition requirements to comparative periods, as previously required, an entity may now elect to show a cumulative effect adjustment on the date of adoption without the requirement to recast prior period financial statements or disclosures presented in accordance with ASU 2016-02. The Company adopted the new standard using the cumulative effect adjustment transition option effective January 1, 2019, which is the initial date of application per ASU 2018-11. The Company elected the available package of practical expedients which allows the Company to not reassess previous accounting conclusions around whether arrangements are or contain leases, the classification of our leases, and the treatment of initial direct costs. The Company made an accounting policy election to keep leases with an initial term of 12 months or less off of the balance sheet. The Company adopted ASU 2016-02: Leases (Topic 842) as of January 1, 2019. The Company uses judgement to assess if an arrangement is a lease at contract inception. An arrangement is a lease if the contract involves the use of a distinct identified asset, the lessor does not have substantive substitution rights and the Company obtains control of the asset throughout the period by obtaining substantially all of the economic benefit of the asset and the right to direct the use of the asset. Leases classified as operating leases are included in operating lease right-of-use (ROU) assets, current operating lease liabilities and noncurrent operating lease liabilities in our consolidated balance sheet. Finance leases are included in property and equipment and finance lease obligations, in our consolidated balance sheet. ROU assets represent the right to use an underlying asset for the lease term and lease liabilities represent the obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the estimated present value of lease payments over the lease term. The Company utilizes its incremental borrowing rate to determine the present value of lease payments. The incremental borrowing rate is the rate incurred to borrow similar funds, on a collateralized basis, over a comparable term in a similar economic environment. For new and amended leases beginning in 2019 and after, the Company has elected to account for the lease and non-lease components for leases as a single component for classes of all underlying assets and allocate all of the contract consideration to the lease component only. Lease cost for operating leases is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. Variable lease payments are included in lease operating expenses. The lease term includes options to extend the lease when it is reasonably certain that option will be exercised. Leases with a term of 12 months or less are not recorded on the Company’s consolidated balance sheet. The adoption had a material impact on the consolidated balance sheet related to the recognition of a transition adjustment on January 1, 2019 of a right-of-use asset of $15.9 million and lease liability of $24.0 million for an operating lease and the derecognition of deferred rent originally accounted for under legacy guidance. The adoption did not have a material impact on the consolidated statement of operations. The Company has designed and implemented changes to related processes, controls and disclosures. Refer to the Commitments and Contingencies footnote for further information on the adoption of this standard and the Company’s accounting for leases. In February 2018, the FASB issued ASU 2018-02 – Income Statement – Reporting Comprehensive Income (Topic 220), which provides amended guidance on income tax accounting. The amended guidance permits the reclassification of the income tax effect on amounts recorded within other comprehensive income impacted by the Tax Cuts and Jobs Act (the “TCJA”) into retained earnings. The amended guidance is effective for periods beginning after December 15, 2018 and applies only to those amounts remaining in other comprehensive income at the date of enactment of the TCJA. The amended guidance may be adopted on either a retrospective basis or at the beginning of the period of adoption. The amended standard had an immaterial impact on the Company’s consolidated financial statements and as such the Company did not reclassify the income tax effects of the TCJA from other comprehensive income to retained earnings. In June 2018, the FASB issued ASU 2018-07- Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. The standard is effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. Early adoption is permitted, but no earlier than an entity’s adoption date of ASC 606. The standard expands the scope of ASC 718 to include all share-based payment arrangements related to the acquisition of goods and services from both nonemployees and employees. Under the amended guidance, equity-classified share-based payment awards issued to nonemployees will be measured at grant date fair value. Upon transition, the entity is required to remeasure these nonemployee awards at fair value as of the adoption date. The Company adopted the new guidance January 1, 2019 which had an immaterial impact on its consolidated financial statements.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In August 2018, the FASB issued ASU 2018-13 - Fair Value Measurement - Disclosure Framework (Topic 820). The standard modifies the disclosure requirements for fair value measurements. The standard is effective for public companies for annual and interim periods beginning after December 15, 2019. Early adoption is permitted for any removed or modified disclosures. Management is currently assessing the impact adoption will have on the Company, but it is not expected to have a material impact on the Company’s financial statement disclosures. In August 2018, the FASB issued ASU 2018-15 - Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract. The standard requires implementation costs incurred by customers in cloud computing arrangements to be deferred over the noncancelable term of the cloud computing arrangements plus any optional renewal periods (1) that are reasonably certain to be exercised by the customer or (2) for which exercise of the renewal option is controlled by the cloud service provider. The effective date of this pronouncement is for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, and early adoption is permitted. The standard can be adopted either using the prospective or retrospective transition approach. The Company is currently evaluating the impact of this standard on the Company's consolidated financial statements and disclosures. In November 2018, the FASB issued ASU 2018-18 - Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606, which, among other things, provides guidance on how to assess whether certain collaborative arrangement transactions should be accounted for under Topic 606. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the impact of this standard on the Company’s consolidated financial statements.

Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of Company's Classified Assets Measured at Fair Value on Recurring Basis

the Company has classified assets measured at fair value on a recurring basis as follows (in thousands):

	Fair Value Measurements at March 31, 2019
	March 31,		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Description	2019		(Level 1)		(Level 2)		(Level 3)
Money market funds (included in cash and cash equivalents)	$	870	$	870	$	—	$	—
Corporate debt securities (included in cash and cash equivalents)		5,749		—		5,749		—
Corporate debt securities (included in short-term investments)		90,101		—		90,101		—
U.S. government agency securities and treasuries (included in short-term investments)		3,990		1,994		1,996		—
Total	$	100,710	$	2,864	$	97,846	$	—

	Fair Value Measurements at December 31, 2018
	December 31,		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Description	2018		(Level 1)		(Level 2)		(Level 3)
Money market funds (included in cash and cash equivalents)	$	265	$	265	$	—	$	—
Corporate debt securities (included in short-term investments)		107,505		—		107,505		—
U.S. government agency securities and treasuries (included in short-term investments)		3,972		1,987		1,985		—
Total	$	111,742	$	2,252	$	109,490	$	—

Available-for-Sale Investments (Tables)

3 Months Ended

Mar. 31, 2019

Investments Debt And Equity Securities [Abstract]

Summary of Available-for-Sale Securities Held

The following tables summarize the available-for-sale securities held at March 31, 2019 and December 31, 2018 (in thousands):

March 31, 2019	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair Value
Corporate debt securities	$	90,062	$	42	$	(3	)	$	90,101
U.S. government agency and treasury securities	$	3,990	$	—	$	—		$	3,990
Total	$	94,052	$	42	$	(3	)	$	94,091

December 31, 2018	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair Value
Corporate debt securities	$	107,571	$	4	$	(70	)	$	107,505
U.S. government agency securities	$	3,971	$	1	$	—		$	3,972
Total	$	111,542	$	5	$	(70	)	$	111,477

Property and Equipment, Net (Tables)

3 Months Ended

Mar. 31, 2019

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consists of the following (in thousands):

	March 31,			December 31,
	2019			2018
Laboratory equipment	$	7,287		$	7,111
Computer and office equipment		829			781
Furniture and fixtures		413			413
Leasehold improvements		9,484			9,484
Construction in progress		5			39
		18,018			17,828
Less accumulated depreciation		(3,670	)		(2,987	)
	$	14,348		$	14,841

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2019

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consists of the following (in thousands):

	March 31,		December 31,
	2019		2018
Payroll related	$	1,165	$	2,906
Professional fees		544		306
Research and development		2,023		1,585
Other		149		237
	$	3,881	$	5,034

Equity-based Compensation and Equity Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2019

Schedule of Restricted Common Stock Activity

The following table shows restricted stock activity during the three months ended March 31, 2019:

	Restricted stock awards
				Grant date
	Number of			fair value
	shares			(per share)
Unvested at December 31, 2018		118,679		$	13.54
Granted		—			—
Vested		(18,124	)		13.53
Forfeited		(12,836	)		13.53
Unvested at March 31, 2019		87,719		$	13.55

Schedule of Equity-based Compensation Expenses

	Three Months Ended March 31,
	2019		2018
Research and development	$	284	$	377
General and administrative		670		542
	$	954	$	919

Schedule of Equity-based Compensation Expenses by Award Type

The following table summarizes equity‑based compensation expense by type of award for the three months ended March 31, 2019 and 2018 (in thousands):

	Three Months Ended March 31,
	2019		2018
Stock options	$	926	$	773
Restricted stock awards		28		146
	$	954	$	919

2015 and 2017 Plan

Schedule of Stock Option Activity

The following table summarizes stock option activity during the three months ended March 31, 2019 under the 2015 Plan and the 2017 Plan.

	Stock options outstanding
						Weighted
				Weighted		average		Aggregate
				average		remaining		Intrinsic
	Number of			exercise		contractual		value^(a)
	options			price		term (in years)		(in thousands)
Outstanding at December 31, 2018		1,739,884		$	11.92		9.0	$	—
Granted		1,163,980			8.54
Exercised		—			—
Forfeited		(156,821	)		13.84
Outstanding at March 31, 2019		2,747,043			10.38		9.2	$	2,030

Vested or expected to vest at March 31, 2019		2,747,043			10.38		9.2		2,030

Exercisable at March 31, 2019		558,274			13.10		8.5	$	—

(a)

Net Loss per Share (Tables)

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

Schedule of Potentially Common Shares Excluded from Calculation of Net Loss Per share

	As of March 31,
	2019		2018
Unvested restricted common stock awards		87,719		320,166
Outstanding options to purchase common stock		2,747,043		1,741,527

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Components of Lease Cost for Operating and Finance Leases

The components of lease cost for operating and finance leases for the three months ended March 31, 2019 were:

Operating leases	$ (in thousands)
Operating lease cost	$	694
Variable lease cost		263
		957
Short-term lease cost		119

Finance leases
Depreciation on finance leases		47
Interest on finance leases		7
		54
Total lease cost	$	1,130

Summary of Weighted Average Remaining Lease Term and Weighted Average Discount Rate for Operating and Finance Leases

The weighted average remaining lease term and the weighted average discount rate for operating and finance leases at March 31, 2019 was:

	Operating Lease			Finance Leases
Weighted average discount rate		9.0	%		5.9	%
Weighted average remaining lease term (years)	9.4			1.5

Summary of Maturity of Lease Liabilities for Operating and Finance Leases

The following table reconciles the undiscounted cash flows for the operating and finance leases at March 31, 2019 to the operating and finance lease liabilities recorded on the balance sheet:

Maturity of lease liabilities	Operating Lease		Finance Leases
	(in thousands)
2019	$	2,390	$	215
2020		3,270		214
2021		3,369		2
2022		3,470		-
2023		3,574		-
Thereafter		18,067		-
Total lease payments		34,140		431
Less: imputed interest		10,449		21
Total lease liabilities	$	23,691	$	410

Current lease liabilities		1,374		269
Long-term lease liabilities		22,317		141

Schedule of Aggregate Future Lease Payments for Operating and Capital Leases

The aggregate future lease payments for operating and capital leases as of December 31, 2018 are as follows:

	Operating lease		Capital leases
	(in thousands)
2019	$	3,175	$	287
2020		3,270		214
2021		3,369		2
2022		3,470		—
2023		3,574		—
Thereafter		18,067		—
Total future minimum lease payments	$	34,925	$	503
Less amounts representing interest				27
Capital lease obligations at December 31, 2018				476
Less current portion of capital lease obligations				266
Capital lease obligations, net of current portion			$	210

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash, cash equivalents, and marketable securities	$ 109,800
Restricted cash	1,097	$ 1,097
Accumulated deficit	$ (132,711)	$ (119,765)

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jul. 31, 2017	Mar. 31, 2019	Jan. 01, 2019
Accounting Policies [Abstract]
Lease, practical expedients, package		true
Lessee, operating lease, existence of option to extend	true	true
Lessee, operating lease, option to extend		options to extend the lease when it is reasonably certain that option will be exercised
Operating lease, right-of-use asset		$ 15,698	$ 15,900
Operating lease, lease liability		$ 23,691	$ 24,000

Fair Value of Financial Instruments - Schedule of Company's Classified Assets Measured at Fair Value on Recurring Basis (Detail) - Recurring - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value Asset Measured On Recurring Basis [Line Items]
Total assets	$ 100,710	$ 111,742
Money market funds
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	870	265
Corporate debt securities
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	5,749
Short-term investments	90,101	107,505
U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	3,990	3,972
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Asset Measured On Recurring Basis [Line Items]
Total assets	2,864	2,252
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Money market funds
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	870	265
Quoted Prices in Active Markets for Identical Assets (Level 1) \| U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	1,994	1,987
Significant Other Observable Inputs (Level 2)
Fair Value Asset Measured On Recurring Basis [Line Items]
Total assets	97,846	109,490
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	5,749
Short-term investments	90,101	107,505
Significant Other Observable Inputs (Level 2) \| U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	1,996	1,985
Significant Unobservable Inputs (Level 3)
Fair Value Asset Measured On Recurring Basis [Line Items]
Total assets	0	0
Significant Unobservable Inputs (Level 3) \| Money market funds
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	0	0
Significant Unobservable Inputs (Level 3) \| Corporate debt securities
Fair Value Asset Measured On Recurring Basis [Line Items]
Cash and Cash Equivalents	0
Short-term investments	0	0
Significant Unobservable Inputs (Level 3) \| U.S. Government Agency Securities and Treasuries
Fair Value Asset Measured On Recurring Basis [Line Items]
Short-term investments	$ 0	$ 0

Available-for-Sale Investments - Summary of Available-for-Sale Securities Held (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 94,052	$ 111,542
Gross unrealized gains	42	5
Gross unrealized losses	(3)	(70)
Fair Value	94,091	111,477
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	90,062	107,571
Gross unrealized gains	42	4
Gross unrealized losses	(3)	(70)
Fair Value	90,101	107,505
U.S. government agency and treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,990
Fair Value	$ 3,990
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		3,971
Gross unrealized gains		1
Fair Value		$ 3,972

Available-for-Sale Investments - Additional Information (Detail) $ in Millions	Mar. 31, 2019 USD ($) Investment Security	Dec. 31, 2018 USD ($) Investment
Investments Debt And Equity Securities [Abstract]
Number of investments in unrealized loss position	19	37
Number of investments in unrealized loss position, more than twelve months	0	0
Aggregate fair value of securities in unrealized loss position \| $	$ 35.6	$ 96.5
Number of securities with other than temporary impairment \| Security	0

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 18,018	$ 17,828
Less accumulated depreciation	(3,670)	(2,987)
Property and equipment, net	14,348	14,841
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	7,287	7,111
Computer and Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	829	781
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	413	413
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	9,484	9,484
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 5	$ 39

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Payroll related	$ 1,165	$ 2,906
Professional fees	544	306
Research and development	2,023	1,585
Other	149	237
Total accrued expenses	$ 3,881	$ 5,034

Common Stock - Additional Information (Detail)	3 Months Ended	136 Months Ended
Common Stock - Additional Information (Detail)	Mar. 31, 2019 Vote	Mar. 31, 2019 USD ($)
Stockholders Equity Note [Abstract]
Number of votes entitled to each share of common stock \| Vote	1
Cash dividends \| $		$ 0

Equity-based Compensation and Equity Incentive Plans - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended
	Jan. 01, 2019	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee unrecognized compensation expense		$ 12,700
Employee unrecognized compensation cost, period of recognition		3 years 1 month 6 days
Equity-based compensation expense		$ 954	$ 919
Restricted Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee unrecognized compensation expense		$ 100
Employee unrecognized compensation cost, period of recognition		1 year 4 months 24 days
Equity-based compensation expense		$ 28	$ 146
Plan 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares available for issuance (in shares)	1,270,073
2015 and 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants		753,164

Equity-based Compensation and Equity Incentive Plans - Schedule of Stock Option Activity Under 2015 and 2017 Plan (Detail) - 2015 and 2017 Plan - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding Beginning balance, Number of options	1,739,884
Granted, Number of options	1,163,980
Forfeited, Number of options	(156,821)
Outstanding Ending balance, Number of options	2,747,043	1,739,884
Number of options, Vested or expected to vest	2,747,043
Number of options, Exercisable	558,274
Beginning balance, Weighted-average price	$ 11.92
Granted, Weighted-average price	8.54
Forfeited, Weighted-average price	13.84
Ending balance, Weighted-average price	10.38	$ 11.92
Weighted-average price Vested or expected to vest	10.38
Weighted-average price, Exercisable	$ 13.10
Outstanding, weighted average remaining contractual term (Year)	9 years 2 months 12 days	9 years
Weighted average remaining contractual term, Vested or expected to vest	9 years 2 months 12 days
Weighted average remaining contractual term, Exercisable	8 years 6 months
Ending balance, Aggregate Intrinsic value	$ 2,030
Aggregate Intrinsic value, Vested or expected to vest at March 31, 2019	$ 2,030

Equity-based Compensation and Equity Incentive Plans - Schedule of Restricted Common Stock Activity (Detail) - Restricted Common Stock	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Beginning balance, Number of unvested shares/units \| shares	118,679
Vested, Number of shares/units \| shares	(18,124)
Forfeited, Number of shares/units \| shares	(12,836)
Ending balance, Number of unvested shares/units \| shares	87,719
Beginning balance, Unvested Grant date fair value \| $ / shares	$ 13.54
Vested, Grant date fair value \| $ / shares	13.53
Forfeited, Grant date fair value \| $ / shares	13.53
Ending balance, Unvested Grant date fair value \| $ / shares	$ 13.55

Equity-based Compensation and Equity Incentive Plans - Schedule of Equity-based Compensation Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 954	$ 919
Research and Development Expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	284	377
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 670	$ 542

Equity-based Compensation and Equity Incentive Plans - Schedule of Equity-based Compensation Expenses by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 954	$ 919
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	926	773
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 28	$ 146

AbbVie Collaboration Agreement - Additional Information (Detail) $ in Thousands			1 Months Ended		3 Months Ended
	Dec. 18, 2018 USD ($)	Sep. 27, 2018 USD ($) Milestone	May 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Feb. 28, 2019 USD ($)	Dec. 31, 2018 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognition of revenue					$ 338	$ 354
Long term deferred revenue					465
Current deferred revenue					1,964			$ 268
AbbVie Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of mile stone payments under second phase \| Milestone		2
Initial milestone payment upon execution of amendment		$ 2,000
Increase in transaction price of performance obligation of second phase	$ 2,000
Remaining milestone achieved							$ 2,500
Recognition of revenue					300	$ 400
Long term deferred revenue					2,000
Current deferred revenue					500
AbbVie Agreement \| IBDCo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront non refundable payment				$ 2,000
Potential milestone payment					$ 16,500
Collaboration in research and development					54 months
Milestone payment			$ 2,000

Net Loss per Share - Schedule of Potentially Common Shares Excluded from Calculation of Net Loss Per share (Detail) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Unvested Restricted Common Stock Awards
Potentially Common Shares Excluded from Calculation of Net Loss Per share	87,719	320,166
Stock Options
Potentially Common Shares Excluded from Calculation of Net Loss Per share	2,747,043	1,741,527

Commitments and Contingencies - Additional Information (Detail)		1 Months Ended	3 Months Ended
	Dec. 07, 2018 USD ($) ft²	Jul. 31, 2017 USD ($) ft²	Mar. 31, 2019 USD ($)
Commitments And Contingencies [Line Items]
Laboratory and office space to be leased \| ft²		41,346
Operating lease annual rent		$ 3,100,000
Term of lease		10 years
Tenant improvement investment		$ 1,600,000
Letter of credit		$ 1,000,000
Renewal term of lease		5 years
Lessee, operating lease, existence of option to extend		true	true
Lessee, operating lease, existence of option to terminate		true
Cash paid included in operating cash flows			$ 800,000
Total right-of-use asset for finance leases			$ 900,000
Master Services Agreement \| Azzur Group, LLC
Commitments And Contingencies [Line Items]
Access and use of space under agreement \| ft²	700
Term of agreement	44 months
Agreement expiration date	Dec. 31, 2022
Term of prior terminate written notice	4 months
Master Services Agreement \| Maximum \| Azzur Group, LLC
Commitments And Contingencies [Line Items]
Estimated project costs	$ 4,800,000

Commitments and Contingencies - Components of Lease Cost for Operating and Finance Leases (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Operating leases
Operating lease cost	$ 694
Variable lease cost	263
Operating and variable lease cost	957
Short-term lease cost	119
Finance leases
Depreciation on finance leases	47
Interest on finance leases	7
Finance lease cost	54
Total lease cost	$ 1,130

Commitments and Contingencies - Summary of Weighted Average Remaining Lease Term and Weighted Average Discount Rate for Operating and Finance Leases (Detail)	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Operating Lease, Weighted average discount rate	9.00%
Operating Lease, Weighted average remaining lease term (years)	9 years 4 months 24 days
Finance Leases, Weighted average discount rate	5.90%
Finance Leases, Weighted average remaining lease term (years)	1 year 6 months

Commitments and Contingencies - Summary of Maturity of Lease Liabilities for Operating and Finance Leases (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Lease
2019	$ 2,390
2020	3,270
2021	3,369
2022	3,470
2023	3,574
Thereafter	18,067
Total lease payments	34,140
Less: imputed interest	10,449
Total lease liabilities	23,691	$ 24,000
Current lease liabilities	1,374
Long-term lease liabilities	22,317
Finance Leases
2019	215
2020	214
2021	2
Total lease payments	431
Less: imputed interest	21
Total lease liabilities	410
Current lease liabilities	269		$ 266
Long-term lease liabilities	$ 141		$ 210

Commitments and Contingencies - Schedule of Aggregate Future Lease Payments for Operating and Capital Leases (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Operating lease
2019	$ 3,175
2020	3,270
2021	3,369
2022	3,470
2023	3,574
Thereafter	18,067
Total future minimum lease payments	34,925
Capital leases
2019	287
2020	214
2021	2
Total future minimum lease payments	503
Less amounts representing interest	27
Capital lease obligations at December 31, 2018	476
Less current portion of capital lease obligations	266
Capital lease obligations, net of current portion	$ 210