Assembly Biosciences (ASMB) 10-Q 7 Nov 19 2019 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 04, 2019
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2019
Entity File Number	001-35005
Entity Registrant Name	ASSEMBLY BIOSCIENCES, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-8729264
Entity Address, Address Line One	11711 N. Meridian St.
Entity Address, Address Line Two	Suite 310
Entity Address, City or Town	Carmel
Entity Address, State or Province	IN
Entity Address, Postal Zip Code	46032
City Area Code	833
Local Phone Number	509-4583
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001426800
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Trading Symbol	ASMB
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, par value $0.001
Entity Common Stock, Shares Outstanding		26,047,046
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 24,867	$ 41,471
Marketable securities	132,070	176,609
Accounts receivable from collaboration	2,944	2,430
Prepaid expenses and other current assets	5,441	1,992
Total current assets	165,322	222,502
Property and equipment, net	1,931	557
Operating lease right-of-use assets	12,783	0
Other assets	1,671	3,348
Indefinite-lived intangible asset	29,000	29,000
Goodwill	12,638	12,638
Total assets	223,345	268,045
Current liabilities
Accounts payable	2,709	3,693
Accrued expenses	9,430	9,679
Deferred revenue - short-term	6,151	5,100
Operating lease liabilities - short-term	3,208	0
Total current liabilities	21,498	18,472
Deferred rent	0	108
Deferred tax liabilities	3,251	3,252
Deferred revenue - long-term	32,268	35,560
Operating lease liabilities - long-term	9,839	0
Total liabilities	66,856	57,392
Commitments and contingencies
Stockholders' equity
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 100,000,000 shares authorized as of September 30, 2019 and December 31, 2018; 25,872,723 and 25,495,425 shares issued and outstanding as of September 30, 2019 and December 31, 2018, respectively	26	25
Additional paid-in capital	569,005	552,762
Accumulated other comprehensive loss	(205)	(347)
Accumulated deficit	(412,337)	(341,787)
Total stockholders' equity	156,489	210,653
Total liabilities and stockholders' equity	$ 223,345	$ 268,045

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 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, shares authorized	100,000,000	100,000,000
Common stock, shares issued	25,872,723	25,495,425
Common stock, shares outstanding	25,872,723	25,495,425

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Collaboration revenue	$ 4,231	$ 4,286	$ 11,197	$ 11,069
Operating expenses:
Research and development	21,736	19,109	63,141	51,490
General and administrative	8,488	7,752	22,085	25,992
Total operating expenses	30,224	26,861	85,226	77,482
Loss from operations	(25,993)	(22,575)	(74,029)	(66,413)
Other income (expenses)
Interest and other income	983	1,116	3,441	2,015
Other income (expense), net		(82)	5	(232)
Total other income	983	1,034	3,446	1,783
Loss before income taxes	(25,010)	(21,541)	(70,583)	(64,630)
Income tax benefit	15	6	33	40
Net loss	(24,995)	(21,535)	(70,550)	(64,590)
Other comprehensive (loss) income
Unrealized gain (loss) on marketable securities, net of tax	(18)	17	142	37
Comprehensive loss	$ (25,013)	$ (21,518)	$ (70,408)	$ (64,553)
Net loss per share, basic and diluted	$ (0.96)	$ (0.87)	$ (2.74)	$ (2.95)
Weighted average common shares outstanding, basic and diluted	25,912,568	24,878,413	25,765,414	21,900,943

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (70,550)	$ (64,590)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	377	473
Stock-based compensation	14,049	21,678
Net accretion and amortization of investments in marketable securities	(1,503)	232
Non-cash rent expense	3,344	0
Deferred income tax benefit	(10)	(40)
Loss on disposal of fixed assets	102	0
Other	(5)	0
Changes in operating assets and liabilities:
Accounts receivable from collaboration	(514)	(316)
Prepaid expenses and other current assets	(3,763)	(2,445)
Other assets	1,677	(611)
Accounts payable	(984)	863
Accrued expenses	(330)	378
Deferred revenue	(2,241)	(3,861)
Deferred rent	0	8
Operating lease liabilities	(3,188)	0
Net cash used in operating activities	(63,539)	(48,231)
Cash flows from investing activities
Purchases of property and equipment	(1,539)	(129)
Purchases of marketable securities	(149,327)	(115,030)
Proceeds from maturities of marketable securities	166,911	41,921
Proceeds from sale of marketable securities	28,659	0
Net cash provided by (used in) investing activities	44,704	(73,238)
Cash flows from financing activities
Proceeds from common stock sold, net of underwriters' discount and cost	0	155,425
Net proceeds from the issuance of common stock through equity plans	2,231	3,763
Net cash provided by financing activities	2,231	159,188
Net increase (decrease) in cash and cash equivalents	(16,604)	37,719
Cash and cash equivalents at the beginning of the period	41,471	82,033
Cash and cash equivalents at the end of the period	$ 24,867	$ 119,752

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance at Dec. 31, 2017	$ 113,120	$ 20	$ 364,528	$ (392)	$ (251,036)
Balance (in shares) at Dec. 31, 2017		20,137,974
Proceeds from common stock sold, net of underwriters' discount and cost	155,425	$ 4	155,421
Proceeds from common stock sold, net of underwriters' discount and cost (in shares)		4,600,000
Issuance of common stock upon exercise of stock options	3,763	$ 1	3,762
Issuance of common stock upon exercise of stock options ( in shares )		721,210
Issuance of shares of common stock for settlement of restricted stock units (RSUs)(in shares)		938
Unrealized gain (loss) on marketable securities, net of tax	37			37
Stock-based compensation	21,678		21,678
Net loss	(64,590)				(64,590)
Balance at Sep. 30, 2018	229,433	$ 25	545,389	(355)	(315,626)
Balance (in shares) at Sep. 30, 2018		25,460,122
Balance at Jun. 30, 2018	89,101	$ 21	383,543	(372)	(294,091)
Balance (in shares) at Jun. 30, 2018		20,614,498
Proceeds from common stock sold, net of underwriters' discount and cost	155,425	$ 4	155,421
Proceeds from common stock sold, net of underwriters' discount and cost (in shares)		4,600,000
Issuance of common stock upon exercise of stock options	419		419
Issuance of common stock upon exercise of stock options ( in shares )		244,686
Issuance of shares of common stock for settlement of restricted stock units (RSUs)(in shares)		938
Unrealized gain (loss) on marketable securities, net of tax	17			17
Stock-based compensation	6,006		6,006
Net loss	(21,535)				(21,535)
Balance at Sep. 30, 2018	229,433	$ 25	545,389	(355)	(315,626)
Balance (in shares) at Sep. 30, 2018		25,460,122
Balance at Dec. 31, 2018	210,653	$ 25	552,762	(347)	(341,787)
Balance (in shares) at Dec. 31, 2018		25,495,425
Issuance of common stock upon exercise of stock options	1,716		1,716
Issuance of common stock upon exercise of stock options ( in shares )		243,481
Issuance of common stock under Employee Stock Purchase Plan (ESPP)	515		515
Issuance of common stock under Employee Stock Purchase Plan (ESPP) (in shares)		36,804
Issuance of shares of common stock for settlement of restricted stock units (RSUs)		$ 1	(1)
Issuance of shares of common stock for settlement of restricted stock units (RSUs)(in shares)		97,013
Reclassification of stock-based awards from equity to accrued expenses	(4)		(4)
Unrealized gain (loss) on marketable securities, net of tax	142			142
Stock-based compensation	14,017		14,017
Net loss	(70,550)				(70,550)
Balance at Sep. 30, 2019	156,489	$ 26	569,005	(205)	(412,337)
Balance (in shares) at Sep. 30, 2019		25,872,723
Balance at Jun. 30, 2019	174,707	$ 26	562,210	(187)	(387,342)
Balance (in shares) at Jun. 30, 2019		25,646,783
Issuance of common stock upon exercise of stock options	1,385		1,385
Issuance of common stock upon exercise of stock options ( in shares )		192,606
Issuance of shares of common stock for settlement of restricted stock units (RSUs)(in shares)		33,334
Unrealized gain (loss) on marketable securities, net of tax	(18)			(18)
Stock-based compensation	5,410		5,410
Net loss	(24,995)				(24,995)
Balance at Sep. 30, 2019	$ 156,489	$ 26	$ 569,005	$ (205)	$ (412,337)
Balance (in shares) at Sep. 30, 2019		25,872,723

Nature of Business

Nature of Business	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	Note 1 - Nature of Business Overview Assembly Biosciences, Inc., together with its subsidiaries (Assembly or the Company), incorporated in Delaware in October 2005, is a clinical-stage biotechnology company developing innovative therapeutics targeting chronic hepatitis B virus (HBV) and diseases associated with the microbiome. The Company operates in one segment and is headquartered in Carmel, Indiana with operations in South San Francisco, California and Groton, Connecticut. The Company’s HBV-cure program is pursuing multiple drug candidates that inhibit the HBV lifecycle and block the generation of covalently closed circular DNA (cccDNA), with the aim of increasing the current low cure rates for patients with HBV. Assembly has discovered several novel core inhibitors, which are small molecules that directly target and allosterically modify the HBV core (HBc) protein. The Company’s Microbiome program consists of a fully integrated platform that includes a strain isolation, identification, characterization and function-based selection process, methods for strain purification and growth under conditions compliant with current Good Manufacturing Practice (cGMP) requirements, and a licensed patented delivery system, GEMICEL®, which is designed to allow for targeted oral delivery of live biologic and conventional therapies to the lower gastrointestinal (GI) tract. Using the Company’s microbiome platform capabilities, the Company is exploring product candidates for multiple disease indications, including ulcerative colitis (UC), Crohn’s disease and irritable bowel syndrome (IBS) with Allergan Pharmaceuticals International Limited (Allergan) in connection with its Research, Development, Collaboration and License Agreement (the Collaboration Agreement), as well as immune-mediated and metabolic disorders and oncology, which indications the Company will pursue either internally or in collaboration with other parties. Liquidity The Company has not derived any revenue from product sales to date and currently has no approved products. Once a product has been developed, it will need to be approved for sale by the U.S. Food and Drug Administration (FDA) or an applicable foreign regulatory agency. Since inception, the Company’s operations have been financed primarily through the sale of equity securities, the proceeds from the exercise of warrants and stock options, the issuance of debt and an upfront payment related to the Collaboration Agreement. The Company has incurred losses from operations since inception and expects to continue to incur substantial losses for the next several years as it continues its product development efforts. Management believes the Company currently has sufficient funds to meet its operating requirements for at least the next twelve months following the date that these unaudited condensed consolidated interim financial statements are issued. If the Company cannot generate significant cash from its operations, it intends to obtain any additional funding it requires through strategic relationships, public or private equity or debt financings, grants or other arrangements. The Company cannot assure such funding will be available on reasonable terms, if at all. If the Company is unable to generate enough revenue from the Collaboration Agreement when needed or to secure additional sources of funding and receive related full and timely collections of amounts due, it may be necessary to significantly reduce the current rate of spending through reductions in staff and delaying, scaling back, or stopping certain research and development programs, including more costly clinical trials.

Summary of Significant Accounti

Summary of Significant Accounting Policies and Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Recent Accounting Pronouncements	Note 2 - Summary of Significant Accounting Policies and Recent Accounting Pronouncements Basis of Presentation The accompanying unaudited interim condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and pursuant to the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the U.S. Securities and Exchange Commission (SEC). In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements and include normal recurring adjustments necessary for the fair presentation of the Company’s financial position and its results of operations and comprehensive loss and its cash flows for the periods presented. These statements do not include all disclosures required by U.S. GAAP and should be read in conjunction with the Company’s audited consolidated financial statements and accompanying notes for the fiscal year ended December 31, 2018, which are contained in the Company’s Annual Report on Form 10-K as filed with the SEC on February 28, 2019. The results for the three and nine months ended September 30, 2019 are not necessarily indicative of results to be expected for the entire year ending December 31, 2019 or future operating periods. Use of Estimates The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Significant estimates inherent in the preparation of the accompanying unaudited condensed consolidated financial statements include revenue recognition, clinical trial accruals, recoverability and useful lives (indefinite or finite) of intangible assets, assessment of impairment of goodwill, provisions for income taxes, amounts receivable and recognized as revenue under the Collaboration Agreement, measurement of operating lease liabilities, and the fair value of stock options, stock appreciation rights, and restricted stock units (RSUs) granted to employees, directors and consultants. The Company’s estimates could be affected by external conditions, including those unique to the Company and general economic conditions. It is reasonably possible that these external factors could have an effect on the Company’s estimates and could cause actual results to differ from those estimates and assumptions. Significant Accounting Policies There have been no material changes to the Company’s significant accounting policies from those described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, other than as set forth below. Stock-Based Compensation The Company expenses stock-based compensation to employees and Board members over the requisite service period based on the estimated grant-date fair value of the awards. Stock-based awards with graded-vesting schedules are recognized using the accelerated attribution method over the requisite service period for each separately vesting portion of the award. Prior to the adoption of Accounting Standards Update (ASU) 2018-07 (ASU 2018-07) on January 1, 2019, the Company remeasured the fair value of the non-employee awards at each reporting period prior to vesting and finally at the vesting date of the award. Changes in the estimated fair value of these non-employee awards were recognized as compensation expense in the period of change. Subsequent to the adoption of ASU 2018-07, the Company recognizes non-employee compensation costs over the requisite service period based on a measurement of fair value for each stock award. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model and the assumptions used in calculating the fair value of stock-based awards represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment. Forfeitures are recognized when incurred. The fair value of restricted stock units is determined based on the number of shares granted and the quoted market price of the Company’s common stock on the date of grant. The fair value of restricted stock units with performance conditions deemed probable of being achieved and vesting are amortized to expense over the requisite service period using the accelerated attribution method of expense recognition. Leases All of the Company’s leases are operating leases for facilities and equipment. Prior to January 1, 2019, the Company recognized related rent expense on a straight-line basis over the term of the lease. Incentives granted under the Company’s facilities lease, including allowances for leasehold improvements and rent holidays, were recognized as reductions to rental expense on a straight-line basis over the term of the lease. Deferred rent consisted of the difference between cash payments and the rent expense recognized. Subsequent to the adoption of the new leasing standard on January 1, 2019, the Company recognizes a lease asset for its right to use the underlying asset and a lease liability for the corresponding lease obligation. The Company determines whether an arrangement is or contains a lease at contract inception. Operating leases are included in operating lease right-of-use assets, operating lease liabilities - short-term, and operating lease liabilities - long-term in the Company’s condensed consolidated balance sheet at September 30, 2019. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the net present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. The incremental borrowing rate represents the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably assured the Company will exercise the option to extend the contract. Periods covered by an option to extend are included in the lease term if the lessor controls the exercise of that option. The operating lease right-of-use assets also include any lease payments made and exclude lease incentives. Lease expense is recognized on a straight-line basis over the expected lease term. Variable lease expenses are recorded when incurred. The Company has elected not to separate lease and non-lease components for its leased assets and accounts for all lease and non-lease components of its agreements as a single lease component. Net Loss per Share Basic net loss per common share excludes dilution and is computed by dividing net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per common share reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the entity unless inclusion of such shares would be anti-dilutive. Since the Company has only incurred losses, basic and diluted net loss per share is the same. Securities that could potentially dilute loss per share in the future that were not included in the computation of diluted loss per share are as follows: Nine Months Ended September 30, 2019 2018 Warrants to purchase common stock 15,296 15,296 Options to purchase common stock 5,462,773 4,422,194 Common stock subject to purchase under ESPP 17,018 10,198 Unvested RSUs 668,515 343,465 Total 6,163,602 4,791,153 A reconciliation of the numerators and the denominators of the basic and diluted net loss per common share computations is as follows (in thousands, except per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net loss (in thousands) (24,995 ) (21,535 ) (70,550 ) (64,590 ) Denominator: Weighted average common shares outstanding for diluted net (loss) income per share 25,912,568 24,878,413 25,765,414 21,900,943 Net (loss) income per share: Basic (0.96 ) (0.87 ) (2.74 ) (2.95 ) Diluted (0.96 ) (0.87 ) (2.74 ) (2.95 ) Adoption of Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, Leases The Company adopted ASU 2016-02 on January 1, 2019 using the modified retrospective approach and elected the package of practical expedients permitted under transition guidance, which allowed the Company to carry forward its historical assessments of: (1) whether contracts are or contain leases, (2) lease classification and (3) initial direct costs. The Company did not elect the use-of-hindsight practical expedient, which would require the Company to reassess the lease term of its leases based on all facts and circumstances through the effective date, and the Company did not elect the practical expedient pertaining to land easements as this is not applicable to the Company’s current contract portfolio. The Company elected the post-transition practical expedient to not separate lease components from nonlease components for all existing lease classes. The Company also elected a policy of not recording leases on its condensed consolidated balance sheets when the leases have a term of 12 months or less and the Company is not reasonably certain to elect an option to purchase the leased asset. The adoption of this standard resulted in the recognition of right of use (ROU) assets and lease liabilities of $13.8 million and $14.0 million, respectively, and the derecognition of the deferred rent balance of $0.1 million as of January 1, 2019. The adoption of the standard had no impact on the Company’s condensed consolidated statements of operations and comprehensive loss or to its cash flows from or used in operating, financing, or investing activities on its condensed consolidated statements of cash flows. No cumulative-effect adjustment within accumulated deficit was required to be recorded as a result of adopting this standard. On January 1, 2019, the Company adopted ASU 2018-02, Income Statement - Reporting Comprehensive Income, (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, On January 1, 2019, the Company adopted ASU 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting Compensation – Stock Compensation In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification Recent Accounting Pronouncements In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement, In January 2017, the FASB issued ASU 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04), which simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. Under the amendments in ASU 2017-04, an entity should recognize an impairment charge for the amount by which the carrying amount of a reporting unit exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The updated guidance requires a prospective adoption. ASU 2017-04 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. The Company is currently evaluating the timing and impact of adopting this new accounting standard on its condensed consolidated financial statements and related disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326 Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments Financial Instruments - Credit Losses (Topic 326): Targeted Transition Relief

Investments in Marketable Secur

Investments in Marketable Securities	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Investments in Marketable Securities	Note 3 – Investments in Marketable Securities The carrying amounts of cash equivalents and marketable securities approximate their fair value based upon quoted market prices. Certain of the Company’s financial instruments are not measured at fair value on a recurring basis, but are recorded at amounts that approximate their fair value due to their liquid or short-term nature, such as cash, accounts receivable, accounts payable, accrued expenses, lease liability-short term and deferred revenue-short term. The Company uses the following three-level hierarchy that maximizes the use of observable inputs and minimizes the use of unobservable inputs to value its financial instruments: Level 1: Observable inputs such as unadjusted quoted prices in active markets for identical instruments. Level 2: Quoted prices for similar instruments that are directly or indirectly observable in the marketplace. Level 3: Significant unobservable inputs that are supported by little or no market activity and that are financial instruments whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant judgment or estimation. Investments in marketable securities consisted of the following: September 30, 2019 ($ in thousands) Amortized Cost Gross Unrealized Gain (1) Gross Unrealized Loss (1) Fair Value Short-term available-for-sale securities U.S. and foreign corporate debt securities $ 34,111 $ 44 $ — $ 34,155 Asset-backed securities 22,117 16 — 22,133 U.S. treasury securities 27,008 16 (6 ) 27,018 U.S. and foreign commercial paper 48,764 — — 48,764 Total $ 132,000 $ 76 $ (6 ) $ 132,070 (1) Gross unrealized gain (loss) is pre-tax. December 31, 2018 ($ in thousands) Amortized Cost Gross Unrealized Gain (1) Gross Unrealized Loss (1) Fair Value Short-term available-for-sale securities U.S. and foreign corporate debt securities $ 73,251 $ — $ (92 ) $ 73,159 Asset-backed securities 28,450 — (31 ) 28,419 U.S. treasury securities 19,898 — (3 ) 19,895 U.S. and foreign commercial paper 55,136 — — 55,136 Total $ 176,735 $ — $ (126 ) $ 176,609 (1) Gross unrealized gain (loss) is pre-tax. The contractual term to maturity of short-term marketable securities held by the Company as of September 30, 2019 is less than one year. There were no long-term marketable securities held by the Company as of September 30, 2019. Realized gains and losses for the three and nine months ended September 30, 2019 and 2018 were not significant. The following tables present the fair value of the Company’s financial assets measured at fair value on a recurring basis: September 30, 2019 ($ in thousands) Level 1 Level 2 Level 3 Fair Value Cash equivalents Money market fund $ 19,948 $ — $ — $ 19,948 Total cash equivalents 19,948 — — 19,948 Short-term investments U.S. and foreign corporate debt securities — 34,155 — 34,155 Asset-backed securities — 22,133 — 22,133 U.S. treasury securities — 27,018 — 27,018 U.S. and foreign commercial paper — 48,764 — 48,764 Total short-term investments — 132,070 — 132,070 Total assets measured at fair value $ 19,948 $ 132,070 $ — $ 152,018 December 31, 2018 ($ in thousands) Level 1 Level 2 Level 3 Fair Value Cash equivalents Money market fund $ 39,345 $ — $ — $ 39,345 Total cash equivalents 39,345 — — 39,345 Short-term investments U.S. and foreign corporate debt securities — 73,159 — 73,159 Asset-backed securities — 28,419 — 28,419 U.S. treasury securities — 19,895 — 19,895 U.S. and foreign commercial paper — 55,136 — 55,136 Total short-term investments — 176,609 — 176,609 Total assets measured at fair value $ 39,345 $ 176,609 $ — $ 215,954 The Company estimates the fair value of its U.S. and foreign corporate debt securities, asset-backed securities, U.S. treasury securities and U.S. and foreign commercial paper by taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data, and other observable inputs. There were no transfers between Level 1, Level 2 or Level 3 during the periods presented.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Property and Equipment, Net	Note 4 - Property and Equipment, net Property and equipment consist of the following: Useful life September 30, December 31, ($ in thousands) (Years) 2019 2018 Computer hardware and software 3 $ — $ 194 Lab equipment 3 to 5 230 407 Office equipment 7 699 70 Leasehold improvement 1 to 5 2,084 790 Total property, plant and equipment 3,013 1,461 Less: Accumulated depreciation and amortization (1,082 ) (1,057 ) Construction in progress N/A — 153 Property, plant and equipment, net $ 1,931 $ 557 Depreciation expense was approximately $0.1 million and $0.4 million for the three and nine months ended September 30, 2019, respectively and approximately $0.2 million and $0.5 million for the three and nine months ended September 30, 2018, respectively, and was recorded in both research and development expense and general and administrative expense in the unaudited condensed consolidated statements of operations and comprehensive loss.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Accrued Expenses	Note 5 – Accrued Expenses Accrued expenses consist of the following: September 30, December 31, ($ in thousands) 2019 2018 Accrued expenses: Accrued compensation $ 4,042 $ 5,011 Accrued clinical trial expenses 4,321 3,561 Accrued professional fees and other 1,067 1,107 Total accrued expenses $ 9,430 $ 9,679

Stock Plans and Stock-Based Com

Stock Plans and Stock-Based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Plans and Stock-Based Compensation	Note 6 – Stock Plans and Stock-Based Compensation Equity Incentive Plans In May 2018, the Company’s stockholders approved the Assembly Biosciences, Inc. 2018 Stock Incentive Plan (the 2018 Plan) pursuant to which the Company reserved 1,900,000 shares of its common stock for issuance in connection with equity incentive awards, and in May 2019, the Company’s stockholders approved Amendment No. 1 (the Amendment) to the 2018 Plan to increase the number of shares reserved for issuance thereunder from 1,900,000 shares of common stock to 3,000,000. In May 2018, the Company’s stockholders also approved the Assembly Biosciences, Inc. Employee Stock Purchase Plan (the 2018 ESPP), pursuant to which eligible employees can purchase an aggregate of up to 400,000 shares of the Company’s common stock at the end of predetermined offering periods at 85% of the lower of the fair market value at the beginning or end of the offering period. As of September 30, 2019, the Company had awards outstanding under the following shareholder-approved plans: ● 2010 Equity Incentive Plan (the 2010 Plan), which has been frozen; ● the Amended and Restated 2014 Stock Incentive Plan (the 2014 Plan); and ● the 2018 Plan. Shares of common stock underlying awards that are forfeited under the 2010 Plan on or after June 2, 2016 will become available for issuance under the 2014 Plan. As of September 30, 2019, the Company also had awards outstanding under the Assembly Biosciences, Inc. 2017 Inducement Award Plan (the 2017 Plan) and the Assembly Biosciences, Inc. 2019 Inducement Award Plan (the 2019 Plan). The Company issues new shares of common stock to settle options exercised and upon settlement of vested RSUs. The Company also issues new shares of common stock in connection with purchases of shares of common stock by eligible employees under the Company’s 2018 ESPP. Stock Plan Activity Stock Options A summary of the Company’s option activity and related information for the nine months ended September 30, 2019 is as follows: Number of Shares Weighted Average Exercise Price Per Share Total Intrinsic Value (in thousands) Outstanding as of December 31, 2018 4,637,145 $ 17.21 $ 48,179 Granted 1,418,350 15.74 — Exercised (243,481 ) 7.05 1,642 Forfeited (346,741 ) 44.85 117 Expired (2,500 ) 49.14 — Outstanding as of September 30, 2019 5,462,773 $ 15.52 $ 9,000 Options vested and exercisable 3,278,755 $ 12.01 $ 8,656 Restricted Stock Units (RSUs) A summary of the Company’s RSUs and related information for the nine months ended September 30, 2019 is as follows: Number of RSU's Weighted Average Grant Price Outstanding as of December 31, 2018 568,005 $ 37.18 Granted 435,928 15.24 Vested and settled (97,254 ) 45.05 Forfeited (126,497 ) 24.41 Outstanding as of September 30, 2019 780,182 (1) $ 26.01 (1) Includes 111,667 RSUs that have vested but are subject to deferred settlement. As of September 30, 2019, RSUs outstanding include 45,000 RSUs granted in December 2017 and 100,000 RSUs granted in September 2019, each with performance-based conditions to executives of the Company. In the second quarter of 2019, 100,000 RSUs granted to a former officer were forfeited due to his departure. These RSUs had a grant date fair value of $2.4 million and were vesting over time but would have accelerated upon the achievement of certain performance-based conditions. The Company reversed the previously recognized expense of $0.4 million related to these forfeited awards upon the departure of the former officer. As of September 30, 2019, the Company had unrecognized stock-based compensation expense related to all unvested RSUs of $10.2 million. In May 2019, employees purchased 36,804 shares of common stock under the 2018 ESPP. Valuation Assumptions The fair value of the stock options granted or modified during the periods indicated was estimated using the Black-Scholes option pricing model, based on the following assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Exercise price $10.91 - $49.14 $38.88 - $41.25 $10.91 - $49.14 $38.88 - $57.53 Expected volatility 66.4% - 80.6% 76.0% - 84.5% 66.4% - 83.2% 76.0% - 86.1% Risk-free rate 1.36% - 1.89% 2.75% - 2.94% 1.36% - 2.65% 2.56% - 2.94% Expected term (years) 5.5 - 9.6 5.5 - 7.0 5.5 - 9.6 5.5 - 7.0 Dividend yield 0% 0% 0% 0% The fair value of RSUs granted is determined based on the price of the Company’s common stock on the date of grant. Stock-Based Compensation Expense The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss: Three Months Ended September 30, Nine Months Ended September 30, ($ in thousands) 2019 2018 2019 2018 Research and development $ 2,464 $ 2,474 $ 8,309 $ 8,687 General and administrative 2,940 3,532 5,740 (1) 12,991 Total stock-based compensation expense $ 5,404 $ 6,006 $ 14,049 $ 21,678 (1) Includes the reversal of previously recognized expense of $3.6 million related to forfeited awards resulting from the departure of one of our former officers during the period.

Collaboration Agreement

Collaboration Agreement	9 Months Ended
	Sep. 30, 2019
Collaboration Agreement [Abstract]
Collaboration Agreement	Note 7 - Collaboration Agreement Allergan In January 2017, the Company entered into the Collaboration Agreement with Allergan to develop and commercialize select microbiome gastrointestinal disease therapies. Pursuant to the Collaboration Agreement, the Company granted Allergan an exclusive worldwide license to certain of its intellectual property, including its intellectual property arising under the Collaboration Agreement, to develop and commercialize licensed compounds for UC, Crohn’s disease, and two compounds for IBS. Allergan and the Company also agreed to collaborate on research and development activities with respect to the licensed compounds in accordance with a mutually agreed upon research and development plan. Per the terms of the Collaboration Agreement, Allergan can select backups and additional target indications to add to the licenses granted for additional consideration and also has the ability to enter into a contract manufacturing agreement with the Company for compound supply at cost plus an agreed upon margin. In addition, the Company will participate on a Joint Development Committee (JDC) and Joint Patent Committee (JPC). The Company provided to Allergan standard indemnification and protection of licensed intellectual property, which is part of assurance that the license meets the contract’s specifications and is not an obligation to provide goods or services. Allergan paid the Company an upfront non-refundable payment of $50.0 million, which was received in 2017. Additionally, the Company is eligible to receive variable consideration in the form of research and development cost reimbursements, up to approximately $631.0 million related to seven development milestones and up to approximately $2.14 billion related to 12 commercial development and sales milestones in connection with the successful development and commercialization of licensed compounds. In addition, the Company is eligible to receive tiered royalties at rates ranging from the mid-single digits to the mid-teens based on net sales. Allergan and the Company have agreed to share research and development costs up to an aggregate of $75.0 million through proof-of-concept (POC) studies on a ⅔, ⅓ basis, respectively, and Allergan has agreed to assume all post-POC development costs. In the event any pre-POC development costs exceed $75.0 million in the aggregate, the Company may elect either (a) to fund ⅓ of such costs in excess of $75.0 million or (b) to allow Allergan to deduct from future development milestone payments ⅓ of the development costs funded by Allergan in excess of $75.0 million plus a premium of 25%. The Company has an option to co-promote the licensed programs in the U.S. and China, subject to certain conditions set forth in the Collaboration Agreement. Allergan may terminate the Collaboration Agreement at any time upon 120 days’ advance written notice to the Company. Unless terminated early, the Collaboration Agreement has a term that ends on the earlier of the (i) the period when POC studies have been completed and no further licensed compounds or licensed products are in development, and (ii) expiration of the last to exist valid claim covering the manufacture, use and sale of the licensed products. The Collaboration Agreement also contains customary provisions for termination by either party, including in the event of breach of the Collaboration Agreement, subject to cure. Upon termination for convenience, the licenses granted by the Company and its know-how all revert to the Company. The Company concluded that Allergan is a customer and that the Collaboration Agreement is not subject to accounting literature on collaborative arrangements. This is because the Company granted to Allergan licenses to its intellectual property and research and development services, all of which are outputs of the Company’s ongoing activities, in exchange for consideration. The Company identified the following material promises under the Collaboration Agreement: (1) transfer of licenses to intellectual property for the four initial indications, inclusive of the related technology know-how (Licenses) and (2) the obligation to perform research development services through POC (Development Services). The Company’s participation on the JDC and JPC were considered to be immaterial in the context of the contract. The Company’s co-promotion option was not considered to be a performance obligation. Allergan’s selection of backups or additional target indications to add to the licenses granted for additional consideration and ability to enter into a contract manufacturing agreement with the Company for compound supply at cost plus an agreed upon margin were not considered to be performance obligations as the Company concluded the options were not offered at a discount that exceeds discounts available to other customers, and therefore were not material rights. The grant of additional licensing rights upon option exercises and contract manufacturing agreements will be accounted for as separate contracts when they occur. The Company concluded the Licenses each were considered to be functional as they have significant standalone functionality and were capable of being distinct. However, the Company determined that each of the Licenses individually were not distinct from the Development Services within the context of the agreement. This is because Allergan is dependent on the Company to execute the Development Services, which it is uniquely able to perform, in order for Allergan to benefit from the Licenses. As such, the Company determined that it has four performance obligations under the Collaboration Agreement associated with the transfer of the four compound Licenses combined with the performance of the Development Services for each of the four compound indications. The Company determined that the four performance obligations will be performed over the duration of the contract, which began in February 2017 and ends upon completion of the Development Services. The Company originally estimated the completion of the Development Services to be in 2024. During the second quarter of 2019, the completion of the Development Services was extended to 2025 based on updated estimates of effort associated with the Company’s and Allergan’s development plans. This change in estimate did not have a material impact on the Company’s revenue recognition. The Company is using a cost-based input method to measure proportional performance and to calculate the corresponding amount of revenue to recognize. The Company believes this is the best measure of progress because other measures do not reflect how the Company transfers its performance obligation to Allergan. In applying the cost-based input method of revenue recognition, the Company measures costs incurred relative to budgeted costs to fulfill the four performance obligations. These costs consist primarily of third-party contract costs and internal labor costs. Revenue will be recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligations. To allocate transaction price among the four performance obligations, the Company estimated their standalone selling price (SSP) using an income-based valuation approach for the estimated value a licensor of the compounds would receive considering the stage of the compounds’ development. The Company believes that a change in the assumptions used to determine its best estimate of selling price for the four performance obligations would not have a significant effect on the allocation of consideration received to the four performance obligations. The transaction price at the inception of the agreement and upon adoption of ASC 606 was limited to $50.0 million upfront payment. Of this amount, the Company allocated $12.5 million to each of the four performance obligations. Research and development cost reimbursement payments are included in the transaction price in the reporting period that the Company concludes that it is probable that recording revenue in the period will not result in a significant reversal in amounts recognized in future periods. The variable consideration related to the remaining development and commercialization milestone payments has not been included in the transaction price as these were fully constrained at September 30, 2019. As part of the Company’s evaluation of the development and commercialization milestones constraint, the Company determined that the achievement of such milestones is contingent upon success in future clinical trials and regulatory approvals which are not within its control and uncertain at this stage. Any variable consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as they were determined to relate predominantly to the license granted to Allergan. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The Company did not incur any significant incremental costs of obtaining the Allergan contract. For the nine months ended September 30, 2019 and 2018, the Company recognized approximately $11.2 million and $11.1 million, respectively, in revenue associated with the Collaboration Agreement. Short-term and long-term deferred revenue contract liabilities related to the Collaboration Agreement were approximately $6.2 million and approximately $32.3 million at September 30, 2019 and approximately $5.1 million and approximately $35.6 million at December 31, 2018. On the unaudited condensed consolidated balance sheets, contract asset balances of approximately $2.9 million and approximately $2.4 million were recorded as accounts receivable from collaboration as of September 30, 2019 and December 31, 2018, respectively. The following table presents changes in the Company’s contract liabilities ($ in thousands): Balance at Beginning of Period Additions Deductions Balance at End of Period Nine Months Ended September 30, 2019 Contract liabilities: Deferred revenue $ 40,660 $ — $ (2,241 ) $ 38,419 Balance at Beginning of Period Additions Deductions Balance at End of Period Nine Months Ended September 30, 2018 Contract liabilities: Deferred revenue $ 45,785 $ — $ (3,861 ) $ 41,924 Three Months Ended September 30, Nine Months Ended September 30, ($ in thousands) 2019 2018 2019 2018 Collaboration revenue recognized in the period from Amounts included in deferred revenue at the beginning of the period 1,245 1,666 2,241 3,861 Performance obligations satisfied in previous period — — — —

Milestones and Research Agreeme

Milestones and Research Agreements	9 Months Ended
	Sep. 30, 2019
Milestones And Research Agreements [Abstract]
Milestones and Research Agreements	Note 8 - Milestones and Research Agreements HBV Research Agreement with Indiana University Since September 2013, the Company has been party to an exclusive License Agreement dated September 3, 2013 with Indiana University Research and Technology Corporation (IURTC) from whom it has licensed aspects of the Company’s HBV program held by IURTC. The license agreement requires the Company to make milestone payments based upon the successful accomplishment of clinical and regulatory milestones. The aggregate amount of all performance milestone payments under the IURTC license agreement, should all milestones through development be met, is approximately $0.8 million, with a portion related to the first performance milestone having been paid. The Company also is obligated to pay IURTC royalty payments based on net sales of the licensed technology. The Company is also obligated to pay diligence maintenance fees each year to the extent that the royalty, sublicensing, and milestone payments to IURTC are less than the diligence maintenance fee for that year. Amounts paid in the nine months ended September 30, 2019 and 2018 were insignificant. Microbiome Targeted Colonic Delivery Platform In November 2013, the Company entered into a License and Collaboration Agreement with Therabiome, LLC (Therabiome), for all intellectual property and know-how owned or controlled by Therabiome relating to the oral delivery of pharmaceutical drugs to specific sites in the intestine, using a pH sensitive controlled release capsule-in-capsule technology. The Company will be solely responsible for all research and development activities with respect to any product it develops under the license. The Company must pay Therabiome clinical and regulatory milestones for each product or therapy advanced from the platform for U.S. regulatory milestones. The Company also must pay Therabiome lesser amounts for foreign regulatory milestones, which vary by country and region. The Company also must pay Therabiome royalties on annual net sales of a product in the low to mid-single digit percentages plus, once annual net sales exceed certain thresholds, a one-time cash payment upon reaching the thresholds. Therabiome must pay the Company royalties on annual net sales of any product Therabiome is permitted to develop using the intellectual property in the low double to mid-double-digit percentages, depending on the level of development or involvement the Company had in the product. Two regulatory milestones totaling $350,000 were determined to have occurred under this agreement and were paid during the nine months ended September 30, 2019. No amounts were accrued for this agreement as of and for the nine months ended September 30, 2018.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Lease Cost [Abstract]
Leases	Note 9 - Leases Operating Leases The Company leases office space for corporate and administrative functions in Carmel, Indiana under a lease agreement that expires in August 2023. The Company leases office and laboratory space in South San Francisco, California under a sub-sublease that expires in December 2023. Prior to moving into the South San Francisco office and laboratory space in February 2019, the Company leased office and laboratory space in San Francisco, California, under a sublease that expired on February 28, 2019. The Company also leases office and laboratory space in Groton, Connecticut under a lease that expires in March 2020. The Company’s China subsidiary leases office space in Shanghai that expires in May 2020 and rents lab space in Shanghai under a lease agreement that expires in December 2019. Additionally, the Company’s China subsidiary leases office space in Beijing under a lease agreement that expires in December 2019. Certain lease contracts contain renewal clauses that the Company assesses on a case by case basis. The Company also leases certain laboratory equipment accounted for as operating leases. These equipment leases began to expire in 2017, with the final lease expiring in 2021. When the Company cannot determine the implicit rate in its leasing arrangements, the Company uses its incremental borrowing rate as the discount rate when measuring operating lease liabilities. The incremental borrowing rate represents an estimate of the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease within a particular currency environment. At September 30, 2019, the Company had operating lease liabilities of $13.0 million and right-of-use assets of $12.8 million, which were included in the condensed consolidated balance sheet. The following summarizes quantitative information about the Company’s operating leases: ($ in thousands) Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Lease cost Operating lease cost $ 1,136 $ 3,344 Short-term lease cost 88 520 Variable lease cost 301 900 Total lease cost $ 1,525 $ 4,764 ($ in thousands) Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating cash flows from operating leases $ 1,089 $ 3,188 Right-of-use assets exchanged for new operating lease liabilities $ 928 $ 1,328 As of September 30, 2019, the weighted-average remaining lease term for operating leases was approximately 2.9 years and the weighted-average discount rate for operating leases was approximately 9.4%. As of September 30, 2019, the maturities of the Company’s operating lease liabilities were as follows (in thousands): Three months ended December 31, 2019 $ 4,361 Year Ended December 31, 2020 4,072 Year Ended December 31, 2021 3,532 Year Ended December 31, 2022 3,331 Year Ended December 31, 2023 806 Total 16,102 Less: present value discount (3,055 ) Operating lease liabilities $ 13,047 Operating lease costs were approximately $1.1 million and $3.3 million, for the three and nine months ended September 30, 2019, respectively and $0.8 million and $2.3 million for the three and nine months ended September 30, 2018, respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and pursuant to the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the U.S. Securities and Exchange Commission (SEC). In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements and include normal recurring adjustments necessary for the fair presentation of the Company’s financial position and its results of operations and comprehensive loss and its cash flows for the periods presented. These statements do not include all disclosures required by U.S. GAAP and should be read in conjunction with the Company’s audited consolidated financial statements and accompanying notes for the fiscal year ended December 31, 2018, which are contained in the Company’s Annual Report on Form 10-K as filed with the SEC on February 28, 2019. The results for the three and nine months ended September 30, 2019 are not necessarily indicative of results to be expected for the entire year ending December 31, 2019 or future operating periods.
Use of Estimates	Use of Estimates The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Significant estimates inherent in the preparation of the accompanying unaudited condensed consolidated financial statements include revenue recognition, clinical trial accruals, recoverability and useful lives (indefinite or finite) of intangible assets, assessment of impairment of goodwill, provisions for income taxes, amounts receivable and recognized as revenue under the Collaboration Agreement, measurement of operating lease liabilities, and the fair value of stock options, stock appreciation rights, and restricted stock units (RSUs) granted to employees, directors and consultants. The Company’s estimates could be affected by external conditions, including those unique to the Company and general economic conditions. It is reasonably possible that these external factors could have an effect on the Company’s estimates and could cause actual results to differ from those estimates and assumptions.
Significant Accounting Policies	Significant Accounting Policies There have been no material changes to the Company’s significant accounting policies from those described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, other than as set forth below.
Stock-Based Compensation	Stock-Based Compensation The Company expenses stock-based compensation to employees and Board members over the requisite service period based on the estimated grant-date fair value of the awards. Stock-based awards with graded-vesting schedules are recognized using the accelerated attribution method over the requisite service period for each separately vesting portion of the award. Prior to the adoption of Accounting Standards Update (ASU) 2018-07 (ASU 2018-07) on January 1, 2019, the Company remeasured the fair value of the non-employee awards at each reporting period prior to vesting and finally at the vesting date of the award. Changes in the estimated fair value of these non-employee awards were recognized as compensation expense in the period of change. Subsequent to the adoption of ASU 2018-07, the Company recognizes non-employee compensation costs over the requisite service period based on a measurement of fair value for each stock award. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model and the assumptions used in calculating the fair value of stock-based awards represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment. Forfeitures are recognized when incurred. The fair value of restricted stock units is determined based on the number of shares granted and the quoted market price of the Company’s common stock on the date of grant. The fair value of restricted stock units with performance conditions deemed probable of being achieved and vesting are amortized to expense over the requisite service period using the accelerated attribution method of expense recognition.
Leases	Leases All of the Company’s leases are operating leases for facilities and equipment. Prior to January 1, 2019, the Company recognized related rent expense on a straight-line basis over the term of the lease. Incentives granted under the Company’s facilities lease, including allowances for leasehold improvements and rent holidays, were recognized as reductions to rental expense on a straight-line basis over the term of the lease. Deferred rent consisted of the difference between cash payments and the rent expense recognized. Subsequent to the adoption of the new leasing standard on January 1, 2019, the Company recognizes a lease asset for its right to use the underlying asset and a lease liability for the corresponding lease obligation. The Company determines whether an arrangement is or contains a lease at contract inception. Operating leases are included in operating lease right-of-use assets, operating lease liabilities - short-term, and operating lease liabilities - long-term in the Company’s condensed consolidated balance sheet at September 30, 2019. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the net present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. The incremental borrowing rate represents the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably assured the Company will exercise the option to extend the contract. Periods covered by an option to extend are included in the lease term if the lessor controls the exercise of that option. The operating lease right-of-use assets also include any lease payments made and exclude lease incentives. Lease expense is recognized on a straight-line basis over the expected lease term. Variable lease expenses are recorded when incurred. The Company has elected not to separate lease and non-lease components for its leased assets and accounts for all lease and non-lease components of its agreements as a single lease component.
Net Loss per Share	Net Loss per Share Basic net loss per common share excludes dilution and is computed by dividing net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per common share reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the entity unless inclusion of such shares would be anti-dilutive. Since the Company has only incurred losses, basic and diluted net loss per share is the same. Securities that could potentially dilute loss per share in the future that were not included in the computation of diluted loss per share are as follows: Nine Months Ended September 30, 2019 2018 Warrants to purchase common stock 15,296 15,296 Options to purchase common stock 5,462,773 4,422,194 Common stock subject to purchase under ESPP 17,018 10,198 Unvested RSUs 668,515 343,465 Total 6,163,602 4,791,153 A reconciliation of the numerators and the denominators of the basic and diluted net loss per common share computations is as follows (in thousands, except per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net loss (in thousands) (24,995 ) (21,535 ) (70,550 ) (64,590 ) Denominator: Weighted average common shares outstanding for diluted net (loss) income per share 25,912,568 24,878,413 25,765,414 21,900,943 Net (loss) income per share: Basic (0.96 ) (0.87 ) (2.74 ) (2.95 ) Diluted (0.96 ) (0.87 ) (2.74 ) (2.95 )
Recent Accounting Pronouncements	Adoption of Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, Leases The Company adopted ASU 2016-02 on January 1, 2019 using the modified retrospective approach and elected the package of practical expedients permitted under transition guidance, which allowed the Company to carry forward its historical assessments of: (1) whether contracts are or contain leases, (2) lease classification and (3) initial direct costs. The Company did not elect the use-of-hindsight practical expedient, which would require the Company to reassess the lease term of its leases based on all facts and circumstances through the effective date, and the Company did not elect the practical expedient pertaining to land easements as this is not applicable to the Company’s current contract portfolio. The Company elected the post-transition practical expedient to not separate lease components from nonlease components for all existing lease classes. The Company also elected a policy of not recording leases on its condensed consolidated balance sheets when the leases have a term of 12 months or less and the Company is not reasonably certain to elect an option to purchase the leased asset. The adoption of this standard resulted in the recognition of right of use (ROU) assets and lease liabilities of $13.8 million and $14.0 million, respectively, and the derecognition of the deferred rent balance of $0.1 million as of January 1, 2019. The adoption of the standard had no impact on the Company’s condensed consolidated statements of operations and comprehensive loss or to its cash flows from or used in operating, financing, or investing activities on its condensed consolidated statements of cash flows. No cumulative-effect adjustment within accumulated deficit was required to be recorded as a result of adopting this standard. On January 1, 2019, the Company adopted ASU 2018-02, Income Statement - Reporting Comprehensive Income, (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, On January 1, 2019, the Company adopted ASU 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting Compensation – Stock Compensation In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification Recent Accounting Pronouncements In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement, In January 2017, the FASB issued ASU 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04), which simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. Under the amendments in ASU 2017-04, an entity should recognize an impairment charge for the amount by which the carrying amount of a reporting unit exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The updated guidance requires a prospective adoption. ASU 2017-04 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. The Company is currently evaluating the timing and impact of adopting this new accounting standard on its condensed consolidated financial statements and related disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326 Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments Financial Instruments - Credit Losses (Topic 326): Targeted Transition Relief

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	Securities that could potentially dilute loss per share in the future that were not included in the computation of diluted loss per share are as follows: Nine Months Ended September 30, 2019 2018 Warrants to purchase common stock 15,296 15,296 Options to purchase common stock 5,462,773 4,422,194 Common stock subject to purchase under ESPP 17,018 10,198 Unvested RSUs 668,515 343,465 Total 6,163,602 4,791,153
Schedule of Earnings Per Share, Basic and Diluted	A reconciliation of the numerators and the denominators of the basic and diluted net loss per common share computations is as follows (in thousands, except per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net loss (in thousands) (24,995 ) (21,535 ) (70,550 ) (64,590 ) Denominator: Weighted average common shares outstanding for diluted net (loss) income per share 25,912,568 24,878,413 25,765,414 21,900,943 Net (loss) income per share: Basic (0.96 ) (0.87 ) (2.74 ) (2.95 ) Diluted (0.96 ) (0.87 ) (2.74 ) (2.95 )

Investments in Marketable Sec_2

Investments in Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Schedule of Investments in Marketable Securities	Investments in marketable securities consisted of the following: September 30, 2019 ($ in thousands) Amortized Cost Gross Unrealized Gain (1) Gross Unrealized Loss (1) Fair Value Short-term available-for-sale securities U.S. and foreign corporate debt securities $ 34,111 $ 44 $ — $ 34,155 Asset-backed securities 22,117 16 — 22,133 U.S. treasury securities 27,008 16 (6 ) 27,018 U.S. and foreign commercial paper 48,764 — — 48,764 Total $ 132,000 $ 76 $ (6 ) $ 132,070 (1) Gross unrealized gain (loss) is pre-tax. December 31, 2018 ($ in thousands) Amortized Cost Gross Unrealized Gain (1) Gross Unrealized Loss (1) Fair Value Short-term available-for-sale securities U.S. and foreign corporate debt securities $ 73,251 $ — $ (92 ) $ 73,159 Asset-backed securities 28,450 — (31 ) 28,419 U.S. treasury securities 19,898 — (3 ) 19,895 U.S. and foreign commercial paper 55,136 — — 55,136 Total $ 176,735 $ — $ (126 ) $ 176,609 (1) Gross unrealized gain (loss) is pre-tax.
Schedule of Fair Value of Financial Assets	The following tables present the fair value of the Company’s financial assets measured at fair value on a recurring basis: September 30, 2019 ($ in thousands) Level 1 Level 2 Level 3 Fair Value Cash equivalents Money market fund $ 19,948 $ — $ — $ 19,948 Total cash equivalents 19,948 — — 19,948 Short-term investments U.S. and foreign corporate debt securities — 34,155 — 34,155 Asset-backed securities — 22,133 — 22,133 U.S. treasury securities — 27,018 — 27,018 U.S. and foreign commercial paper — 48,764 — 48,764 Total short-term investments — 132,070 — 132,070 Total assets measured at fair value $ 19,948 $ 132,070 $ — $ 152,018 December 31, 2018 ($ in thousands) Level 1 Level 2 Level 3 Fair Value Cash equivalents Money market fund $ 39,345 $ — $ — $ 39,345 Total cash equivalents 39,345 — — 39,345 Short-term investments U.S. and foreign corporate debt securities — 73,159 — 73,159 Asset-backed securities — 28,419 — 28,419 U.S. treasury securities — 19,895 — 19,895 U.S. and foreign commercial paper — 55,136 — 55,136 Total short-term investments — 176,609 — 176,609 Total assets measured at fair value $ 39,345 $ 176,609 $ — $ 215,954

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consist of the following: Useful life September 30, December 31, ($ in thousands) (Years) 2019 2018 Computer hardware and software 3 $ — $ 194 Lab equipment 3 to 5 230 407 Office equipment 7 699 70 Leasehold improvement 1 to 5 2,084 790 Total property, plant and equipment 3,013 1,461 Less: Accumulated depreciation and amortization (1,082 ) (1,057 ) Construction in progress N/A — 153 Property, plant and equipment, net $ 1,931 $ 557

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following: September 30, December 31, ($ in thousands) 2019 2018 Accrued expenses: Accrued compensation $ 4,042 $ 5,011 Accrued clinical trial expenses 4,321 3,561 Accrued professional fees and other 1,067 1,107 Total accrued expenses $ 9,430 $ 9,679

Stock Plans and Stock-Based C_2

Stock Plans and Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock Options Activity	A summary of the Company’s option activity and related information for the nine months ended September 30, 2019 is as follows: Number of Shares Weighted Average Exercise Price Per Share Total Intrinsic Value (in thousands) Outstanding as of December 31, 2018 4,637,145 $ 17.21 $ 48,179 Granted 1,418,350 15.74 — Exercised (243,481 ) 7.05 1,642 Forfeited (346,741 ) 44.85 117 Expired (2,500 ) 49.14 — Outstanding as of September 30, 2019 5,462,773 $ 15.52 $ 9,000 Options vested and exercisable 3,278,755 $ 12.01 $ 8,656
Schedule of RSU's	A summary of the Company’s RSUs and related information for the nine months ended September 30, 2019 is as follows: Number of RSU's Weighted Average Grant Price Outstanding as of December 31, 2018 568,005 $ 37.18 Granted 435,928 15.24 Vested and settled (97,254 ) 45.05 Forfeited (126,497 ) 24.41 Outstanding as of September 30, 2019 780,182 (1) $ 26.01 (1) Includes 111,667 RSUs that have vested but are subject to deferred settlement.
Assumptions for Weighted Average Fair Value of Options Granted	The fair value of the stock options granted or modified during the periods indicated was estimated using the Black-Scholes option pricing model, based on the following assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Exercise price $10.91 - $49.14 $38.88 - $41.25 $10.91 - $49.14 $38.88 - $57.53 Expected volatility 66.4% - 80.6% 76.0% - 84.5% 66.4% - 83.2% 76.0% - 86.1% Risk-free rate 1.36% - 1.89% 2.75% - 2.94% 1.36% - 2.65% 2.56% - 2.94% Expected term (years) 5.5 - 9.6 5.5 - 7.0 5.5 - 9.6 5.5 - 7.0 Dividend yield 0% 0% 0% 0%
Schedule of Stock-Based Compensation Expense	The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss: Three Months Ended September 30, Nine Months Ended September 30, ($ in thousands) 2019 2018 2019 2018 Research and development $ 2,464 $ 2,474 $ 8,309 $ 8,687 General and administrative 2,940 3,532 5,740 (1) 12,991 Total stock-based compensation expense $ 5,404 $ 6,006 $ 14,049 $ 21,678 (1) Includes the reversal of previously recognized expense of $3.6 million related to forfeited awards resulting from the departure of one of our former officers during the period.

Collaboration Agreement (Tables

Collaboration Agreement (Tables)	9 Months Ended
	Sep. 30, 2019
Collaboration Agreement [Abstract]
Schedule of Changes in Contract Liabilities	The following table presents changes in the Company’s contract liabilities ($ in thousands): Balance at Beginning of Period Additions Deductions Balance at End of Period Nine Months Ended September 30, 2019 Contract liabilities: Deferred revenue $ 40,660 $ — $ (2,241 ) $ 38,419 Balance at Beginning of Period Additions Deductions Balance at End of Period Nine Months Ended September 30, 2018 Contract liabilities: Deferred revenue $ 45,785 $ — $ (3,861 ) $ 41,924
Schedule of Collaboration Revenue Recognized with the Period	Three Months Ended September 30, Nine Months Ended September 30, ($ in thousands) 2019 2018 2019 2018 Collaboration revenue recognized in the period from Amounts included in deferred revenue at the beginning of the period 1,245 1,666 2,241 3,861 Performance obligations satisfied in previous period — — — —

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Lease Cost [Abstract]
Schedule of Quantitative Information of Operating Leases	The following summarizes quantitative information about the Company’s operating leases: ($ in thousands) Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Lease cost Operating lease cost $ 1,136 $ 3,344 Short-term lease cost 88 520 Variable lease cost 301 900 Total lease cost $ 1,525 $ 4,764 ($ in thousands) Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating cash flows from operating leases $ 1,089 $ 3,188 Right-of-use assets exchanged for new operating lease liabilities $ 928 $ 1,328
Schedule of Maturities Operating Lease Liabilities	As of September 30, 2019, the maturities of the Company’s operating lease liabilities were as follows (in thousands): Three months ended December 31, 2019 $ 4,361 Year Ended December 31, 2020 4,072 Year Ended December 31, 2021 3,532 Year Ended December 31, 2022 3,331 Year Ended December 31, 2023 806 Total 16,102 Less: present value discount (3,055 ) Operating lease liabilities $ 13,047

Nature of Business - Additional

Nature of Business - Additional Information (Details)	9 Months Ended
	Sep. 30, 2019segmentproduct
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Operating segments (in segments) | segment	1
FDA approved products (in products) | product	0

Summary of Significant Accoun_4

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	6,163,602	4,791,153
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	15,296	15,296
Options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	5,462,773	4,422,194
Common stock subject to purchase under ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	17,018	10,198
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	668,515	343,465

Summary of Significant Accoun_5

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net loss (in thousands)	$ (24,995)	$ (21,535)	$ (70,550)	$ (64,590)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share	25,912,568	24,878,413	25,765,414	21,900,943
Net (loss) income per share:
Basic	$ (0.96)	$ (0.87)	$ (2.74)	$ (2.95)
Diluted	$ (0.96)	$ (0.87)	$ (2.74)	$ (2.95)

Summary of Significant Accoun_6

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2019	Jan. 01, 2019
Accounting Policies [Abstract]
Lessee, operating lease, term of contract			12 months
Operating lease, right-of-use asset	$ 0	$ 12,783	$ 13,800
Operating lease, liability		$ 13,047	14,000
Deferred rent credit			$ 100
Statutory federal tax rate (as percent)	21.00%

Investments in Marketable Sec_3

Investments in Marketable Securities - Schedule of Investments in Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investments in marketable securities:
Amortized Cost	$ 132,000	$ 176,735
Gross Unrealized Gain	76	0
Gross Unrealized Loss	(6)	(126)
Fair Value	132,070	176,609
U.S and foreign corporate debt securities
Investments in marketable securities:
Amortized Cost	34,111	73,251
Gross Unrealized Gain	44	0
Gross Unrealized Loss	0	(92)
Fair Value	34,155	73,159
Asset-backed securities
Investments in marketable securities:
Amortized Cost	22,117	28,450
Gross Unrealized Gain	16	0
Gross Unrealized Loss	0	(31)
Fair Value	22,133	28,419
U.S. treasury securities
Investments in marketable securities:
Amortized Cost	27,008	19,898
Gross Unrealized Gain	16	0
Gross Unrealized Loss	(6)	(3)
Fair Value	27,018	19,895
U.S. and foreign commercial paper
Investments in marketable securities:
Amortized Cost	48,764	55,136
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	$ 48,764	$ 55,136

Investments in Marketable Sec_4

Investments in Marketable Securities - Additional Information (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Investments in marketable securities:
Long-term marketable securities	$ 0
Fair value assets transfers between level 1, level 2 or level 3	$ 0	$ 0
Short Term Investments
Investments in marketable securities:
Available for sale securities maturity term	less than one year

Investments in Marketable Sec_5

Investments in Marketable Securities - Schedule of Fair Value of Financial Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Short-term investments
Short-term investments	$ 132,070	$ 176,609
U.S and foreign corporate debt securities
Short-term investments
Short-term investments	34,155	73,159
Asset-backed securities
Short-term investments
Short-term investments	22,133	28,419
U.S. treasury securities
Short-term investments
Short-term investments	27,018	19,895
U.S. and foreign commercial paper
Short-term investments
Short-term investments	48,764	55,136
Recurring
Cash equivalents
Money market fund	19,948	39,345
Short-term investments
Short-term investments	132,070	176,609
Total assets measured at fair value	152,018	215,954
Recurring | U.S and foreign corporate debt securities
Short-term investments
Short-term investments	34,155	73,159
Recurring | Asset-backed securities
Short-term investments
Short-term investments	22,133	28,419
Recurring | U.S. treasury securities
Short-term investments
Short-term investments	27,018	19,895
Recurring | U.S. and foreign commercial paper
Short-term investments
Short-term investments	48,764	55,136
Recurring | Money market fund
Cash equivalents
Money market fund	19,948	39,345
Recurring | Level 1
Cash equivalents
Money market fund	19,948	39,345
Short-term investments
Short-term investments	0	0
Total assets measured at fair value	19,948	39,345
Recurring | Level 1 | U.S and foreign corporate debt securities
Short-term investments
Short-term investments	0	0
Recurring | Level 1 | Asset-backed securities
Short-term investments
Short-term investments	0	0
Recurring | Level 1 | U.S. treasury securities
Short-term investments
Short-term investments	0	0
Recurring | Level 1 | U.S. and foreign commercial paper
Short-term investments
Short-term investments	0	0
Recurring | Level 1 | Money market fund
Cash equivalents
Money market fund	19,948	39,345
Recurring | Level 2
Cash equivalents
Money market fund	0	0
Short-term investments
Short-term investments	132,070	176,609
Total assets measured at fair value	132,070	176,609
Recurring | Level 2 | U.S and foreign corporate debt securities
Short-term investments
Short-term investments	34,155	73,159
Recurring | Level 2 | Asset-backed securities
Short-term investments
Short-term investments	22,133	28,419
Recurring | Level 2 | U.S. treasury securities
Short-term investments
Short-term investments	27,018	19,895
Recurring | Level 2 | U.S. and foreign commercial paper
Short-term investments
Short-term investments	48,764	55,136
Recurring | Level 2 | Money market fund
Cash equivalents
Money market fund	0	0
Recurring | Level 3
Cash equivalents
Money market fund	0	0
Short-term investments
Short-term investments	0	0
Total assets measured at fair value	0	0
Recurring | Level 3 | U.S and foreign corporate debt securities
Short-term investments
Short-term investments	0	0
Recurring | Level 3 | Asset-backed securities
Short-term investments
Short-term investments	0	0
Recurring | Level 3 | U.S. treasury securities
Short-term investments
Short-term investments	0	0
Recurring | Level 3 | U.S. and foreign commercial paper
Short-term investments
Short-term investments	0	0
Recurring | Level 3 | Money market fund
Cash equivalents
Money market fund	$ 0	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment
Total property, plant and equipment	$ 3,013	$ 1,461
Less: Accumulated depreciation and amortization	(1,082)	(1,057)
Property, plant and equipment, net	$ 1,931	557
Computer hardware and software
Property, Plant and Equipment
Total property, plant and equipment		194
Useful Life (in years)	3 years
Lab equipment
Property, Plant and Equipment
Total property, plant and equipment	$ 230	407
Lab equipment | Minimum
Property, Plant and Equipment
Useful Life (in years)	3 years
Lab equipment | Maximum
Property, Plant and Equipment
Useful Life (in years)	5 years
Office equipment
Property, Plant and Equipment
Total property, plant and equipment	$ 699	70
Useful Life (in years)	7 years
Leasehold improvement
Property, Plant and Equipment
Total property, plant and equipment	$ 2,084	790
Leasehold improvement | Minimum
Property, Plant and Equipment
Useful Life (in years)	1 year
Leasehold improvement | Maximum
Property, Plant and Equipment
Useful Life (in years)	5 years
Construction in progress
Property, Plant and Equipment
Total property, plant and equipment		$ 153

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation	$ 0.1	$ 0.2	$ 0.4	$ 0.5

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued expenses:
Accrued compensation	$ 4,042	$ 5,011
Accrued clinical trial expenses	4,321	3,561
Accrued professional fees and other	1,067	1,107
Total accrued expenses	$ 9,430	$ 9,679

Stock Plans and Stock-Based C_3

Stock Plans and Stock-Based Compensation - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended			9 Months Ended
	Sep. 30, 2019	May 31, 2019	May 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Shares reserved for issuance (in shares)		3,000,000	1,900,000
Maximum shares available by employee (in shares)			400,000
Purchase price after discount (in percent)			85.00%
Stock-based compensation expense					$ 5,404		$ 6,006	$ 14,049	$ 21,678
RSUs
Share-based Compensation Arrangement by Share-based Payment Award
Granted								435,928
Forfeited								126,497
Unrecognized stock-based compensation expense	$ 10,200				$ 10,200			$ 10,200
RSUs | Executives
Share-based Compensation Arrangement by Share-based Payment Award
Granted	100,000			45,000
RSUs | Former Officer
Share-based Compensation Arrangement by Share-based Payment Award
Forfeited						100,000
Grant date fair value						$ 2,400
Stock-based compensation expense						$ (400)
Options
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock under employee stock purchase plan ( in shares )		36,804

Stock Plans and Stock-Based C_4

Stock Plans and Stock-Based Compensation - Schedule of Stock Options Activity (Details) - Options - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2019
Number of Shares
Option, Outstanding at beginning of period	4,637,145
Option, Granted	1,418,350
Option, Exercised	(243,481)
Option, Forfeited	(346,741)
Option, Expired	(2,500)
Option, Outstanding at end of period	5,462,773
Options vested and exercisable	3,278,755
Weighted Average Exercise Price
Option, Outstanding at beginning of period	$ 17.21
Option, Granted	15.74
Option, Exercised	7.05
Option, Forfeited	44.85
Option, Expired	49.14
Option, Outstanding at end of period	15.52
Options vested and exercisable	$ 12.01
Total Intrinsic Value
Option, Outstanding at beginning of period	$ 48,179
Option, Granted	0
Option, Exercised	1,642
Option, Forfeited	117
Option, Expired	0
Option, Outstanding at end of period	9,000
Options vested and exercisable	$ 8,656

Stock Plans and Stock-Based C_5

Stock Plans and Stock-Based Compensation - Schedule of RSU's (Details) - RSUs	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Number of Shares
Beginning of period | shares	568,005
Granted | shares	435,928
Vested and settled | shares	(97,254)
Forfeited | shares	(126,497)
Ending of period | shares	780,182
Weighted average grant price
Beginning of period | $ / shares	$ 37.18
Granted | $ / shares	15.24
Vested and settled | $ / shares	45.05
Forfeited | $ / shares	24.41
Ending of period | $ / shares	$ 26.01

Stock Plans and Stock-Based C_6

Stock Plans and Stock-Based Compensation - Schedule of RSU's (Parenthetical) (Details)	9 Months Ended
	Sep. 30, 2019shares
RSUs
Share-based Compensation Arrangement by Share-based Payment Award
Vested and subject to deferred settlement	111,667

Stock Plans and Stock-Based C_7

Stock Plans and Stock-Based Compensation - Assumptions for Weighted Average Fair Value of Options Granted (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price	$ 10.91	$ 38.88	$ 10.91	$ 38.88
Expected volatility	66.40%	76.00%	66.40%	76.00%
Risk-free rate	1.36%	2.75%	1.36%	2.56%
Expected term (years)	5 years 6 months	5 years 6 months	5 years 6 months	5 years 6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price	$ 49.14		$ 49.14
Exercise price		$ 41.25		$ 57.53
Expected volatility	80.60%	84.50%	83.20%	86.10%
Risk-free rate	1.89%	2.94%	2.65%	2.94%
Expected term (years)	9 years 7 months 6 days	7 years	9 years 7 months 6 days	7 years

Stock Plans and Stock-Based C_8

Stock Plans and Stock-Based Compensation -Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Compensation expense:
Stock-based compensation expense	$ 5,404	$ 6,006	$ 14,049	$ 21,678
Research and Development
Compensation expense:
Stock-based compensation expense	2,464	2,474	8,309	8,687
General and administrative
Compensation expense:
Stock-based compensation expense	$ 2,940	$ 3,532	$ 5,740	$ 12,991

Stock Plans and Stock-Based C_9

Stock Plans and Stock-Based Compensation -Schedule of Stock-Based Compensation Expense (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	$ 5,404	$ 6,006	$ 14,049	$ 21,678
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	$ 2,940	$ 3,532	5,740	$ 12,991
Former Officer | General and administrative
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense			$ (3,600)

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Details) $ in Thousands	Feb. 10, 2017USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)Milestone	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Collaboration Agreements:
Collaboration revenue		$ 4,231	$ 4,286	$ 11,197	$ 11,069
Contract with customer, liability, current		6,151		6,151		$ 5,100
Contract with customer, liability, noncurrent		32,268		32,268		35,560
Accounts receivable from collaboration		2,944		2,944		2,430
Allergan
Collaboration Agreements:
Agreed to share maximum amount development cost	$ 75,000
Premium percentage on agreed contribution development cost amount	25.00%
Collaborative Arrangement
Collaboration Agreements:
Collaboration revenue	$ 50,000			12,500
Cost of reimbursable expenses				11,200	$ 11,100
Contract with customer, liability, current		6,200		6,200		5,100
Contract with customer, liability, noncurrent		$ 32,300		32,300		$ 35,600
Collaborative Arrangement | Milestone Scenario One
Collaboration Agreements:
Potential milestone payments				$ 631,000
Number of milestones | Milestone				7
Collaborative Arrangement | Milestone Scenario Two
Collaboration Agreements:
Potential milestone payments				$ 2,140,000
Number of milestones | Milestone				12

Collaboration Agreement - Sched

Collaboration Agreement - Schedule of Changes in Contract Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Collaboration Agreement [Abstract]
Balance at Beginning of Period	$ 40,660	$ 45,785
Additions	0	0
Deductions	(2,241)	(3,861)
Balance at End of Period	$ 38,419	$ 41,924

Collaboration Agreement - Sch_2

Collaboration Agreement - Schedule of Collaboration Revenue Recognized with the Period (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Collaboration revenue recognized in the period from
Amounts included in deferred revenue at the beginning of the period	$ 1,245	$ 1,666	$ 2,241	$ 3,861
Performance obligations satisfied in previous period	$ 0	$ 0	$ 0	$ 0

Milestones and Research Agree_2

Milestones and Research Agreements - Additional Information (Details)	9 Months Ended
	Sep. 30, 2019USD ($)Milestone	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)
Milestone and Research Agreements:
Potential milestone payment	$ 800,000
Accrued expenses	9,430,000	$ 9,679,000
Microbiome Targeted Colonic Delivery Program
Milestone and Research Agreements:
Potential milestone payment	$ 350,000
Number of milestones | Milestone	2
Accrued expenses			$ 0

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease, liability	$ 13,047		$ 13,047		$ 14,000
Operating lease, right-of-use asset	$ 12,783		$ 12,783		$ 13,800	$ 0
Weighted-average remaining lease term - operating leases	2 years 10 months 24 days		2 years 10 months 24 days
Weighted-average discount rate - operating leases	9.40%		9.40%
Operating lease cost	$ 1,136	$ 800	$ 3,344	$ 2,300

Leases - Schedule of Quantitati

Leases - Schedule of Quantitative Information of Operating Leases (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Lease cost
Operating lease cost	$ 1,136	$ 800	$ 3,344	$ 2,300
Short-term lease cost	88		520
Variable lease cost	301		900
Total lease cost	1,525		4,764
Operating cash flows from operating leases	1,089		3,188
Right-of-use assets exchanged for new operating lease liabilities	$ 928		$ 1,328

Leases - Schedule of Maturities

Leases - Schedule of Maturities Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019
Lease Cost [Abstract]
Three months ended December 31, 2019	$ 4,361
Year Ended December 31, 2020	4,072
Year Ended December 31, 2021	3,532
Year Ended December 31, 2022	3,331
Year Ended December 31, 2023	806
Total	16,102
Less: present value discount	(3,055)
Operating lease liabilities	$ 13,047	$ 14,000