0001564590-20-023566 | 10-Q | XBRL Viewer

Document And Entity Information - shares	3 Months Ended
Document And Entity Information - shares	Mar. 31, 2020	May 04, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2020
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	331 Oyster Point Blvd.
Entity Address, Address Line Two	Fourth Floor
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	833
Local Phone Number	509-4583
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
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	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		32,722,365
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	true

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 42,326	$ 46,732
Marketable securities	206,803	227,311
Accounts receivable from collaboration	3,055	3,374
Prepaid expenses and other current assets	4,568	5,363
Total current assets	256,752	282,780
Property and equipment, net	1,780	1,830
Operating lease right-of-use (ROU) assets	11,479	11,975
Other assets	1,661	1,684
Indefinite-lived intangible asset	29,000	29,000
Goodwill	12,638	12,638
Total assets	313,310	339,907
Current liabilities
Accounts payable	2,104	1,731
Accrued clinical expenses	4,633	4,826
Other accrued expenses	4,430	8,286
Deferred revenue - short-term	6,715	6,411
Operating lease liabilities - short-term	3,264	3,186
Total current liabilities	21,146	24,440
Deferred tax liabilities	2,531	2,531
Deferred revenue - long-term	29,326	30,637
Operating lease liabilities - long-term	8,539	9,082
Total liabilities	61,542	66,690
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 March 31, 2020 and December 31, 2019; 32,624,725 and 32,558,307 shares issued and outstanding as of March 31, 2020 and December 31, 2019, respectively	32	32
Additional paid-in capital	717,898	712,807
Accumulated other comprehensive loss	(86)	(201)
Accumulated deficit	(466,076)	(439,421)
Total stockholders' equity	251,768	273,217
Total liabilities and stockholders' equity	$ 313,310	$ 339,907

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	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	32,624,725	32,558,307
Common stock, shares outstanding	32,624,725	32,558,307

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Collaboration revenue	$ 4,081	$ 3,885
Operating expenses:
Research and development	23,046	22,704
General and administrative	8,729	9,517
Total operating expenses	31,775	32,221
Loss from operations	(27,694)	(28,336)
Other income
Interest and other income, net	1,039	1,277
Total other income	1,039	1,277
Loss before income taxes	(26,655)	(27,059)
Income tax benefit		7
Net loss	(26,655)	(27,052)
Other comprehensive (loss) income
Unrealized gain on marketable securities, net of tax	115	108
Comprehensive loss	$ (26,540)	$ (26,944)
Net loss per share, basic and diluted	$ (0.76)	$ (1.05)
Weighted average common shares outstanding, basic and diluted	35,079,756	25,668,798

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (26,655)	$ (27,052)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	115	135
Stock-based compensation	4,924	6,577
Net accretion and amortization of investments in marketable securities	(135)	(592)
Non-cash rent expense	1,151	1,091
Deferred income tax benefit	0	(7)
Loss on disposal of fixed assets	0	102
Other	0	(1)
Changes in operating assets and liabilities:
Accounts receivable from collaboration	319	(557)
Prepaid expenses and other current assets	795	(2,558)
Other assets	23	1,687
Accounts payable	373	(1,266)
Accrued clinical expenses	(193)	3,077
Other accrued expenses	(3,808)	(2,679)
Deferred revenue	(1,007)	(859)
Operating lease liabilities	(1,120)	(1,037)
Net cash used in operating activities	(25,218)	(23,939)
Cash flows from investing activities
Purchases of property and equipment	(65)	(1,488)
Purchases of marketable securities	(44,242)	(49,030)
Proceeds from maturities of marketable securities	55,000	61,453
Proceeds from sale of marketable securities	10,000	500
Net cash provided by investing activities	20,693	11,435
Cash flows from financing activities
Proceeds from the exercise of stock options	119	140
Net cash provided by financing activities	119	140
Net decrease in cash and cash equivalents	(4,406)	(12,364)
Cash and cash equivalents at the beginning of the period	46,732	41,471
Cash and cash equivalents at the end of the period	42,326	29,107
Supplemental non-cash investing and financing activities
Operating lease liabilities arising from obtaining ROU assets	$ 362	$ 13,933

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, 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	140		140
Issuance of common stock upon exercise of stock options (in shares)		21,000
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)		33,332
Settlement of RSUs for cash	(4)		(4)
Unrealized gain on marketable securities, net of tax	108			108
Stock-based compensation	6,556		6,556
Net loss	(27,052)				(27,052)
Balance at Mar. 31, 2019	190,401	$ 26	559,453	(239)	(368,839)
Balance (in shares) at Mar. 31, 2019		25,549,757
Balance at Dec. 31, 2019	273,217	$ 32	712,807	(201)	(439,421)
Balance (in shares) at Dec. 31, 2019		32,558,307
Issuance of common stock upon exercise of stock options	119		119
Issuance of common stock upon exercise of stock options (in shares)		16,834
Issuance of shares of common stock for settlement of restricted stock units (RSUs) (in shares)		49,584
Unrealized gain on marketable securities, net of tax	115			115
Stock-based compensation	4,972		4,972
Net loss	(26,655)				(26,655)
Balance at Mar. 31, 2020	$ 251,768	$ 32	$ 717,898	$ (86)	$ (466,076)
Balance (in shares) at Mar. 31, 2020		32,624,725

Nature of Business

3 Months Ended

Mar. 31, 2020

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 advancing two innovative programs: a novel class of oral therapeutic candidates targeting chronic hepatitis B virus (HBV) infection and a novel class of oral live microbial biotherapeutic candidates, which are designed to treat disorders associated with the microbiome. The Company operates in one segment and is headquartered in South San Francisco, California, with operations in South San Francisco, California and Groton, Connecticut. Prior to January 1, 2020, the Company was headquartered in Carmel, Indiana, and the Company expects to continue maintaining this office for a period of time.

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 chronic HBV infection. Assembly has discovered several novel core inhibitors, which are small molecules that directly target and allosterically modify the HBV core protein.

The Company’s Microbiome program is centered on a fully integrated platform that includes a biological function-based strain isolation, identification, characterization and selection process, methods for strain purification and growth under conditions compliant with current Good Manufacturing Practice (cGMP) requirements. That platform is complemented by a licensed patented delivery system that the Company calls 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, 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). Assembly is also exploring the microbiome in connection with immune-mediated and metabolic disorders and oncology, which indications the Company will either pursue 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, proceeds from the exercise of warrants and stock options, 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 12 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 (see Note 6 for recent sales of common stock). The Company cannot assure such funding will be available on reasonable terms, if at all. Market volatility resulting from the COVID-19 pandemic or other factors could also adversely impact the Company’s ability to access capital when and as needed.

If the Company is unable to generate sufficient revenue from the Collaboration Agreement, secure additional sources of funding or receive 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 Accounting Policies and Recent Accounting Pronouncements

3 Months Ended

Mar. 31, 2020

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, 2019, which are contained in the Company’s Annual Report on Form 10-K as filed with the SEC on March 4, 2020. The results for the three months ended March 31, 2020 are not necessarily indicative of results to be expected for the entire year ending December 31, 2020 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.

Other Risks and Uncertainties

In March 2020, the World Health Organization declared the global novel coronavirus disease (COVID-19) outbreak a pandemic. To date, the Company’s operations have not been significantly impacted by the COVID-19 outbreak. However, the Company cannot at this time predict the specific extent, duration, or full impact that the COVID-19 outbreak will have on its condensed consolidated financial condition and operations. The impact of the COVID-19 coronavirus outbreak on the financial performance of the Company will depend on future developments, including the duration and spread of the outbreak and related governmental advisories and restrictions. These developments and the impact of COVID-19 on the financial markets and the overall economy are highly uncertain. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be adversely affected.

Income Taxes

On March 18, 2020, the Families First Coronavirus Response Act (“FFCR Act”), and on March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) were each enacted in response to the COVID-19 pandemic. The FFCR Act and the CARES Act contain numerous income tax provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. The FFCR Act and CARES Act did not

have a material impact on the Company’s condensed consolidated financial statements as of March 31, 2020; however, the Company continues to examine the impacts the FFCR Act and CARES Act may have on its business, results of operations, financial condition and liquidity.

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.

In December 2019, the Company sold 6,287,878 shares of common stock as well as pre-funded warrants to purchase up to 2,424,242 shares of common stock (see Note 6). The pre-funded warrants are exercisable for shares of common stock at a price of $0.001 per share. The shares of common stock into which the pre-funded warrants may be exercised are considered outstanding for the purposes of computing earnings per share because the shares may be issued for little or no consideration, they are fully vested, and are exercisable after the original issuance date.

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 March 31,
	2020			2019
Numerator:
Net loss		(26,655	)		(27,052	)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share		35,079,756			25,668,798
Net (loss) income per share:
Basic		(0.76	)		(1.05	)
Diluted		(0.76	)		(1.05	)

Securities that could potentially dilute loss per share in the future that were not included in the computation of diluted loss per share because including them would have been antidilutive are as follows:

	Three Months Ended March 31,
	2020		2019
Warrants to purchase common stock		15,296		15,296
Options to purchase common stock		6,370,396		5,111,590
Common stock subject to purchase under our ESPP		32,940		22,432
Unvested RSUs		999,926		607,656
Total		7,418,558		5,756,974

Adoption of Recent Accounting Pronouncements

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. In November 2019, the FASB issued ASU 2019-10, Financial Instruments – Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates (ASU 2019-10), which deferred the effective

date of this standard for all entities except SEC filers that are not smaller reporting companies to fiscal years beginning after December 15, 2022, 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 early adopted ASU 2017-04 effective January 1, 2020. The adoption of this standard had no impact on the Company’s condensed consolidated financial statements.

On January 1, 2020, the Company adopted ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement, which makes a number of changes meant to add, modify or remove certain disclosure requirements associated with the movement amongst or hierarchy associated with Level 1, Level 2 and Level 3 fair value measurements. The adoption of this standard had no impact on the Company’s condensed consolidated financial statements and related disclosures.

On January 1, 2020, the Company adopted ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606, which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under Topic 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in Topic 606 should be applied, including recognition, measurement, presentation, and disclosure requirements. The standard adds unit-of-account guidance in Topic 808 to align with the guidance in Topic 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of Topic 606 and requires that in a transaction with a collaborative arrangement participant that is not directly related to sales to third parties, presenting the transaction together with revenue recognized under Topic 606 is precluded if the collaborative arrangement participant is not a customer. Amendments in the standard should be applied retrospectively to the date of initial application of Topic 606, but entities may elect to apply the amendments in Topic 808 retrospectively either to all contracts or only to contracts that are not completed at the date of initial application of Topic 606, and should disclose the election. An entity may also elect to apply the practical expedient for contract modifications that is permitted for entities using the modified retrospective transition method in Topic 606. The adoption of this standard had no impact on the Company’s condensed consolidated financial statements and related disclosures.

In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (ASU 2019-12). The ASU eliminates certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The new guidance also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. The standard is effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. Early adoption is permitted in an interim or annual period. Entities that elect to early adopt the amendments in an interim period should reflect any adjustments as of the beginning of the annual period that includes that interim period. Additionally, entities that elect early adoption must adopt all the amendments in the same period. Entities will apply the guidance prospectively, except for certain amendments. The Company early adopted ASU 2019-12 effective January 1, 2020. The adoption of this standard did not have a material impact on the Company’s condensed consolidated financial statements and related disclosures.

Recent Accounting Pronouncements

In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments (ASU 2016-13), which requires that expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities be recorded through an allowance for credit losses. ASU 2016-13 limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and also requires the reversal of previously recognized credit losses if fair value increases. In April, May and November 2019, the FASB issued additional amendments to the new guidance related to transition and clarification. In November 2019, the FASB issued ASU 2019-10, which deferred the effective date of this standard for all entities except SEC filers that are not smaller reporting companies to fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating this new accounting standard but currently does not expect the adoption of this standard to have a material impact on its condensed consolidated financial statements and related disclosures.

Investments in Marketable Securities

3 Months Ended

Mar. 31, 2020

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 (in thousands):

	March 31, 2020
	Amortized Cost		Gross Unrealized Gain ⁽¹⁾		Gross Unrealized Loss ⁽¹⁾			Fair Value
Cash equivalents
Money market funds	$	39,010	$	—	$	—		$	39,010
Total cash equivalents		39,010		—		—			39,010
Short-term investments
U.S. and foreign corporate debt securities		63,354		10		(121	)		63,243
Asset-backed securities		34,893		9		(44	)		34,858
U.S. treasury securities		44,637		368		—			45,005
U.S. and foreign commercial paper		63,697		—		—			63,697
Total short-term investments		206,581		387		(165	)		206,803
Total cash equivalents and investments	$	245,591	$	387	$	(165	)	$	245,813

(1)	Gross unrealized gain (loss) is pre-tax.

	December 31, 2019
	Amortized Cost		Gross Unrealized Gain ⁽¹⁾		Gross Unrealized Loss ⁽¹⁾			Fair Value
Cash equivalents
Money market funds	$	33,095	$	—	$	—		$	33,095
U.S. and foreign corporate debt securities		5,000		—		(1	)		4,999
U.S. and foreign commercial paper		4,484		—		—			4,484
Total cash equivalents		42,579		—		(1	)		42,578
Short-term investments
U.S. and foreign corporate debt securities		72,452		38		(4	)		72,486
Asset-backed securities		34,008		17		—			34,025
U.S. treasury securities		44,692		24		(2	)		44,714
U.S. and foreign commercial paper		76,086		—		—			76,086
Total short-term investments		227,238		79		(6	)		227,311
Total cash equivalents and investments	$	269,817	$	79	$	(7	)	$	269,889

(1)	Gross unrealized gain (loss) is pre-tax.

The contractual term to maturity of short-term marketable securities held by the Company as of March 31, 2020 is less than one year. There were no long-term marketable securities held by the Company as of March 31, 2020.

Realized gains and losses for the three months ended March 31, 2020 and 2019 were not significant. None of the Company’s investments have been in a continuous unrealized loss position for more than 12 months as of March 31, 2020.

The following tables present the fair value of the Company’s financial assets measured at fair value on a recurring basis (in thousands):

	March 31, 2020
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	39,010	$	—	$	—	$	39,010
Total cash equivalents		39,010		—		—		39,010
Short-term investments
U.S. and foreign corporate debt securities		—		63,243		—		63,243
Asset-backed securities		—		34,858		—		34,858
U.S. treasury securities		—		45,005		—		45,005
U.S. and foreign commercial paper		—		63,697		—		63,697
Total short-term investments		—		206,803		—		206,803
Total assets measured at fair value	$	39,010	$	206,803	$	—	$	245,813

	December 31, 2019
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund		33,095		—		—		33,095
U.S and foreign corporate debt securities		—		4,999		—		4,999
U.S and foreign commercial paper		—		4,484		—		4,484
Total cash equivalents		33,095		9,483		—		42,578
Short-term investments
U.S. and foreign corporate debt securities		—		72,486		—		72,486
Asset-backed securities		—		34,025		—		34,025
U.S. treasury securities		—		44,714		—		44,714
U.S. and foreign commercial paper		—		76,086		—		76,086
Total short-term investments		—		227,311		—		227,311
Total assets measured at fair value	$	33,095	$	236,794	$	—	$	269,889

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

3 Months Ended

Mar. 31, 2020

Property Plant And Equipment [Abstract]

Property and Equipment, Net

Note 4 - Property and Equipment, Net

Property and equipment consist of the following (in thousands):

	Useful life	March 31,			December 31,
	(Years)	2020			2019
Lab equipment	3 to 5	$	286		$	247
Office equipment	7		699			699
Leasehold improvement	1 to 5		2,084			2,084
Total property and equipment			3,069			3,030
Less: Accumulated depreciation and amortization			(1,315	)		(1,200	)
Construction in progress	N/A		26			-
Property and equipment, net		$	1,780		$	1,830

Depreciation expense was $0.1 million for both the three months ended March 31, 2020 and 2019 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. Primarily all of property and equipment of the Company is located in the U.S.

Accrued Expenses

3 Months Ended

Mar. 31, 2020

Payables And Accruals [Abstract]

Accrued Expenses

Note 5 – Accrued Expenses

Accrued expenses consist of the following (in thousands):

	March 31,		December 31,
	2020		2019
Accrued expenses:
Accrued compensation	$	2,144	$	5,312
Accrued restructuring charges		1,627		2,094
Accrued professional fees and other		659		880
Total accrued expenses	$	4,430	$	8,286

Accrued restructuring charges relate to the Company’s decision to relocate its headquarters and key personnel to South San Francisco, California as approved by the Board of Directors in November 2019 and effective January 1, 2020. The Company accrued restructuring charges of $2.1 million in 2019 related to one-time severance payments and other employee-related costs associated with the relocation plan. This represents the total amount expected to be incurred in connection with the relocation and is expected to be fully paid in 2020.

Stockholders' Equity

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Stockholders' Equity

Note 6 – Stockholders’ Equity

The Company is authorized to issue 5,000,000 shares of preferred stock as of March 31, 2020 and December 31, 2019, respectively. As of March 31, 2020 and December 31, 2019, no shares of preferred stock were issued and outstanding. The Company is authorized to issue 100,000,000 shares of common stock as of March 31, 2020 and December 31, 2019, respectively.

Sale of Common Stock and Pre-Funded Warrants

In December 2017, the Company filed a registration statement on Form S-3 with the SEC using a “shelf” registration statement, file No. 333-222366, which became effective January 10, 2018 (the Registration Statement). Under this shelf registration process, the Company may from time to time sell any combination of the securities described in the Registration Statement in one or more offerings up to an aggregate offering price of $250.0 million. In connection with the filing of this Registration Statement, the Company entered into a sales agreement under which the Company may offer and sell shares of its common stock having an aggregate offering price of up to $75.0 million through “at the market offerings” (ATM). As of March 31, 2020, no shares have been sold under the ATM program and $21.4 million remains available for sale under this Registration Statement.

In December 2019, the Company sold to various investors an aggregate of 6,287,878 shares of common stock at a public offering price of $16.50 per share, which included the exercise in full by the underwriters of their option to purchase 1,136,363 additional shares of common stock, and pre-funded warrants to purchase 2,424,242 shares of common stock at a public offering price of $16.499 per warrant. The Company received aggregate net proceeds of $134.7 million from the offering and the option exercise, after deducting underwriting discounts and commissions and offering expenses payable by the Company. The pre-funded warrants are exercisable immediately upon issuance at an exercise price of $0.001 per share. Per their terms, the outstanding pre-funded warrants to purchase shares of the Company’s common stock generally may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99% following such exercise. The exercise price and number of shares of common stock issuable upon the exercise of the pre-funded warrants (Warrant Shares) are subject to adjustment in the event of any stock dividends and splits, reverse stock split, recapitalization, reorganization or similar transaction, as described in the pre-funded warrant agreements. Under certain circumstances, the pre-funded warrants may be exercisable on a “cashless” basis. Both the pre-funded warrants and the Warrant Shares are registered securities.

The pre-funded warrants were classified as a component of permanent stockholders’ equity within additional paid-in-capital and were recorded at the issuance date using a relative fair value allocation method. The pre-funded warrants are equity classified because they are freestanding financial instruments that are legally detachable and separately exercisable from the equity instruments, are immediately exercisable, do not embody an obligation for the Company to repurchase its shares, permit the holders to receive a fixed number of common shares upon exercise, are indexed to the Company’s common stock and meet the equity classification criteria. In addition, such pre-funded warrants do not provide any guarantee of value or return. The Company valued the pre-funded warrants at issuance, concluding their sales price approximated their fair value, and allocated net proceeds from the sale proportionately to the common stock and pre-funded warrants of which $37.5 million was allocated to the pre-funded warrants and recorded as a component of additional paid-in-capital.

Common Stock Warrants

As of, March 31, 2020 and December 31, 2019 the following warrants to purchase shares of the Company’s common stock were issued and outstanding:

Issue date	Expiration date	Exercise Price per Share		Number of warrants outstanding
September 10, 2010	September 10, 2020	$	30.000		15,296
December 16, 2019	None	$	0.001		2,424,242
					2,439,538

There were no warrants exercised during the three months ended March 31, 2020 or 2019.

Stock Plans and Stock-Based Compensation

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Plans and Stock-Based Compensation

Note 7 – Stock Plans and Stock-Based Compensation

Equity Incentive Plans

In May 2018, the Company’s stockholders approved (1) 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 (2) the Assembly Biosciences Inc. Employee Stock Purchase Plan (the 2018 ESPP) pursuant to which the Company reserved 400,000 shares of its common stock for issuance in connection with purchases by employees pursuant to this plan.

In May 2019, the Company’s stockholders approved an amendment to the 2018 Plan that increased the aggregate shares of common stock reserved under the 2018 Plan to 3,000,000.

As of March 31, 2020, 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 March 31, 2020, the Company also had awards outstanding under the Assembly Biosciences, Inc. 2017 Inducement Award Plan (the 2017 Plan), the Assembly Biosciences, Inc. 2019 Inducement Award Plan (the 2019 Plan) and the Assembly Biosciences, Inc. 2020 Inducement Award Plan (the 2020 Plan).

The Company issues new shares of common stock to settle options exercised and 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 three months ended March 31, 2020 is as follows:

	Number of Shares			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (Years)		Total Intrinsic Value (in thousands)
Outstanding as of December 31, 2019		5,613,353		$	15.90
Granted		833,140			14.76
Exercised		(16,834	)		7.05
Forfeited		(59,263	)		26.35
Outstanding as of March 31, 2020		6,370,396		$	15.67		7.4	$	21,547
Options vested and exercisable as of March 31, 2020		3,302,792		$	13.87		5.6	$	18,722

The weighted-average grant-date fair value of options granted was $9.74 and $13.71 during the three months ended March 31, 2020 and 2019, respectively. The total intrinsic value of options exercised during the three months ended March 31, 2020 and 2019 was $0.2 million and $0.3 million, respectively.

RSUs

A summary of the Company’s RSUs and related information for the three months ended March 31, 2020 is as follows:

	Number of RSU's				Weighted Average Fair Value Per RSU at Grant Price
Nonvested as of December 31, 2019		758,718			$	25.47
Granted		485,664				15.91
Vested		(94,224	)			34.55
Forfeited		(23,982	)			26.50
Nonvested as of March 31, 2020		1,126,176		⁽¹⁾	$	20.56

⁽¹⁾	Includes 126,250 RSUs that have vested but are subject to deferred settlement, which have a weighted average remaining contractual term of 2.3 years.

The total fair value of RSUs vested and settled during the three months ended March 31, 2020 and 2019 as $2.4 million and $2.2 million, respectively. The total intrinsic value of RSUs vested and settled during the three months ended March 31, 2020 and 2019 was $1.5 million and $1.3 million, respectively.

As of March 31, 2020, RSUs outstanding include 45,000 RSUs granted in December 2017 and 100,000 RSUs granted in September 2019 to executives of the Company, each with performance-based conditions. The total fair value of these awards is $0.7 million and $1.2 million, respectively. The performance conditions upon which these awards will vest are not yet deemed probable of being met, and accordingly no compensation expense has been recognized as of March 31, 2020 for these awards.

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 March 31,
	2020	2019
Exercise price	$14.45 - $19.13	$19.69 - $23.04
Expected volatility	66.38% - 82.23%	75.0% - 83.2%
Risk-free rate	0.46% - 1.44%	2.24% - 2.65%
Expected term (years)	5.5 - 7.0	5.5 - 7.0
Expected dividend yield	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.

The fair value of ESPP purchase rights were not material for any period presented.

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 (in thousands):

	Three Months Ended March 31,
	2020		2019
Research and development	$	1,945	$	2,728
General and administrative		2,979		3,849
Total stock-based compensation expense	$	4,924	$	6,577

As of March 31, 2020, there was $34.5 million of total unrecognized stock-based compensation related to outstanding equity awards which is expected to be recognized over a weighted average remaining amortization period of 1.8 years.

Collaboration Agreement

3 Months Ended

Mar. 31, 2020

Collaboration Agreement [Abstract]

Collaboration Agreement

Note 8 - 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 to 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).

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 $631.0 million related to seven development milestones and up to $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 90 days’ (prior to the initiation of the first POC trial of a licensed product) or 120 days’ (after the initiation of the first POC trial of a licensed product), as applicable, 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 the contract 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) grant 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 grant 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 which is currently estimated to occur in 2025. 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 three months ended March 31, 2020 and 2019, the Company recognized $4.1 million and $3.9 million, respectively, in revenue associated with the Collaboration Agreement. Short-term and long-term deferred revenue contract liabilities related to the Collaboration Agreement were $6.7 million and $29.3 million at March 31, 2020 and $6.4 million and $30.6 million at December 31, 2019.

On the unaudited condensed consolidated balance sheets, contract asset balances of $3.1 million and $3.4 million were recorded as accounts receivable from collaboration as of March 31, 2020 and December 31, 2019, 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
Three Months Ended March 31, 2020
Contract liabilities:
Deferred revenue	$	37,048	$	—	$	(1,007	)	$	36,041

	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Three Months Ended March 31, 2019
Contract liabilities:
Deferred revenue	$	40,660	$	—	$	(859	)	$	39,801

	Three Months Ended March 31,
	2020		2019
Collaboration revenue recognized in the period from
Amounts included in deferred revenue at the beginning of the period	$	1,007	$	859
Performance obligations satisfied in previous period		—		—

Milestones and Research Agreements

3 Months Ended

Mar. 31, 2020

Milestones And Research Agreements [Abstract]

Milestones and Research Agreements

Note 9 - 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 $0.8 million, with a portion related to the first performance milestone having been paid. The Company is obligated to pay IURTC royalty payments based on net sales of the licensed technology. The Company is also required to pay diligence maintenance fees each year to the extent that the royalty, sublicensing, and milestone payments to IURTC are less than such fees for that year. Amounts paid in the three months ended March 31, 2020 and 2019 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. In addition, the Company must pay Therabiome lesser amounts for foreign regulatory milestones, which vary by country and region. The Company is also required to 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 such 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.

No amounts were accrued for this agreement as of and for the three months ended March 31, 2020. A regulatory milestone was determined to have occurred and $0.1 million was paid under this agreement as of and during the three months ended March 31, 2019.

Leases

3 Months Ended

Mar. 31, 2020

Lease Cost [Abstract]

Leases

Note 10 - Leases

Operating Leases

The Company leases office space for corporate, administrative and laboratory functions in South San Francisco, California under a sub-sublease that expires in December 2023. The Company also leases office space in Carmel, Indiana under a lease agreement that expires in August 2023 as well as office and laboratory space in Groton, Connecticut under a lease that expires in March 2021. The Company’s China subsidiary leases office space in Shanghai that expires in May 2021 and rents lab space in Shanghai under a lease agreement that expires in December 2020. Additionally, the Company’s China subsidiary leases office space in Beijing under a lease agreement that expires in December 2020. 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. Certain equipment leases continue to expire in 2020, with the final lease expiring in 2022.

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 March 31, 2020, the Company had operating lease liabilities of $11.8 million and ROU assets of $11.5 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 March 31, 2020		Three Months Ended March 31, 2019
Lease cost
Operating lease cost	$	1,151	$	1,091
Short-term lease cost		100		321
Variable lease cost		284		299
Total lease cost	$	1,535	$	1,711

Three Months Ended

March 31, 2020

Three Months Ended

March 31, 2019

Operating cash flows from operating leases

1,120

1,037

ROU assets exchanged for new operating lease liabilities

362

13,933

As of March 31, 2020 and December 31, 2019, the weighted-average remaining lease term for operating leases was 3.4 years and 2.7 years, respectively. As of both March 31, 2020 and December 31, 2019, the weighted-average discount rate for operating leases was 9.4%.

As of March 31, 2020, the maturities of the Company’s operating lease liabilities were as follows (in thousands):

Nine months ended December 31, 2020	$	3,510
Year Ended December 31, 2021		3,924
Year Ended December 31, 2022		3,560
Year Ended December 31, 2023		3,303
Total		14,297
Less: present value discount		(2,494	)
Operating lease liabilities	$	11,803

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Other Risks and Uncertainties

Income Taxes

Net Loss per Share

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 March 31,
	2020			2019
Numerator:
Net loss		(26,655	)		(27,052	)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share		35,079,756			25,668,798
Net (loss) income per share:
Basic		(0.76	)		(1.05	)
Diluted		(0.76	)		(1.05	)

	Three Months Ended March 31,
	2020		2019
Warrants to purchase common stock		15,296		15,296
Options to purchase common stock		6,370,396		5,111,590
Common stock subject to purchase under our ESPP		32,940		22,432
Unvested RSUs		999,926		607,656
Total		7,418,558		5,756,974

Recent Accounting Pronouncements

Adoption of Recent Accounting Pronouncements

Recent Accounting Pronouncements

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 20
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 740
-Section 50
-Paragraph 1
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 235
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32809-109319

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=116657188&loc=SL116659661-227067

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32840-109319

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=116821951&loc=d3e32247-109318

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=116821951&loc=d3e32280-109318

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section 05
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-URI http://asc.fasb.org/extlink&oid=65884525&loc=d3e40913-109327

+ Details

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

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 March 31,
	2020			2019
Numerator:
Net loss		(26,655	)		(27,052	)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share		35,079,756			25,668,798
Net (loss) income per share:
Basic		(0.76	)		(1.05	)
Diluted		(0.76	)		(1.05	)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

	Three Months Ended March 31,
	2020		2019
Warrants to purchase common stock		15,296		15,296
Options to purchase common stock		6,370,396		5,111,590
Common stock subject to purchase under our ESPP		32,940		22,432
Unvested RSUs		999,926		607,656
Total		7,418,558		5,756,974

Investments in Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2020

Investments Debt And Equity Securities [Abstract]

Schedule of Investments in Marketable Securities

Investments in marketable securities consisted of the following (in thousands):

	March 31, 2020
	Amortized Cost		Gross Unrealized Gain ⁽¹⁾		Gross Unrealized Loss ⁽¹⁾			Fair Value
Cash equivalents
Money market funds	$	39,010	$	—	$	—		$	39,010
Total cash equivalents		39,010		—		—			39,010
Short-term investments
U.S. and foreign corporate debt securities		63,354		10		(121	)		63,243
Asset-backed securities		34,893		9		(44	)		34,858
U.S. treasury securities		44,637		368		—			45,005
U.S. and foreign commercial paper		63,697		—		—			63,697
Total short-term investments		206,581		387		(165	)		206,803
Total cash equivalents and investments	$	245,591	$	387	$	(165	)	$	245,813

(1)	Gross unrealized gain (loss) is pre-tax.

	December 31, 2019
	Amortized Cost		Gross Unrealized Gain ⁽¹⁾		Gross Unrealized Loss ⁽¹⁾			Fair Value
Cash equivalents
Money market funds	$	33,095	$	—	$	—		$	33,095
U.S. and foreign corporate debt securities		5,000		—		(1	)		4,999
U.S. and foreign commercial paper		4,484		—		—			4,484
Total cash equivalents		42,579		—		(1	)		42,578
Short-term investments
U.S. and foreign corporate debt securities		72,452		38		(4	)		72,486
Asset-backed securities		34,008		17		—			34,025
U.S. treasury securities		44,692		24		(2	)		44,714
U.S. and foreign commercial paper		76,086		—		—			76,086
Total short-term investments		227,238		79		(6	)		227,311
Total cash equivalents and investments	$	269,817	$	79	$	(7	)	$	269,889

(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 (in thousands):

	March 31, 2020
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	39,010	$	—	$	—	$	39,010
Total cash equivalents		39,010		—		—		39,010
Short-term investments
U.S. and foreign corporate debt securities		—		63,243		—		63,243
Asset-backed securities		—		34,858		—		34,858
U.S. treasury securities		—		45,005		—		45,005
U.S. and foreign commercial paper		—		63,697		—		63,697
Total short-term investments		—		206,803		—		206,803
Total assets measured at fair value	$	39,010	$	206,803	$	—	$	245,813

	December 31, 2019
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund		33,095		—		—		33,095
U.S and foreign corporate debt securities		—		4,999		—		4,999
U.S and foreign commercial paper		—		4,484		—		4,484
Total cash equivalents		33,095		9,483		—		42,578
Short-term investments
U.S. and foreign corporate debt securities		—		72,486		—		72,486
Asset-backed securities		—		34,025		—		34,025
U.S. treasury securities		—		44,714		—		44,714
U.S. and foreign commercial paper		—		76,086		—		76,086
Total short-term investments		—		227,311		—		227,311
Total assets measured at fair value	$	33,095	$	236,794	$	—	$	269,889

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Property and Equipment, Net (Tables)

3 Months Ended

Mar. 31, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consist of the following (in thousands):

	Useful life	March 31,			December 31,
	(Years)	2020			2019
Lab equipment	3 to 5	$	286		$	247
Office equipment	7		699			699
Leasehold improvement	1 to 5		2,084			2,084
Total property and equipment			3,069			3,030
Less: Accumulated depreciation and amortization			(1,315	)		(1,200	)
Construction in progress	N/A		26			-
Property and equipment, net		$	1,780		$	1,830

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following (in thousands):

	March 31,		December 31,
	2020		2019
Accrued expenses:
Accrued compensation	$	2,144	$	5,312
Accrued restructuring charges		1,627		2,094
Accrued professional fees and other		659		880
Total accrued expenses	$	4,430	$	8,286

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Summary of Warrants to Purchase Shares of Company's Common Stock

As of, March 31, 2020 and December 31, 2019 the following warrants to purchase shares of the Company’s common stock were issued and outstanding:

Issue date	Expiration date	Exercise Price per Share		Number of warrants outstanding
September 10, 2010	September 10, 2020	$	30.000		15,296
December 16, 2019	None	$	0.001		2,424,242
					2,439,538

Stock Plans and Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

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 three months ended March 31, 2020 is as follows:

	Number of Shares			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (Years)		Total Intrinsic Value (in thousands)
Outstanding as of December 31, 2019		5,613,353		$	15.90
Granted		833,140			14.76
Exercised		(16,834	)		7.05
Forfeited		(59,263	)		26.35
Outstanding as of March 31, 2020		6,370,396		$	15.67		7.4	$	21,547
Options vested and exercisable as of March 31, 2020		3,302,792		$	13.87		5.6	$	18,722

Schedule of RSU's and Related Information

A summary of the Company’s RSUs and related information for the three months ended March 31, 2020 is as follows:

	Number of RSU's				Weighted Average Fair Value Per RSU at Grant Price
Nonvested as of December 31, 2019		758,718			$	25.47
Granted		485,664				15.91
Vested		(94,224	)			34.55
Forfeited		(23,982	)			26.50
Nonvested as of March 31, 2020		1,126,176		⁽¹⁾	$	20.56

⁽¹⁾	Includes 126,250 RSUs that have vested but are subject to deferred settlement, which have a weighted average remaining contractual term of 2.3 years.

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 March 31,
	2020	2019
Exercise price	$14.45 - $19.13	$19.69 - $23.04
Expected volatility	66.38% - 82.23%	75.0% - 83.2%
Risk-free rate	0.46% - 1.44%	2.24% - 2.65%
Expected term (years)	5.5 - 7.0	5.5 - 7.0
Expected dividend yield	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 (in thousands):

	Three Months Ended March 31,
	2020		2019
Research and development	$	1,945	$	2,728
General and administrative		2,979		3,849
Total stock-based compensation expense	$	4,924	$	6,577

Collaboration Agreement (Tables)

3 Months Ended

Mar. 31, 2020

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
Three Months Ended March 31, 2020
Contract liabilities:
Deferred revenue	$	37,048	$	—	$	(1,007	)	$	36,041

	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Three Months Ended March 31, 2019
Contract liabilities:
Deferred revenue	$	40,660	$	—	$	(859	)	$	39,801

Schedule of Collaboration Revenue Recognized with the Period

	Three Months Ended March 31,
	2020		2019
Collaboration revenue recognized in the period from
Amounts included in deferred revenue at the beginning of the period	$	1,007	$	859
Performance obligations satisfied in previous period		—		—

Leases (Tables)

3 Months Ended

Mar. 31, 2020

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 March 31, 2020		Three Months Ended March 31, 2019
Lease cost
Operating lease cost	$	1,151	$	1,091
Short-term lease cost		100		321
Variable lease cost		284		299
Total lease cost	$	1,535	$	1,711

Three Months Ended

March 31, 2020

Three Months Ended

March 31, 2019

Operating cash flows from operating leases

1,120

1,037

ROU assets exchanged for new operating lease liabilities

362

13,933

Schedule of Maturities Operating Lease Liabilities

As of March 31, 2020, the maturities of the Company’s operating lease liabilities were as follows (in thousands):

Nine months ended December 31, 2020	$	3,510
Year Ended December 31, 2021		3,924
Year Ended December 31, 2022		3,560
Year Ended December 31, 2023		3,303
Total		14,297
Less: present value discount		(2,494	)
Operating lease liabilities	$	11,803

Nature of Business - Additional Information (Details)	3 Months Ended
Nature of Business - Additional Information (Details)	Mar. 31, 2020 segment product
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Operating segments (in segments) \| segment	1
FDA approved products (in products) \| product	0

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details) - Public Offering	1 Months Ended
	Dec. 31, 2019 $ / shares shares
Significant Accounting Policies [Line Items]
Number of shares sold	6,287,878
Number of pre-funded warrants sold to purchase of common stock	2,424,242
Pre-funded warrants exercisable price per share \| $ / shares	$ 0.001
Common Stock
Significant Accounting Policies [Line Items]
Number of shares sold	6,287,878

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net loss	$ (26,655)	$ (27,052)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share	35,079,756	25,668,798
Net (loss) income per share:
Basic	$ (0.76)	$ (1.05)
Diluted	$ (0.76)	$ (1.05)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

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+ Details

- Definition

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

+ References + Details

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	7,418,558	5,756,974
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)	6,370,396	5,111,590
Common stock subject to purchase under ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	32,940	22,432
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	999,926	607,656

Investments in Marketable Securities - Schedule of Investments in Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investments in marketable securities:
Amortized Cost	$ 42,326	$ 46,732
Fair Value	206,803	227,311
Amortized Cost	245,591	269,817
Gross Unrealized Gain	387	79
Gross Unrealized Loss	(165)	(7)
Fair Value	245,813	269,889
Cash equivalents
Investments in marketable securities:
Amortized Cost	39,010	42,579
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	(1)
Fair Value	39,010	42,578
Cash equivalents \| Money market fund
Investments in marketable securities:
Amortized Cost	39,010	33,095
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	39,010	33,095
Short-term investments
Investments in marketable securities:
Amortized Cost	206,581	227,238
Gross Unrealized Gain	387	79
Gross Unrealized Loss	(165)	(6)
Fair Value	206,803	227,311
U.S and foreign corporate debt securities \| Cash equivalents
Investments in marketable securities:
Amortized Cost		5,000
Gross Unrealized Gain		0
Gross Unrealized Loss		(1)
Fair Value		4,999
U.S and foreign corporate debt securities \| Short-term investments
Investments in marketable securities:
Amortized Cost	63,354	72,452
Gross Unrealized Gain	10	38
Gross Unrealized Loss	(121)	(4)
Fair Value	63,243	72,486
Asset-backed securities \| Short-term investments
Investments in marketable securities:
Amortized Cost	34,893	34,008
Gross Unrealized Gain	9	17
Gross Unrealized Loss	(44)	0
Fair Value	34,858	34,025
U.S. treasury securities \| Short-term investments
Investments in marketable securities:
Amortized Cost	44,637	44,692
Gross Unrealized Gain	368	24
Gross Unrealized Loss	0	(2)
Fair Value	45,005	44,714
U.S. and foreign commercial paper \| Cash equivalents
Investments in marketable securities:
Amortized Cost		4,484
Gross Unrealized Gain		0
Gross Unrealized Loss		0
Fair Value		4,484
U.S. and foreign commercial paper \| Short-term investments
Investments in marketable securities:
Amortized Cost	63,697	76,086
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	$ 63,697	$ 76,086

Investments in Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
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 Securities - Schedule of Fair Value of Financial Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Short-term investments
Short-term investments	$ 206,803	$ 227,311
Recurring
Cash equivalents
Cash equivalents	39,010	42,578
Short-term investments
Short-term investments	206,803	227,311
Total assets measured at fair value	245,813	269,889
Recurring \| U.S and foreign corporate debt securities
Cash equivalents
Cash equivalents		4,999
Short-term investments
Short-term investments	63,243	72,486
Recurring \| Asset-backed securities
Short-term investments
Short-term investments	34,858	34,025
Recurring \| U.S. treasury securities
Short-term investments
Short-term investments	45,005	44,714
Recurring \| U.S. and foreign commercial paper
Cash equivalents
Cash equivalents		4,484
Short-term investments
Short-term investments	63,697	76,086
Recurring \| Money market fund
Cash equivalents
Cash equivalents	39,010	33,095
Recurring \| Level 1
Cash equivalents
Cash equivalents	39,010	33,095
Short-term investments
Short-term investments	0	0
Total assets measured at fair value	39,010	33,095
Recurring \| Level 1 \| U.S and foreign corporate debt securities
Cash equivalents
Cash equivalents		0
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
Cash equivalents
Cash equivalents		0
Short-term investments
Short-term investments	0	0
Recurring \| Level 1 \| Money market fund
Cash equivalents
Cash equivalents	39,010	33,095
Recurring \| Level 2
Cash equivalents
Cash equivalents	0	9,483
Short-term investments
Short-term investments	206,803	227,311
Total assets measured at fair value	206,803	236,794
Recurring \| Level 2 \| U.S and foreign corporate debt securities
Cash equivalents
Cash equivalents		4,999
Short-term investments
Short-term investments	63,243	72,486
Recurring \| Level 2 \| Asset-backed securities
Short-term investments
Short-term investments	34,858	34,025
Recurring \| Level 2 \| U.S. treasury securities
Short-term investments
Short-term investments	45,005	44,714
Recurring \| Level 2 \| U.S. and foreign commercial paper
Cash equivalents
Cash equivalents		4,484
Short-term investments
Short-term investments	63,697	76,086
Recurring \| Level 2 \| Money market fund
Cash equivalents
Cash equivalents	0	0
Recurring \| Level 3
Cash equivalents
Cash equivalents	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
Cash equivalents
Cash equivalents		0
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
Cash equivalents
Cash equivalents		0
Short-term investments
Short-term investments	0	0
Recurring \| Level 3 \| Money market fund
Cash equivalents
Cash equivalents	$ 0	$ 0

Property and Equipment, Net - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment
Total property and equipment	$ 3,069	$ 3,030
Less: Accumulated depreciation and amortization	(1,315)	(1,200)
Property and equipment, net	1,780	1,830
Lab equipment
Property, Plant and Equipment
Total property and equipment	$ 286	247
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 and equipment	$ 699	699
Useful Life (in years)	7 years
Leasehold improvement
Property, Plant and Equipment
Total property and equipment	$ 2,084	$ 2,084
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 and equipment	$ 26

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation	$ 0.1	$ 0.1

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued expenses:
Accrued compensation	$ 2,144	$ 5,312
Accrued restructuring charges	1,627	2,094
Accrued professional fees and other	659	880
Total accrued expenses	$ 4,430	$ 8,286

Accrued Expenses - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued restructuring charges	$ 1,627	$ 2,094

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2017
Subsidiary Sale Of Stock [Line Items]
Preferred stock, shares authorized	5,000,000	5,000,000
Common stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Initial public offering value of shares authorized				$ 250.0
Common stock remains available for sale		$ 21.4
Warrants exercisable description		Per their terms, the outstanding pre-funded warrants to purchase shares of the Company’s common stock generally may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99% following such exercise.
Proceeds from sale of pre-funded warrants	$ 37.5
Number of warrants exercised		0	0
Maximum
Subsidiary Sale Of Stock [Line Items]
Ownership percentage to exercise warrant	19.99%
At the Market Offerings
Subsidiary Sale Of Stock [Line Items]
Number of shares sold		0
At the Market Offerings \| Maximum
Subsidiary Sale Of Stock [Line Items]
Initial public offering value of shares authorized				$ 75.0
Public Offering
Subsidiary Sale Of Stock [Line Items]
Number of shares sold	6,287,878
Sale of stock, price per share	$ 16.50
Number of pre-funded warrants sold to purchase of common stock	2,424,242
Sale of stock, price per warrant	$ 16.499
Net proceeds from the issuance of common stock through equity plans	$ 134.7
Pre-funded warrants exercisable price per share	$ 0.001
Underwriters
Subsidiary Sale Of Stock [Line Items]
Number of shares sold	1,136,363

Stockholders' Equity - Summary of Warrants to Purchase Shares of Company's Common Stock (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Subsidiary Sale Of Stock [Line Items]
Number of warrants outstanding	2,439,538	2,439,538
Warrants Issued on September 10, 2010
Subsidiary Sale Of Stock [Line Items]
Issue date	Sep. 10, 2010	Sep. 10, 2010
Expiration date	Sep. 10, 2020	Sep. 10, 2020
Exercise Price per Share	$ 30.000	$ 30.000
Number of warrants outstanding	15,296	15,296
Warrants Issued on December 16, 2019
Subsidiary Sale Of Stock [Line Items]
Issue date	Dec. 16, 2019	Dec. 16, 2019
Exercise Price per Share	$ 0.001	$ 0.001
Number of warrants outstanding	2,424,242	2,424,242

Stock Plans and Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended
	Sep. 30, 2019	Dec. 31, 2017	Mar. 31, 2020	Mar. 31, 2019	May 31, 2019	May 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Shares reserved for issuance (in shares)					3,000,000	1,900,000
Stock-based compensation			$ 4,924,000	$ 6,577,000
Unrecognized stock-based compensation expense			$ 34,500,000
Unrecognized stock-based compensation expense expected to be recognized, term			1 year 9 months 18 days
Weighted-average grant-date fair value of options granted			$ 9.74	$ 13.71
Total intrinsic value of options exercised			$ 200,000	$ 300,000
RSUs
Share-based Compensation Arrangement by Share-based Payment Award
Total fair value of awards vested and settled			2,400,000	2,200,000
Total intrinsic value of awards vested and settled			$ 1,500,000	$ 1,300,000
Granted			485,664
RSUs \| Executives
Share-based Compensation Arrangement by Share-based Payment Award
Granted	100,000	45,000
Total fair value of awards	$ 1,200,000	$ 700,000
Stock-based compensation			$ 0
2018 ESPP
Share-based Compensation Arrangement by Share-based Payment Award
Number of common shares reserved for future issuance			400,000

Stock Plans and Stock-Based Compensation - Schedule of Stock Options Activity (Details) - Options $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) $ / shares shares
Number of Shares
Options, Outstanding at beginning of period \| shares	5,613,353
Option, Granted \| shares	833,140
Option, Exercised \| shares	(16,834)
Option, Forfeited \| shares	(59,263)
Option, Outstanding at end of period \| shares	6,370,396
Options vested and exercisable \| shares	3,302,792
Weighted Average Exercise Price Per Share
Options, Outstanding at beginning of period \| $ / shares	$ 15.90
Option, Granted \| $ / shares	14.76
Option, Exercised \| $ / shares	7.05
Option, Forfeited \| $ / shares	26.35
Option, Outstanding at end of period \| $ / shares	15.67
Options vested and exercisable \| $ / shares	$ 13.87
Options Outstanding, Weighted Average Remaining Contractual Term (Years)	7 years 4 months 24 days
Options Exercisable, Weighted Average Remaining Contractual Term (Years)	5 years 7 months 6 days
Total Intrinsic Value
Option, Outstanding at end of period \| $	$ 21,547
Options vested and exercisable \| $	$ 18,722

Stock Plans and Stock-Based Compensation - Schedule of RSU's and Related Information (Details) - RSUs	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Number of Shares
Beginning of period \| shares	758,718
Granted \| shares	485,664
Vested \| shares	(94,224)
Forfeited \| shares	(23,982)
Ending of period \| shares	1,126,176
Weighted Average Fair Value Per RSU at Grant Price
Beginning of period \| $ / shares	$ 25.47
Granted \| $ / shares	15.91
Vested \| $ / shares	34.55
Forfeited \| $ / shares	26.50
Ending of period \| $ / shares	$ 20.56

Stock Plans and Stock-Based Compensation - Schedule of RSU's and Related Information (Parenthetical) (Details) - RSUs	3 Months Ended
	Mar. 31, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award
Vested and subject to deferred settlement	126,250
Weighted average remaining contractual term subject to deferred settlement	2 years 3 months 18 days

Stock Plans and Stock-Based Compensation - Assumptions for Weighted Average Fair Value of Options Granted (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award
Expected dividend yield	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price	$ 14.45	$ 19.69
Expected volatility	66.38%	75.00%
Risk-free rate	0.46%	2.24%
Expected term (years)	5 years 6 months	5 years 6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price	$ 19.13	$ 23.04
Expected volatility	82.23%	83.20%
Risk-free rate	1.44%	2.65%
Expected term (years)	7 years	7 years

Stock Plans and Stock-Based Compensation -Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Compensation expense:
Total stock-based compensation expense	$ 4,924	$ 6,577
Research and Development
Compensation expense:
Total stock-based compensation expense	1,945	2,728
General and administrative
Compensation expense:
Total stock-based compensation expense	$ 2,979	$ 3,849

Collaboration Agreement - Additional Information (Details) $ in Thousands		3 Months Ended
	Feb. 10, 2017 USD ($)	Mar. 31, 2020 USD ($) Milestone	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Collaboration Agreements:
Collaboration revenue		$ 4,081	$ 3,885
Contract with customer, liability, current		6,715		$ 6,411
Contract with customer, liability, noncurrent		29,326		30,637
Accounts receivable from collaboration		3,055		3,374
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		4,100	$ 3,900
Contract with customer, liability, current		6,700		6,400
Contract with customer, liability, noncurrent		29,300		$ 30,600
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 - Schedule of Changes in Contract Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Collaboration Agreement [Abstract]
Balance at Beginning of Period	$ 37,048	$ 40,660
Additions	0	0
Deductions	(1,007)	(859)
Balance at End of Period	$ 36,041	$ 39,801

Collaboration Agreement - Schedule of Collaboration Revenue Recognized with the Period (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Collaboration revenue recognized in the period from
Amounts included in deferred revenue at the beginning of the period	$ 1,007	$ 859
Performance obligations satisfied in previous period	$ 0	$ 0

Milestones and Research Agreements - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Milestone and Research Agreements:
Potential milestone payment	$ 800
Accrued expenses	4,430	$ 8,286
License Agreement Terms
Milestone and Research Agreements:
Accrued expenses	0
Regulatory milestone payment	$ 100

Leases - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease, liability	$ 11,803
Operating lease, ROU assets	$ 11,479	$ 11,975
Weighted-average remaining lease term - operating leases	3 years 4 months 24 days	2 years 8 months 12 days
Weighted-average discount rate - operating leases	9.40%	9.40%

Leases - Schedule of Quantitative Information of Operating Leases (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lease cost
Operating lease cost	$ 1,151	$ 1,091
Short-term lease cost	100	321
Variable lease cost	284	299
Total lease cost	1,535	1,711
Operating cash flows from operating leases	1,120	1,037
Operating lease liabilities arising from obtaining ROU assets	$ 362	$ 13,933

Leases - Schedule of Maturities Operating Lease Liabilities (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Lease Cost [Abstract]
Nine months ended December 31, 2020	$ 3,510
Year Ended December 31, 2021	3,924
Year Ended December 31, 2022	3,560
Year Ended December 31, 2023	3,303
Total	14,297
Less: present value discount	(2,494)
Operating lease liabilities	$ 11,803