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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	May 06, 2019
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Entity Registrant Name	ASSEMBLY BIOSCIENCES, INC.
Entity Central Index Key	0001426800
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Trading Symbol	ASMB
Entity Common Stock, Shares Outstanding		25,600,979
Entity Emerging Growth Company	false
Entity Small Business	false

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 29,107	$ 41,471
Marketable securities	164,429	176,609
Accounts receivable from collaboration	2,987	2,430
Prepaid expenses and other current assets	4,283	1,992
Total current assets	200,806	222,502
Long-term assets
Property and equipment, net	2,079	557
Operating lease right-of-use assets	13,063	0
Other assets	1,661	3,348
Indefinite-lived intangible asset	29,000	29,000
Goodwill	12,638	12,638
Total assets	259,247	268,045
Current liabilities
Accounts payable	2,427	3,693
Accrued expenses	10,141	9,679
Deferred revenue - short-term	9,933	5,100
Operating lease liabilities - short-term	2,704	0
Total current liabilities	25,205	18,472
Long-term liabilities
Deferred rent	0	108
Deferred tax liabilities	3,252	3,252
Deferred revenue - long-term	29,868	35,560
Operating lease liabilities - long-term	10,521	0
Total liabilities	68,846	57,392
Commitments and contingencies
Stockholders' equity
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding	0	0
Common stock, $0.001 par value; 100,000,000 shares authorized as of March 31, 2019 and December 31, 2018; 25,549,757 and 25,495,425 shares issued and outstanding as of March 31, 2019 and December 31, 2018, respectively	26	25
Additional paid-in capital	559,453	552,762
Accumulated other comprehensive loss	(239)	(347)
Accumulated deficit	(368,839)	(341,787)
Total stockholders' equity	190,401	210,653
Total liabilities and stockholders' equity	$ 259,247	$ 268,045

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	25,549,757	25,495,425
Common stock, shares outstanding	25,549,757	25,495,425

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Collaboration revenue	$ 3,885	$ 3,565
Operating expenses:
Research and development	22,704	14,541
General and administrative	9,517	5,696
Total operating expenses	32,221	20,237
Loss from operations	(28,336)	(16,672)
Other income (expenses)
Interest and other income	1,276	446
Other income (expense), net	1	(23)
Total other income	1,277	423
Loss before income taxes	(27,059)	(16,249)
Income tax benefit	7	0
Net loss	(27,052)	(16,249)
Other comprehensive (loss) income
Unrealized gain (loss) on marketable securities, net of tax	108	(67)
Comprehensive loss	$ (26,944)	$ (16,316)
Net loss per share, basic and diluted	$ (1.05)	$ (0.80)
Weighted average common shares outstanding, basic and diluted	25,668,798	20,231,804

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net loss	$ (27,052)	$ (16,249)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	135	168
Stock-based compensation	6,577	4,083
Net accretion and amortization of investments in marketable securities	(592)	0
Non-cash rent expense	1,091	0
Deferred income tax benefit	(7)	0
Loss on disposal of fixed assets	102	0
Other	(1)	23
Changes in operating assets and liabilities:
Accounts receivable from collaboration	(557)	10
Prepaid expenses and other current assets	(2,558)	(906)
Other assets	1,687	0
Accounts payable	(1,266)	249
Accrued expenses	398	(1,491)
Deferred revenue	(859)	(1,301)
Deferred rent	0	(86)
Operating lease liabilities	(1,037)	0
Net cash used in operating activities	(23,939)	(15,500)
Cash flows from investing activities
Purchases of property and equipment	(1,488)	(39)
Purchases of marketable securities	(49,030)	(13,032)
Proceeds from maturities of marketable securities	61,453	11,971
Proceeds from sale of marketable securities	500	0
Net cash provided by (used in) investing activities	11,435	(1,100)
Cash flows from financing activities
Proceeds from the exercise of stock options	140	1,494
Net cash provided by financing activities	140	1,494
Net decrease in cash and cash equivalents	(12,364)	(15,106)
Cash and cash equivalents at the beginning of the period	41,471	82,033
Cash and cash equivalents at the end of the period	$ 29,107	$ 66,927

CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 113,120	$ 20	$ 364,528	$ (392)	$ (251,036)
Balance (in shares) at Dec. 31, 2017		20,137,974
Proceeds from the exercise of stock options	1,494	$ 0	1,494	0	0
Proceeds from the exercise of stock options (in shares)		248,762
Unrealized gain (loss) on marketable securities	(67)	$ 0	0	(67)	0
Stock-based compensation	4,083	0	4,083	0	0
Net loss	(16,249)	0	0	0	(16,249)
Balance at Mar. 31, 2018	102,381	$ 20	370,105	(459)	(267,285)
Balance (in shares) at Mar. 31, 2018		20,386,736
Balance at Dec. 31, 2018	210,653	$ 25	552,762	(347)	(341,787)
Balance (in shares) at Dec. 31, 2018		25,495,425
Proceeds from the exercise of stock options	140	$ 0	140	0	0
Proceeds from the exercise of stock options (in shares)		21,000
Issuance of shares for settlement of restricted stock units	0	$ 1	(1)	0	0
Issuance of shares for settlement of restricted stock units (in shares)		33,332
Reclassification of stock-based awards from equity to accrued expenses	(4)	$ 0	(4)	0	0
Unrealized gain (loss) on marketable securities	108	0	0	108	0
Stock-based compensation	6,556	0	6,556	0	0
Net loss	(27,052)	0	0	0	(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

Nature of Business

3 Months Ended

Mar. 31, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of Business

Note 1 - Nature of Business

Overview

Assembly Biosciences, Inc., together with its subsidiaries (Assembly or the Company), incorporated in Delaware in October 2005, is a clinical-stage biotechnology company developing innovative therapeutics targeting hepatitis B virus (HBV) and diseases associated with the microbiome. The Company operates in one segment and is headquartered in Carmel, Indiana with operations in South San Francisco, California and Groton, Connecticut.

The Company’s HBV-cure program is pursuing multiple drug candidates that inhibit the HBV lifecycle and block the generation of covalently closed circular DNA (cccDNA), with the aim of increasing the current low cure rates for patients with HBV. Assembly has discovered multiple novel core inhibitors, which are small molecules that directly target and allosterically modify the HBV core (HBc) protein.

The Company’s Microbiome program consists of a fully integrated platform that includes a disease-targeted strain isolation, identification, characterization and selection process, methods for strain purification and growth under current Good Manufacturing Practice (cGMP) conditions, and 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 capabilities, the Company is exploring product candidates for multiple disease indications, including ulcerative colitis (UC), Crohn’s disease, irritable bowel syndrome (IBS), non-alcoholic steatohepatitis (NASH) and immuno-oncology, which indications the Company will pursue with Allergan Pharmaceuticals International Limited (Allergan) described herein to the extent covered by the Research, Development, Collaboration and License Agreement (the Collaboration Agreement) or pursue either internally or in collaboration with other partners to the extent outside the scope of the Collaboration Agreement (Note 8).

Liquidity

The Company has not derived any revenue from product sales to date and currently has no approved products. Once a product has been developed, it will need to be approved for sale by the U.S. Food and Drug Administration (FDA) or an applicable foreign regulatory agency. Since inception, the Company’s operations have been financed primarily through the sale of equity securities, the proceeds from the exercise of warrants and stock options, the issuance of debt and an upfront payment related to the Collaboration Agreement. The Company has incurred losses from operations since inception and expects to continue to incur substantial losses for the next several years as it continues its product development efforts. Management believes the Company currently has sufficient funds to meet its operating requirements for at least the next twelve months following the date that these unaudited condensed consolidated interim financial statements are issued. If the Company cannot generate significant cash from its operations, it intends to obtain any additional funding it requires through strategic relationships, public or private equity or debt financings, grants or other arrangements. The Company cannot assure such funding will be available on reasonable terms, if at all.

If the Company is unable to generate enough revenue from the Collaboration Agreement when needed or to secure additional sources of funding and receive related full and timely collections of amounts due, it may be necessary to significantly reduce the current rate of spending through reductions in staff and delaying, scaling back, or stopping certain research and development programs, including more costly clinical trials.

Summary of Significant Accounting Policies and Recent Accounting Pronouncements

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies and Recent Accounting Pronouncements

Note 2 - Summary of Significant Accounting Policies and Recent Accounting Pronouncements

Basis of Presentation

The accompanying unaudited interim condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and pursuant to the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the U.S. Securities and Exchange Commission (SEC) and on the same basis as the Company prepares its annual audited consolidated financial statements.

In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited 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 GAAP and should be read in conjunction with the Company’s financial statements and accompanying notes for the fiscal year ended December 31, 2018, which is contained in the Company’s Annual Report on Form 10-K as filed with the SEC on February 28, 2019. The results for the three months ended March 31, 2019 are not necessarily indicative of results to be expected for the entire year ending December 31, 2019 or future operating periods.

Use of Estimates

The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. Actual results could differ from those estimates.

Significant estimates inherent in the preparation of the accompanying unaudited condensed consolidated financial statements include recoverability and useful lives (indefinite or finite) of intangible assets, assessment of impairment of goodwill, provisions for income taxes, amounts receivable under the Collaboration Agreement, measurement of operating lease liabilities, and the fair value of stock options, stock appreciation rights, and restricted stock units (RSUs) granted to employees, directors and consultants.

The Company’s estimates could be affected by external conditions, including those unique to the Company and general economic conditions. It is reasonably possible that these external factors could have an effect on the Company’s estimates and could cause actual results to differ from those estimates and assumptions.

Significant Accounting Policies

There have been no material changes to the Company’s significant accounting policies from those described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, other than as set forth below.

Stock-Based Compensation

The Company expenses stock-based compensation to employees and Board members over the requisite service period based on the estimated grant-date fair value of the awards. Stock-based awards with graded-vesting schedules are recognized on a straight-line basis over the requisite service period for each separately vesting portion of the award.

Prior to the adoption of ASU 2018-07 on January 1, 2019, the Company remeasures the fair value of the non-employee awards at each reporting period prior to vesting and finally at the vesting date of the award. Changes in the estimated fair value of these non-employee awards are recognized as compensation expense in the period of change. Subsequent to the adoption of ASU 2018-07, the Company recognizes non-employees compensation costs over the requisite service period based on a measurement of fair value for each stock award.

The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model and the assumptions used in calculating the fair value of stock-based awards represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment.

The fair value of restricted stock units is determined based on the number of shares granted and the quoted market price of the Company's common stock on the date of grant. The fair value of restricted stock units with performance conditions deemed probable of being achieved and vesting are amortized to expense over the requisite service period using the straight-line method of expense recognition.

Leases

All of the Company’s leases are operating leases for facilities and equipment. Prior to January 1, 2019, the Company recognized related rent expense on a straight-line basis over the term of the lease. Incentives granted under the Company’s facilities lease, including allowances for leasehold improvements and rent holidays, were recognized as reductions to rental expense on a straight-line basis over the term of the lease. Deferred rent consisted of the difference between cash payments and the rent expense recognized.

Subsequent to the adoption of the new leasing standard on January 1, 2019, the Company recognizes a lease asset for its right to use the underlying asset and a lease liability for the corresponding lease obligation. The Company determines whether an arrangement is or contains a lease at contract inception. Operating leases are included in operating lease right-of-use assets, operating lease liabilities - short-term, and operating lease liabilities - long-term in our condensed consolidated balance sheet at March 31, 2019. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the net present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. The incremental borrowing rate represents the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably assured the Company will exercise the option to extend the contract. Periods covered by an option to extend are included in the lease term if the lessor controls the exercise of that option.

The operating lease right-of-use assets also include any lease payments made and exclude lease incentives. Lease expense is recognized on a straight-line basis over the expected lease term. Variable lease expenses are recorded when incurred. The Company has elected to not separate lease and non-lease components for its leased assets and account for all lease and non-lease components of its agreements as a single lease component.

Net Loss per Share

Basic net loss per common share excludes dilution and is computed by dividing net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per common share reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the entity unless inclusion of such shares would be anti-dilutive. Since the Company has only incurred losses, basic and diluted net loss per share is the same.

Securities that could potentially dilute loss per share in the future that were not included in the computation of diluted loss per share at March 31, 2019 and 2018 are as follows:

	Three Months Ended March 31,
	2019		2018
Warrants to purchase common stock		15,296		15,296
Options to purchase common stock		5,111,590		4,826,361
Unvested restricted stock units		607,656		251,559
Total		5,734,542		5,093,216

A reconciliation of the numerators and the denominators of the basic and diluted net (loss) income per common share computations is as follows (in thousands, except per share amounts):

	Three Months Ended March 31,
	2019			2018
Numerator:
Net (loss) income (in thousands)	$	(27,052	)	$	(16,249	)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share		25,668,798			20,231,804
Net (loss) income per share:
Basic	$	(1.05	)	$	(0.80	)
Diluted	$	(1.05	)	$	(0.80	)

Adoption of Recent Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02,

Leases

(ASU 2016-02). Under this standard, which applies to both lessors and lessees, lessees will be required to recognize all leases (except for short-term leases) as a lease liability, which is a lessee’s obligation to make lease payments arising from a lease measured on a discounted basis, and as a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. Leases will be classified as either financing or operating, with classification affecting the pattern of expense recognition in the income statement.

The Company adopted the ASU 2016-02 on January 1, 2019 using the modified retrospective approach and elected the package of practical expedients permitted under transition guidance, which allowed the Company to carry forward its historical assessments of: 1) whether contracts are or contain leases, 2) lease classification and 3) initial direct costs. The Company did not elect the practical expedient allowing the use-of-hindsight which would require the Company to reassess the lease term of its leases based on all facts and circumstances through the effective date and did not elect the practical expedient pertaining to land easements as this is not applicable to the current contract portfolio. The Company elected the post-transition practical expedient to not separate lease components from nonlease components for all existing lease classes. The Company also elected a policy of not recording leases on its condensed consolidated balance sheets when the leases have a term of 12 months or less and the Company is not reasonably certain to elect an option to purchase the leased asset.

The adoption of this standard resulted in the recognition of a ROU assets and lease liabilities of $13.8 million and $14.0 million, respectively, and the derecognition of the deferred rent balance of $0.1 million as of January 1, 2019. The adoption of the standard had no impact on the Company’s condensed consolidated statements of operations and comprehensive loss or to its cash flows from or used in operating, financing, or investing activities on its condensed consolidated statements of cash flows. No cumulative-effect adjustment within accumulated deficit was required to be recorded as a result of adopting this standard.

On January 1, 2019, the Company adopted ASU 2018-02,

Income Statement - Reporting Comprehensive Income, (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income,

which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the federal corporate income tax rate enacted under the Tax Cuts and Jobs Act (the Tax Act). The amount of the reclassification would be the difference between the historical corporate income tax rate and the Tax Act’s

21%

corporate income tax rate. The Company’s adoption of this standard did not have a material impact on its condensed consolidated financial statements.

On January 1, 2019, the Company adopted ASU 2018-15,

Intangibles (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract

, which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This new standard also requires customers to expense the capitalized implementation costs of a hosting arrangement that is a service contract over the term of the hosting arrangement. This new standard can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company is currently evaluating the effect that the updated standard will have on its condensed consolidated financial statements and related disclosures.

On January 1, 2019, the Company adopted ASU 2018-07,

Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting

(ASU 2018-17). ASU 2018-07 simplifies several aspects of the accounting for nonemployee share-based payment transactions resulting from expanding the scope of Topic 718,

Compensation – Stock Compensation

to include share-based payment transactions for acquiring goods and services from nonemployees. The Company’s adoption of this standard did not have a material impact on its condensed consolidated financial statements.

In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532,

Disclosure Update and Simplification

. The amendments became effective on November 5, 2018 and impacts the Company’s condensed consolidated financial statements through, among other things, the addition of a requirement to present a statement of stockholders’ equity for interim periods. As a result of adopting this guidance, the Company is presenting comparative interim statements of stockholders’ equity in this Form 10-Q for the quarter ended March 31, 2019 and 2018. Additionally, the guidance also simplified certain non-material disclosures in its SEC filings.

Recent Accounting Pronouncements

In November 2018, the FASB issued ASU 2018-18,

Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606

, 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. The standard is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted, including adoption in any interim period for public business entities for periods in which financial statements have not been issued. 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 Company is currently assessing the impact of this standard on its condensed consolidated financial statements.

In August 2018, the FASB issued ASU 2018-13,

Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement,

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. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted upon issuance of the update. The Company does not expect the adoption of this guidance to have a material impact on its condensed consolidated financial statements and related disclosures.

In June 2016, the FASB issued ASU 2016-13,

Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments

, 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. The new standard will be effective on January 1, 2020. Early adoption is available. The Company is currently evaluating the effect that the updated standard will have on its condensed consolidated financial statements and related disclosures.

Investments in Marketable Securities

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Investments in Marketable Securities

Note 3 – Investments in Marketable Securities

The carrying amounts of cash equivalents and marketable securities approximate their fair value based upon quoted market prices. Certain of the Company’s financial instruments are not measured at fair value on a recurring basis, but are recorded at amounts that approximate their fair value due to their liquid or short-term nature, such as cash, accounts receivable, accounts payable, accrued expenses, lease liability-short term and deferred revenue-short term.

The Company uses the following three-level hierarchy that maximizes the use of observable inputs and minimizes the use of unobservable inputs to value its financial instruments:

Level 1: Observable inputs such as unadjusted quoted prices in active markets for identical instruments.

Level 2: Quoted prices for similar instruments that are directly or indirectly observable in the marketplace.

Level 3: Significant unobservable inputs which 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 at:

	March 31, 2019
($ in thousands)	Amortized Cost		Gross Unrealized ‎ Gain (1)		Gross Unrealized ‎ Loss (1)			Fair Value
Short-term available-for-sale debt securities
U.S. and foreign corporate debt securities	$	60,799	$	12	$	(10	)	$	60,801
Asset-backed securities		33,002		17		(2	)		33,017
U.S. treasury securities		29,866		7		-			29,873
U.S. and foreign commercial paper		40,738		-		-			40,738
Total	$	164,405	$	36	$	(12	)	$	164,429

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

	December 31, 2018
($ in thousands)	Amortized Cost		Gross Unrealized ‎ Gain (1)		Gross Unrealized ‎ Loss (1)			Fair Value
Short-term available-for-sale debt securities
Corporate bonds	$	101,701	$	-	$	(122	)	$	101,579
Treasury securities		19,898		-		(4	)		19,894
Commercial paper		55,136		-		-			55,136
Total	$	176,735	$	-	$	(126	)	$	176,609

(1)

Gross unrealized gain (loss) is pre-tax.

The contractual term to maturity of short-term marketable securities held by the Company as of March 31, 2019 is less than one year. There were no long-term marketable securities held by the Company as of March 31, 2019.

Realized gains and losses for the three months ended March 31, 2018 and 2017 were not significant. The unrealized losses for the Company’s investments that have been in a continuous unrealized loss position for more than 12 months as of March 31, 2019 and December 31, 2018 were also not significant.

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

	March 31, 2019
($ in thousands)	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	25,434	$	-	$	-	$	25,434
Total cash equivalents		25,434		-		-		25,434

Short-term investments
U.S. and foreign corporate debt securities		-		60,801		-		60,801
Asset-backed securities		-		33,017		-		33,017
U.S. treasury securities		-		29,873		-		29,873
U.S. and foreign commercial paper		-		40,738		-		40,738
Total short-term investments		-		164,429		-		164,429
Total assets measured at fair value	$	25,434	$	164,429	$	-	$	189,863

	December 31, 2018
($ in thousands)	Level 1		Level 2		Level 3		Fair Value
Cash equivalents:
Money market funds	$	39,345	$	-	$	-	$	39,345
U.S. and foreign commercial paper		-		-		-
Total cash equivalents		39,345						39,345
Short-term investments:
U.S. and foreign commercial paper		-		55,136		-		55,136
U.S. and foreign corporate debt securities		-		73,159		-		73,159
Asset-backed securities		-		28,419		-		28,419
U.S. treasury securities		-		19,895		-		19,895
Total short-term investments		-		176,609		-		176,609
Total assets measured at fair value	$	39,345	$	176,609	$	-	$	215,954

The Company estimates the fair value of its corporate debt, asset-backed securities, and U.S. treasury securities 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, 2019

Property, Plant and Equipment [Abstract]

Property and Equipment, net

Note 4 -

Property and Equipment, net

Property and equipment consists of the following:

			March 31,			December 31,
($ in thousands)	Useful life (Years)		2019			2018
Computer hardware and software		3	$	-		$	194
Lab equipment		3 to 5		215			407
Office equipment		7		633			70
Leasehold improvement		1 to 3.25		722			790
Total property and equipment				1,570			1,461
Less: Accumulated depreciation and amortization				(838	)		(1,057	)
Construction in progress		N/A		1,347			153
Property and equipment, net			$	2,079		$	557

Depreciation expense for the three months ended March 31, 2019 and 2018 was approximately $0.1 million and $0.2 million, respectively, and was recorded in both research and development expense and general and administrative expense in the unaudited condensed consolidated statements of operations and comprehensive loss.

Accrued Expenses

3 Months Ended

Mar. 31, 2019

Payables and Accruals [Abstract]

Accrued Expenses

Note 5 – Accrued Expenses

Accrued expenses consist of the following:

	March 31,		December 31,
($ in thousands)	2019		2018
Accrued expenses:
Accrued compensation	$	2,276	$	5,011
Accrued clinical trial expenses		6,638		3,561
Accrued professional fees and other		1,227		1,107
Total accrued expenses	$	10,141	$	9,679

Stockholders' Equity

3 Months Ended

Mar. 31, 2019

Equity [Abstract]

Stockholders' Equity

Note 6 - Stockholders’ Equity

Common Stock

The Company was authorized to issue 5,000,000 shares of preferred stock as of March 31, 2019 and December 31, 2018. The Company was authorized to issue 100,000,000 shares of common stock as of March 31, 2019 and December 31, 2018.

For the three months ended March 31, 2019, the Company issued an aggregate of 21,000 shares of common stock and received gross proceeds of approximately $0.1 million from the exercise of options.

Stock-Based Compensation

3 Months Ended

Mar. 31, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Disclosure of Compensation Related Costs, Share-based Payments

Note 7 - Stock-Based Compensation

Equity Incentive Plans

In May 2018, the Company’s stockholders approved the Assembly Biosciences, Inc. 2018 Stock Incentive Plan (the 2018 Plan) pursuant to which the Company reserved 1,900,000 shares of its common stock for issuance in connection with equity incentive awards. In May 2018, the Company’s stockholders also approved the Assembly Biosciences, Inc. Employee Stock Purchase Plan (the 2018 ESPP), pursuant to which eligible employees can purchase an aggregate of up to 400,000

shares of the Company’s common stock at the end of predetermined offering periods at

85% of the lower of the fair market value at the beginning or end of the offering period.

As of March 31, 2019, the Company had awards outstanding under the following shareholder approved plans: 2010 Equity Incentive Plan (the 2010 Plan), which has been frozen; the Amended and Restated 2014 Stock Incentive Plan (the 2014 Plan); and the 2018 Plan. Shares of common stock underlying awards that are forfeited under the 2010 Plan on or after June 2, 2016 will become available for issuance under the 2014 Plan. Shares underlying awards that are forfeited under the 2014 Plan on or after May 30, 2018 will also become available for issuance under the 2018 Plan. As of March 31, 2019, the Company also had awards outstanding under the Assembly Biosciences, Inc. 2017 Inducement Award Plan (the 2017 Plan).

The Company issues new shares of common stock to settle options exercised and upon settlement of vested RSUs.

Stock Plan Activity

Stock Options

A summary of the Company’s option activity and related information for the three-month period ended March 31, 2019 is as follows:

	Number of Shares			Weighted Average Exercise Price Per Share		Total Intrinsic Value (in thousands)
Outstanding as of December 31, 2018		4,637,145		$	17.21	$	48,179
Granted		506,750			20.06		-
Exercised		(21,000	)		6.68		290
Forfeited		(11,305	)		27.28		48
Outstanding as of March 31, 2019		5,111,590		$	17.52	$	38,619
Options vested and exercisable		3,340,107		$	11.37	$	35,303

Restricted Stock Units (RSU)

A summary of the Company's RSUs and related information is as follows:

	Number of RSUs			Weighted average grant price
Outstanding as of December 31, 2018		568,005		$	37.18
Granted		215,928			19.69
Vested and settled		(63,920	)		46.03
Forfeited		(690	)		49.14
Outstanding as of March 31, 2019		719,323	(1)	$	31.13

(1)	Includes 111,667 RSUs that have vested but are subject to deferred settlement.

As of March 31, 2019, RSUs outstanding include 145,000 RSUs granted in December 2017 and 2018 with performance-based conditions to executives of the Company. Of these awards, 100,000 RSUs with a grant date fair value of $2.4 million vest over time but will be accelerated upon the achievement of certain performance conditions. The Company is recognizing expense for this award over the vesting period as it does not believe that any of the performance conditions are probable of being met. The remaining 45,000 RSUs with a grant date fair value of $1.9 million vest upon the performance conditions not yet deemed probable and accordingly no compensation expense has been recognized as of March 31, 2019 for these awards.

As of March 31, 2019, the Company had unrecognized stock-based compensation expense related to all unvested RSUs of $13.2 million. The weighted average remaining contractual term of unvested RSUs is approximately 9.6 years at March 31, 2019.

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,
	2019	2018
Exercise price	$ 19.69 - $23.04	$ 45.80 - $57.53
Expected volatility	75.0% - 83.2%	77.0% - 86.1%
Risk-free rate	2.24% - 2.65%	2.57% - 2.79%
Expected term (years)	5.5 – 7.0	5.5 - 7.0
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.

Stock-Based Compensation Expense

The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss:

	Three Months Ended March 31,
($ in thousands)	2019		2018
Research and development	$	2,728	$	2,524
General and administrative		3,849		1,559
Total stock-based compensation expense	$	6,577	$	4,083

Collaboration Agreement

3 Months Ended

Mar. 31, 2019

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 Allergan an exclusive worldwide license to certain of its intellectual property, including its intellectual property arising under the Collaboration Agreement, to develop and commercialize licensed compounds for UC, Crohn’s disease, and two compounds for IBS. Allergan and the Company also agreed to collaborate on research and development activities with respect to the licensed compounds in accordance with a mutually agreed upon research and development plan. Per the terms of the Collaboration Agreement, Allergan can select backups and additional target indications to add to the licenses granted for additional consideration and also has

the ability to enter into a contract manufacturing agreement with the Company for compound supply at cost plus an agreed upon margin. In addition, the Company will participate on a Joint Development Committee (JDC) and Joint Patent Committee (JPC). The Company provided to Allegan standard indemnification and protection of licensed intellectual property, which is part of assurance that the license meets the contract’s specifications and is not an obligation to provide goods or services.

Allergan paid the Company an upfront non-refundable payment of $50.0 million, which was received in 2017. Additionally,

the Company is eligible to receive variable consideration in the form of research and development cost reimbursements, up to approximately $631.0 million related to seven development milestones and up to approximately $2.14 billion related to 12 commercial development and sales milestones in connection with the successful development and commercialization of licensed compounds.

In addition, the Company is eligible to receive tiered royalties at rates ranging from the mid-single digits to the mid-teens based on net sales.

Allergan and the Company have agreed to share research and development costs up to an aggregate of $75.0 million through proof-of-concept (POC) studies on a ⅔, ⅓ basis, respectively, and Allergan has agreed to assume all post-POC development costs.

In the event any pre-POC development costs exceed $75.0 million in the aggregate, the Company may elect either (a) to fund ⅓ of such costs in excess of $75.0 million or (b) to allow Allergan to deduct from future development milestone payments ⅓ of the development costs funded by Allergan in excess of $75.0 million plus a premium of 25%. The Company has an option to co-promote the licensed programs in the U.S. and China, subject to certain conditions set forth in the Collaboration Agreement.

Allergan may terminate the Collaboration Agreement at any time upon either 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 are in development

, and

(ii) expiration of the last to exist valid claim covering the manufacture, use and sale of the licensed compounds. 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 Allegan is a customer and that the Collaboration Agreement

is not subject to accounting literature on collaborative arrangements. This is because the Company granted to Allergan licenses to its intellectual property, and research and development services, all of which are outputs of the Company’s ongoing activities, in exchange for consideration. The Company identified the following material promises under the

Collaboration Agreement

: (1) transfer of a 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, that it is only uniquely able to perform, in order for Allergan to benefit from the Licenses. As such, the Company determined that it has four performance obligations under the Collaboration Agreement associated with the transfer of the four compound Licenses combined with the performance of the Development Services for each of the four compound indications. The Company determined that the four performance obligations will be performed over the duration of the contract, which began in February 2017 and ends upon completion of the Development Services which is currently estimated to occur in 2024. 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 Allegan. 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 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 March 31, 2019. As part of the Company’s evaluation of the development and commercialization milestones constraint, the Company determined that the achievement of such milestones are 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, 2019 and 2018, the Company recorded approximately $3.9 million and $3.6 million, respectively, in revenue associated with the Collaboration Agreement. Short-term and long-term deferred revenue contract liabilities related to the Collaboration Agreement were approximately $9.9 million and approximately $29.9 million at March 31, 2019 and approximately $5.1 million and approximately $35.6 million at December 31, 2018.

On the unaudited condensed consolidated balance sheets, contract asset balances of approximately $3.0 million and approximately $2.4 million were recorded as accounts receivable from collaboration as of March 31, 2019 and December 31, 2018, respectively.

The following table presents changes in the Company’s contract liabilities ($ in thousands):

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

	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Three Months Ended March 31, 2018
Contract liabilities:
Deferred revenue	$	45,551	$	-	$	(1,231	)	$	44,320

		Three Months Ended
		March 31,
($ in thousands)		2019		2018
Collaboration revenue recognized in the period from:
Amounts included in deferred revenue at the beginning of the period	$	859	$	1,231
Performance obligations satisfied in previous period		-		-

Milestones and Research Agreements

3 Months Ended

Mar. 31, 2019

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 approximately $0.8 million, with a portion related to the first performance milestone having been paid. The Company also is obligated to pay IURTC royalty payments based on net sales of the licensed technology. The Company is also obligated to pay diligence maintenance fees each year to the extent that the royalty, sublicensing, and milestone payments to IURTC are less than the diligence maintenance fee for that year. Amounts paid in the three months ended March 31, 2019 and 2018 were insignificant.

Microbiome Targeted Colonic Delivery Platform

In November 2013, the Company entered into a License and Collaboration Agreement with Therabiome, LLC (Therabiome), for all intellectual property and know-how owned or controlled by Therabiome relating to the oral delivery of pharmaceutical drugs to specific sites in the intestine, using a pH sensitive controlled release capsule-in-capsule technology. The Company will be solely responsible for all research and development activities with respect to any product it develops under the license.

The Company must pay Therabiome clinical and regulatory milestones for each product or therapy advanced from the platform for U.S. regulatory milestones. The Company also must pay Therabiome lesser amounts for foreign regulatory milestones, which vary by country and region. The Company also must pay Therabiome royalties on annual net sales of a product in the low to mid-single digit percentages plus, once annual net sales exceed certain thresholds, a one-time cash payment upon reaching the thresholds.

Therabiome must pay the Company royalties on annual net sales of any product Therabiome is permitted to develop using the intellectual property in the low double to mid-double-digit percentages, depending on the level of development or involvement the Company had in the product.

A regulatory milestone was determined to have occurred and was

paid under this agreement as of and during the three months ended March 31, 2019.

No amounts

were accrued for this agreement as of and for the three months ended March 31, 2018.

Leases

3 Months Ended

Mar. 31, 2019

Lease, Cost [Abstract]

Lessee, Operating Lease, Disclosure [Table Text Block]

Note 10 - Leases

Operating Leases

The Company leases office space for corporate and administrative functions in Carmel, Indiana under a lease agreement that expires in August 2023. The Company leases office and laboratory space in South San Francisco, California under a sub-sublease that expires in December 2023. Prior to moving into the South San Francisco office and laboratory space in February 2019, the Company leased office and laboratory space in San Francisco, California, under a sublease that expired on February 28, 2019. The Company also leases office and laboratory space in Groton, Connecticut under a lease that expires in March 2020.

Our China subsidiary leases office space in Shanghai that expires in June 2019 and rents lab space in Shanghai that expires in December 2019. Additionally, our China subsidiary leases office space in Beijing that expires in December 2019. Certain lease contracts contain renewal clauses which the company assesses on a case by case basis. The Company also leases certain laboratory equipment accounted for as operating leases. These equipment leases began to expire in 2017, with the final lease expiring in 2021.

When the Company cannot determine the implicit rate in its leasing arrangements the Company uses its incremental borrowing rate as the discount rate when measuring operating lease liabilities. The incremental borrowing rate represents an estimate of the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease within a particular currency environment.

At March 31, 2019, the Company had operating lease liabilities of $13.2 million and right-of-use assets of $13.1 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, 2019
Lease cost
Operating lease cost	$	1,091
Short-term lease cost		321
Variable lease cost		299
Total lease cost	$	1,711

($ in thousands)	Three Months Ended March 31, 2019
Operating cash flows from operating leases	$	1,037
Right-of-use assets exchanged for new operating lease liabilities	$	-
Weighted-average remaining lease term – operating leases		4.5
Weighted-average discount rate – operating leases		9.6	%

As of March 31, 2019, the maturities of the Company’s operating lease liabilities were as follows (in thousands):

2019 (from April to December)	$	2,915
2020		3,735
2021		3,250
2022		3,267
2023		3,303
Total undiscounted future minimum lease payments		16,470
Less: present value adjustment		(3,245	)
Operating lease liabilities	$	13,225

Operating lease cost for three months

ended March 31, 2019 and 2018

were

approximately $1.1 million and $0.4 million, respectively.

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

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Basis of presentation

Basis of Presentation

Use of Estimates

Significant Accounting Policies

Stock-based Compensation

Stock-Based Compensation

Leases

Net Loss per Share

Securities that could potentially dilute loss per share in the future that were not included in the computation of diluted loss per share at March 31, 2019 and 2018 are as follows:

	Three Months Ended March 31,
	2019		2018
Warrants to purchase common stock		15,296		15,296
Options to purchase common stock		5,111,590		4,826,361
Unvested restricted stock units		607,656		251,559
Total		5,734,542		5,093,216

A reconciliation of the numerators and the denominators of the basic and diluted net (loss) income per common share computations is as follows (in thousands, except per share amounts):

	Three Months Ended March 31,
	2019			2018
Numerator:
Net (loss) income (in thousands)	$	(27,052	)	$	(16,249	)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share		25,668,798			20,231,804
Net (loss) income per share:
Basic	$	(1.05	)	$	(0.80	)
Diluted	$	(1.05	)	$	(0.80	)

Recent Accounting Pronouncements

Adoption of Recent Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02,

Leases

On January 1, 2019, the Company adopted ASU 2018-02,

Income Statement - Reporting Comprehensive Income, (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income,

21%

corporate income tax rate. The Company’s adoption of this standard did not have a material impact on its condensed consolidated financial statements.

On January 1, 2019, the Company adopted ASU 2018-15,

Intangibles (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract

On January 1, 2019, the Company adopted ASU 2018-07,

Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting

(ASU 2018-17). ASU 2018-07 simplifies several aspects of the accounting for nonemployee share-based payment transactions resulting from expanding the scope of Topic 718,

Compensation – Stock Compensation

In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532,

Disclosure Update and Simplification

Recent Accounting Pronouncements

In November 2018, the FASB issued ASU 2018-18,

Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606

In August 2018, the FASB issued ASU 2018-13,

Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement,

In June 2016, the FASB issued ASU 2016-13,

Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments

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

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

Securities that could potentially dilute loss per share in the future that were not included in the computation of diluted loss per share at March 31, 2019 and 2018 are as follows:

	Three Months Ended March 31,
	2019		2018
Warrants to purchase common stock		15,296		15,296
Options to purchase common stock		5,111,590		4,826,361
Unvested restricted stock units		607,656		251,559
Total		5,734,542		5,093,216

Schedule of Earnings Per Share, Basic and Diluted

A reconciliation of the numerators and the denominators of the basic and diluted net (loss) income per common share computations is as follows (in thousands, except per share amounts):

	Three Months Ended March 31,
	2019			2018
Numerator:
Net (loss) income (in thousands)	$	(27,052	)	$	(16,249	)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share		25,668,798			20,231,804
Net (loss) income per share:
Basic	$	(1.05	)	$	(0.80	)
Diluted	$	(1.05	)	$	(0.80	)

Investments in Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-sale Securities Reconciliation

Investments in marketable securities consisted of the following at:

	March 31, 2019
($ in thousands)	Amortized Cost		Gross Unrealized ‎ Gain (1)		Gross Unrealized ‎ Loss (1)			Fair Value
Short-term available-for-sale debt securities
U.S. and foreign corporate debt securities	$	60,799	$	12	$	(10	)	$	60,801
Asset-backed securities		33,002		17		(2	)		33,017
U.S. treasury securities		29,866		7		-			29,873
U.S. and foreign commercial paper		40,738		-		-			40,738
Total	$	164,405	$	36	$	(12	)	$	164,429

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

	December 31, 2018
($ in thousands)	Amortized Cost		Gross Unrealized ‎ Gain (1)		Gross Unrealized ‎ Loss (1)			Fair Value
Short-term available-for-sale debt securities
Corporate bonds	$	101,701	$	-	$	(122	)	$	101,579
Treasury securities		19,898		-		(4	)		19,894
Commercial paper		55,136		-		-			55,136
Total	$	176,735	$	-	$	(126	)	$	176,609

(1)

Gross unrealized gain (loss) is pre-tax.

Fair Value Measurements, Recurring and Nonrecurring [Table Text Block]

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

	March 31, 2019
($ in thousands)	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	25,434	$	-	$	-	$	25,434
Total cash equivalents		25,434		-		-		25,434

Short-term investments
U.S. and foreign corporate debt securities		-		60,801		-		60,801
Asset-backed securities		-		33,017		-		33,017
U.S. treasury securities		-		29,873		-		29,873
U.S. and foreign commercial paper		-		40,738		-		40,738
Total short-term investments		-		164,429		-		164,429
Total assets measured at fair value	$	25,434	$	164,429	$	-	$	189,863

	December 31, 2018
($ in thousands)	Level 1		Level 2		Level 3		Fair Value
Cash equivalents:
Money market funds	$	39,345	$	-	$	-	$	39,345
U.S. and foreign commercial paper		-		-		-
Total cash equivalents		39,345						39,345
Short-term investments:
U.S. and foreign commercial paper		-		55,136		-		55,136
U.S. and foreign corporate debt securities		-		73,159		-		73,159
Asset-backed securities		-		28,419		-		28,419
U.S. treasury securities		-		19,895		-		19,895
Total short-term investments		-		176,609		-		176,609
Total assets measured at fair value	$	39,345	$	176,609	$	-	$	215,954

- 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, 2019

Property, Plant and Equipment [Abstract]

Property and Equipment

Property and equipment consists of the following:

			March 31,			December 31,
($ in thousands)	Useful life (Years)		2019			2018
Computer hardware and software		3	$	-		$	194
Lab equipment		3 to 5		215			407
Office equipment		7		633			70
Leasehold improvement		1 to 3.25		722			790
Total property and equipment				1,570			1,461
Less: Accumulated depreciation and amortization				(838	)		(1,057	)
Construction in progress		N/A		1,347			153
Property and equipment, net			$	2,079		$	557

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2019

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following:

	March 31,		December 31,
($ in thousands)	2019		2018
Accrued expenses:
Accrued compensation	$	2,276	$	5,011
Accrued clinical trial expenses		6,638		3,561
Accrued professional fees and other		1,227		1,107
Total accrued expenses	$	10,141	$	9,679

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Schedule Of Share Based Compensation Stock Options Activity

A summary of the Company’s option activity and related information for the three-month period ended March 31, 2019 is as follows:

	Number of Shares			Weighted Average Exercise Price Per Share		Total Intrinsic Value (in thousands)
Outstanding as of December 31, 2018		4,637,145		$	17.21	$	48,179
Granted		506,750			20.06		-
Exercised		(21,000	)		6.68		290
Forfeited		(11,305	)		27.28		48
Outstanding as of March 31, 2019		5,111,590		$	17.52	$	38,619
Options vested and exercisable		3,340,107		$	11.37	$	35,303

Schedule of Restricted Stock Number of units

A summary of the Company's RSUs and related information is as follows:

	Number of RSUs			Weighted average grant price
Outstanding as of December 31, 2018		568,005		$	37.18
Granted		215,928			19.69
Vested and settled		(63,920	)		46.03
Forfeited		(690	)		49.14
Outstanding as of March 31, 2019		719,323	(1)	$	31.13

(1)	Includes 111,667 RSUs that have vested but are subject to deferred settlement.

Assumptions for Weighted Average Fair Value of Options Granted

The fair value of the stock options granted or modified during the periods indicated was estimated using the Black-Scholes option pricing model, based on the following assumptions:

	Three Months Ended March 31,
	2019	2018
Exercise price	$ 19.69 - $23.04	$ 45.80 - $57.53
Expected volatility	75.0% - 83.2%	77.0% - 86.1%
Risk-free rate	2.24% - 2.65%	2.57% - 2.79%
Expected term (years)	5.5 – 7.0	5.5 - 7.0
Dividend yield	0%	0%

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs

The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss:

	Three Months Ended March 31,
($ in thousands)	2019		2018
Research and development	$	2,728	$	2,524
General and administrative		3,849		1,559
Total stock-based compensation expense	$	6,577	$	4,083

Collaboration Agreement (Tables)

3 Months Ended

Mar. 31, 2019

Collaboration Agreement [Abstract]

Contract with Customer, Asset and Liability

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, 2019
Contract liabilities:
Deferred revenue	$	40,660	$	-	$	(859	)	$	39,801

	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Three Months Ended March 31, 2018
Contract liabilities:
Deferred revenue	$	45,551	$	-	$	(1,231	)	$	44,320

Schedule of Collaboration revenue recognized with the period

		Three Months Ended
		March 31,
($ in thousands)		2019		2018
Collaboration revenue recognized in the period from:
Amounts included in deferred revenue at the beginning of the period	$	859	$	1,231
Performance obligations satisfied in previous period		-		-

Leases (Tables)

3 Months Ended

Mar. 31, 2019

Lease, Cost [Abstract]

Disclosure of quantitative information of operating leases

The following summarizes quantitative information about the Company’s operating leases:

($ in thousands)	Three Months Ended March 31, 2019
Lease cost
Operating lease cost	$	1,091
Short-term lease cost		321
Variable lease cost		299
Total lease cost	$	1,711

($ in thousands)	Three Months Ended March 31, 2019
Operating cash flows from operating leases	$	1,037
Right-of-use assets exchanged for new operating lease liabilities	$	-
Weighted-average remaining lease term – operating leases		4.5
Weighted-average discount rate – operating leases		9.6	%

Lessee, Operating Lease, Liability, Maturity

As of March 31, 2019, the maturities of the Company’s operating lease liabilities were as follows (in thousands):

2019 (from April to December)	$	2,915
2020		3,735
2021		3,250
2022		3,267
2023		3,303
Total undiscounted future minimum lease payments		16,470
Less: present value adjustment		(3,245	)
Operating lease liabilities	$	13,225

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	5,734,542	5,093,216
Warrants To Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	15,296	15,296
Options To Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	5,111,590	4,826,361
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	607,656	251,559

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Details 1) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net (loss) income	$ (27,052)	$ (16,249)
Denominator:
Weighted average common shares outstanding for diluted net (loss) income per share	25,668,798	20,231,804
Net (loss) income per share:
Basic	$ (1.05)	$ (0.80)
Diluted	$ (1.05)	$ (0.80)

- 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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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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 - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2019	Jan. 01, 2019
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Operating Lease, Liability		$ 13,225	$ 14,000
Operating Lease, Right-of-Use Asset	$ 0	$ 13,063	$ 13,800
Lessee, Operating Lease, Term of Contract			12 months
Deferred Rent Credit			$ 100

Investments in Marketable Securities (Details) - USD ($)
$ in Thousands

Mar. 31, 2019

Dec. 31, 2018

Debt Securities, Available-for-sale [Line Items]

Amortized Cost

$ 164,405

$ 176,735

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

(12)

(126)

Fair Value

164,429

176,609

Short-term available-for-sale debt securities | US Government Agencies Debt Securities [Member]

Debt Securities, Available-for-sale [Line Items]

Amortized Cost

60,799

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

(10)

Fair Value

60,801

Short-term available-for-sale debt securities | Asset-backed Securities [Member]

Debt Securities, Available-for-sale [Line Items]

Amortized Cost

33,002

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

(2)

Fair Value

33,017

Short-term available-for-sale debt securities | US Treasury Securities [Member]

Debt Securities, Available-for-sale [Line Items]

Amortized Cost

29,866

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

Fair Value

29,873

Short-term available-for-sale debt securities | US foreign commercial paper member [Member]

Debt Securities, Available-for-sale [Line Items]

Amortized Cost

40,738

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

Fair Value

$ 40,738

Short-term available-for-sale debt securities | Corporate Bond Securities [Member]

Debt Securities, Available-for-sale [Line Items]

Amortized Cost

101,701

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

(122)

Fair Value

101,579

Short-term available-for-sale debt securities | US Treasury Securities [Member]

Debt Securities, Available-for-sale [Line Items]

Amortized Cost

19,898

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

(4)

Fair Value

19,894

Short-term available-for-sale debt securities | Commercial Paper [Member]

Debt Securities, Available-for-sale [Line Items]

Amortized Cost

55,136

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

Fair Value

$ 55,136

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

Investments in Marketable Securities (Details 1) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Cash Equivalents, at Carrying Value [Abstract]
Money market funds	$ 25,434
Fair Value, Measurements, Recurring [Member]
Cash Equivalents, at Carrying Value [Abstract]
Money market funds		$ 39,345
U.S. and foreign commercial paper	25,434	39,345
Total cash equivalents	25,434	39,345
Short-term Investments [Abstract]
U.S. and foreign commercial paper	164,429	176,609
Assets, Fair Value Disclosure	189,863	215,954
Short-term Investments	164,429	176,609
US Government Agencies Debt Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	60,801	73,159
Short-term Investments	60,801	73,159
Asset-backed Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	33,017	28,419
Short-term Investments	33,017	28,419
US Treasury Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	29,873	19,895
Short-term Investments	29,873	19,895
Commercial Paper [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	40,738	55,136
Short-term Investments	40,738	55,136
Fair Value, Inputs, Level 1 [Member]
Cash Equivalents, at Carrying Value [Abstract]
Money market funds		39,345
U.S. and foreign commercial paper		0
Total cash equivalents		0
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0
Short-term Investments	0
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Cash Equivalents, at Carrying Value [Abstract]
Money market funds	25,434
U.S. and foreign commercial paper	25,434	39,345
Total cash equivalents	25,434	39,345
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Assets, Fair Value Disclosure	25,434	39,345
Short-term Investments	0	0
Fair Value, Inputs, Level 1 [Member] \| US Government Agencies Debt Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper		0
Short-term Investments		0
Fair Value, Inputs, Level 1 [Member] \| Asset-backed Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Short-term Investments	0	0
Fair Value, Inputs, Level 1 [Member] \| US Treasury Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Short-term Investments	0	0
Fair Value, Inputs, Level 1 [Member] \| Commercial Paper [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Short-term Investments	0	0
Fair Value, Inputs, Level 2 [Member]
Cash Equivalents, at Carrying Value [Abstract]
Money market funds		0
U.S. and foreign commercial paper		0
Total cash equivalents		0
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Cash Equivalents, at Carrying Value [Abstract]
Money market funds	0
U.S. and foreign commercial paper	0
Total cash equivalents	0
Short-term Investments [Abstract]
U.S. and foreign commercial paper	164,429	176,609
Assets, Fair Value Disclosure	164,429	176,609
Short-term Investments	164,429	176,609
Fair Value, Inputs, Level 2 [Member] \| US Government Agencies Debt Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	60,801	73,159
Short-term Investments	60,801	73,159
Fair Value, Inputs, Level 2 [Member] \| Asset-backed Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	33,017	28,419
Short-term Investments	33,017	28,419
Fair Value, Inputs, Level 2 [Member] \| US Treasury Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	29,873	19,895
Short-term Investments	29,873	19,895
Fair Value, Inputs, Level 2 [Member] \| Commercial Paper [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	40,738	55,136
Short-term Investments	40,738	55,136
Fair Value, Inputs, Level 3 [Member]
Cash Equivalents, at Carrying Value [Abstract]
Money market funds		0
U.S. and foreign commercial paper		0
Total cash equivalents		0
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Cash Equivalents, at Carrying Value [Abstract]
Money market funds	0
U.S. and foreign commercial paper	0
Total cash equivalents	0
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Assets, Fair Value Disclosure	0	0
Short-term Investments	0	0
Fair Value, Inputs, Level 3 [Member] \| US Government Agencies Debt Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Short-term Investments	0	0
Fair Value, Inputs, Level 3 [Member] \| Asset-backed Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Short-term Investments	0	0
Fair Value, Inputs, Level 3 [Member] \| US Treasury Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Short-term Investments	0	0
Fair Value, Inputs, Level 3 [Member] \| Commercial Paper [Member] \| Fair Value, Measurements, Recurring [Member]
Short-term Investments [Abstract]
U.S. and foreign commercial paper	0	0
Short-term Investments	$ 0	$ 0

Property and Equipment, net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property, and equipment	$ 1,570	$ 1,461
Less: Accumulated depreciation and amortization	(838)	(1,057)
Property, and equipment, net	2,079	557
Computer hardware and software [Member]
Property, Plant and Equipment [Line Items]
Total property, and equipment	$ 0	194
Property, and Equipment, Useful Life	3 years
Lab equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, and equipment	$ 215	407
Lab equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, and Equipment, Useful Life	3 years
Lab equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, and Equipment, Useful Life	5 years
Office equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, and equipment	$ 633	70
Property, and Equipment, Useful Life	7 years
Leasehold improvement [Member]
Property, Plant and Equipment [Line Items]
Total property, and equipment	$ 722	790
Leasehold improvement [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, and Equipment, Useful Life	1 year
Leasehold improvement [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, and Equipment, Useful Life	3 years 3 months
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, and equipment	$ 1,347	$ 153

Property and Equipment, net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Property, Plant and Equipment [Line Items]
Depreciation	$ 0.1	$ 0.2

Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued expenses:
Accrued compensation	$ 2,276	$ 5,011
Accrued clinical trial expenses	6,638	3,561
Accrued professional fees and other	1,227	1,107
Total accrued expenses	$ 10,141	$ 9,679

Stockholders' Equity - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Stockholders Equity Note [Line Items]
Net proceeds raised from common stock issued in a public offering	$ 0.1
Common Stock, Shares, Issued	25,549,757	25,495,425
Common Stock, Shares Authorized	100,000,000	100,000,000
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Current Period [Member]
Stockholders Equity Note [Line Items]
Common Stock, Shares, Issued	21,000

Stock-Based Compensation (Details) - Stock Option [Member] $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Number of Shares
Options, Outstanding at beginning of period \| shares	4,637,145
Options, Granted \| shares	506,750
Options, Exercised \| shares	(21,000)
Options, Forfeited \| shares	(11,305)
Options, Outstanding at end of period \| shares	5,111,590
Options vested and exercisable \| shares	3,340,107
Weighted Average Exercise Price
Options, Outstanding at beginning of period \| $ / shares	$ 17.21
Options, Granted \| $ / shares	20.06
Options, Exercised \| $ / shares	6.68
Options, Forfeited \| $ / shares	27.28
Options, Outstanding at end of period \| $ / shares	17.52
Options vested and exercisable \| $ / shares	$ 11.37
Total Intrinsic Value
Options, Outstanding at beginning of period \| $	$ 48,179
Options, Granted \| $	0
Options, Exercised \| $	290
Options, Forfeited \| $	48
Options, Outstanding at end of period \| $	38,619
Options vested and exercisable \| $	$ 35,303

Stock-Based Compensation (Details 1) - Restricted Stock Units (RSUs) [Member]

3 Months Ended

Mar. 31, 2019

$ / shares

Beginning of period | shares

568,005

Number of units, Granted | shares

215,928

Number of units, Vested and settled | shares

(63,920)

Number of units, Forfeited | shares

(690)

Ending of period | shares

719,323

^[1]

Beginning of period | $ / shares

$ 37.18

Weighted average grant price, Granted | $ / shares

19.69

Weighted average grant price, Vested and settled | $ / shares

46.03

Weighted average grant price, Forfeited | $ / shares

49.14

Ending of period | $ / shares

$ 31.13

[1]	Includes 111,667 RSUs that have vested but are subject to deferred settlement.

Stock-Based Compensation (Details 2) - $ / shares	3 Months Ended		12 Months Ended
Stock-Based Compensation (Details 2) - $ / shares	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Dividend yield	0.00%		0.00%
Maximum [Member]
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Exercise price	$ 23.04	$ 57.53
Expected volatility	83.20%	86.10%
Risk-free rate	2.65%	2.79%
Expected term (years)	7 years	7 years
Minimum [Member]
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Exercise price	$ 19.69	$ 45.80
Expected volatility	75.00%	77.00%
Risk-free rate	2.24%	2.57%
Expected term (years)	5 years 6 months	5 years 6 months

Stock-Based Compensation (Details 3) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,577	$ 4,083
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	2,728	2,524
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 3,849	$ 1,559

Stock-Based Compensation - Additional Information (Details) - USD ($)
$ in Millions

3 Months Ended

May 31, 2018

Mar. 31, 2019

Dec. 31, 2018

Common Stock, Capital Shares Reserved for Future Issuance

1,900,000

Stock Issued During Period, Shares, New Issues

400,000

2018 Employee Stock Purchase Plan 2018 [Member]

Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent

85.00%

Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term

9 years 7 months 6 days

Share Based Compensation Arrangement By Share Based Payment Award Options Non vested In Period Fair Value1

$ 13.2

Restricted Stock Units (RSUs) [Member]

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number

719,323

^[1]

568,005

Restricted Stock Units (RSUs) [Member] | December 2017 [Member]

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number

145,000

Restricted Stock Units (RSUs) [Member] | December 2017 [Member] | Share-based Compensation Award, Tranche One [Member]

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number

100,000

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Weighted Average Grant Date Fair Amount

$ 2.4

Restricted Stock Units (RSUs) [Member] | December 2017 [Member] | Share-based Compensation Award, Tranche Two [Member]

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number

45,000

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Weighted Average Grant Date Fair Amount

$ 1.9

[1]	Includes 111,667 RSUs that have vested but are subject to deferred settlement.

Collaboration Agreement (Details) - Deferred revenue [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Change In Contract With Customer Liability [Line Items]
Balance at Beginning of Period	$ 40,660	$ 45,551
Additions	0	0
Deductions	(859)	(1,231)
Balance at End of Period	$ 39,801	$ 44,320

Collaboration Agreement (Details 1) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Collaboration revenue recognized in the period from:
Amounts included in deferred revenue at the beginning of the period	$ 859	$ 1,231
Performance obligations satisfied in previous period	$ 0	$ 0

Collaboration Agreement - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended
	Feb. 10, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 50,000
Accounts Receivable, Net, Current		$ 2,987		$ 2,430
Collaborative Arrangement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue Recognition Multiple Deliverable Arrangements Determinations Of Selling Price Amount		12,500
Contract with Customer, Liability, Current		9,900		5,100
Contract with Customer, Liability, Noncurrent		29,900		$ 35,600
Cost Of Reimbursable Expenses		3,900	$ 3,600
Allergan Pharmaceuticals International Limited [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Proceeds From Upfront Payment		$ 50,000
Description Of Agree To Share Development Cost	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.
Revenue Recognition Milestone Methods Description	the Company is eligible to receive variable consideration in the form of research and development cost reimbursements, up to approximately $631.0 million related to seven development milestones and up to approximately $2.14 billion related to 12 commercial development and sales milestones in connection with the successful development and commercialization of licensed compounds.
Agreed To Share Amount Development Cost	$ 75,000

Milestones and Research Agreements - Additional Information (Details) $ in Millions	Mar. 31, 2019 USD ($)
Indiana University Research and Technology Corporation [Member]
Potential Milestone Payments	$ 0.8

Leases (Details) - USD ($) $ in Thousands	3 Months Ended
Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018
Operating lease cost	$ 1,091	$ 400
Short-term lease cost	321
Variable lease cost	299
Total lease cost	$ 1,711

Leases (Details 1) $ in Thousands	3 Months Ended
Leases (Details 1) $ in Thousands	Mar. 31, 2019 USD ($)
Operating cash flows from operating leases	$ 1,037
Right-of-use assets exchanged for new operating lease liabilities	$ 0
Weighted-average remaining lease term – operating leases	4 years 6 months
Weighted-average discount rate – operating leases	9.60%

Leases (Details 2) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
2019 (from April to December)	$ 2,915
2020	3,735
2021	3,250
2022	3,267
2023	3,303
Total undiscounted future minimum lease payments	16,470
Less: present value discount	(3,245)
Operating lease liabilities	$ 13,225	$ 14,000

Leases - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018
Operating Lease, Liability	$ 13,225		$ 14,000
Operating Lease, Right-of-Use Asset	13,063		$ 13,800	$ 0
Operating Lease, Cost	$ 1,091	$ 400

Employee Benefit Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Retirement Benefits [Abstract]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0.2	$ 0.3