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Document And Entity Information - USD ($) $ in Millions	12 Months Ended
Document And Entity Information - USD ($) $ in Millions	Dec. 31, 2018	Feb. 25, 2019	Jun. 30, 2018
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Registrant Name	ASSEMBLY BIOSCIENCES, INC.
Entity Central Index Key	0001426800
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 745
Trading Symbol	ASMB
Entity Common Stock, Shares Outstanding		25,540,757
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	false

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 41,471	$ 82,033
Marketable securities, at fair value	176,609	37,914
Accounts receivable from collaboration	2,430	2,274
Prepaid expenses and other current assets	1,992	898
Total current assets	222,502	123,119
Long-term assets
Marketable securities, at fair value	0	3,347
Property, plant and equipment, net	557	860
Other assets	3,348	340
Indefinite-lived intangible asset	29,000	29,000
Goodwill	12,638	12,638
Total long-term assets	45,543	46,185
Total assets	268,045	169,304
Current liabilities
Accounts payable	3,693	2,124
Accrued expenses	9,679	6,139
Deferred revenue - short-term	5,100	5,229
Total current liabilities	18,472	13,492
Long-term liabilities
Deferred rent	108	0
Deferred tax liabilities	3,252	2,136
Deferred revenue - long-term	35,560	40,556
Total long-term liabilities	38,920	42,692
Total liabilities	57,392	56,184
Commitments and contingencies
Stockholders' equity
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.001 par value; 100,000,000 and 50,000,000 shares authorized as of December 31, 2018 and December 31, 2017; 25,495,425 and 20,137,974 shares issued and outstanding as of December 31, 2018 and December 31, 2017, respectively	25	20
Additional paid-in capital	552,762	364,528
Accumulated other comprehensive loss	(347)	(392)
Accumulated deficit	(341,787)	(251,036)
Total stockholders' equity	210,653	113,120
Total liabilities and stockholders' equity	$ 268,045	$ 169,304

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
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	50,000,000
Common stock, shares issued	25,495,425	20,137,974
Common stock, shares outstanding	25,495,425	20,137,974

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaboration revenue	$ 14,804	$ 9,019	$ 0
Operating expenses:
Research and development	72,741	44,225	33,093
General and administrative	34,798	17,021	12,185
Total operating expenses	107,539	61,246	45,278
Loss from operations	(92,735)	(52,227)	(45,278)
Other income (expenses)
Interest and other income	3,083	983	1,539
Loss on sale of marketable securities	0	(615)	(1,140)
Total other income	3,083	368	399
Loss before income taxes	(89,652)	(51,859)	(44,879)
Income tax (expenses) benefit	(1,099)	9,050	618
Net loss	(90,751)	(42,809)	(44,261)
Other comprehensive (loss) income
Unrealized gain (loss) on marketable securities, net of tax	45	209	221
Comprehensive loss	$ (90,706)	$ (42,600)	$ (44,040)
Net loss per share, basic and diluted	$ (3.98)	$ (2.41)	$ (2.57)
Weighted average common shares outstanding, basic and diluted	22,801,644	17,750,380	17,226,245

CONSOLIDATED STATEMENTS 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, 2015	$ 118,741	$ 17	$ 283,512	$ (822)	$ (163,966)
Balance (in shares) at Dec. 31, 2015		17,225,662
Proceeds from the exercise of stock options	153	$ 0	153	0	0
Proceeds from the exercise of stock options (in shares)		21,200
Change in unrealized loss on marketable securities, net of tax	221	$ 0	0	221	0
Cancellation of common stock	0	$ 0	0	0	0
Cancellation of common stock (in shares)		(108)
Stock-based compensation	5,024	$ 0	5,024	0	0
Net loss	(44,261)	0	0	0	(44,261)
Balance at Dec. 31, 2016	79,878	$ 17	288,689	(601)	(208,227)
Balance (in shares) at Dec. 31, 2016		17,246,754
Proceeds from common stock sold, net of underwriters' discounts and cost	64,848	$ 3	64,845	0	0
Proceeds from common stock sold, net of underwriters' discounts and cost (in shares)		2,541,500
Proceeds from the exercise of stock options	2,393	$ 0	2,393	0	0
Proceeds from the exercise of stock options (in shares)		349,720
Change in unrealized loss on marketable securities, net of tax	209	$ 0	0	209	0
Stock-based compensation	8,601	0	8,601	0	0
Net loss	(42,809)	0	0	0	(42,809)
Balance at Dec. 31, 2017	113,120	$ 20	364,528	(392)	(251,036)
Balance (in shares) at Dec. 31, 2017		20,137,974
Proceeds from common stock sold, net of underwriters' discounts and cost	155,425	$ 4	155,421	0	0
Proceeds from common stock sold, net of underwriters' discounts and cost (in shares)		4,600,000
Proceeds from the exercise of stock options	3,960	$ 1	3,959	0	0
Proceeds from the exercise of stock options (in shares)		735,030
Issuance of common stock under Employee Stock Purchase Plan (ESPP)	408	$ 0	408	0	0
Issuance of common stock under Employee Stock Purchase Plan (ESPP) (in shares)		21,483
Settlement of restricted stock units into common stock	0	$ 0	0	0	0
Settlement of restricted stock units into common stock (in shares)		938
Change in unrealized loss on marketable securities, net of tax	45	$ 0	0	45	0
Stock-based compensation	28,446	0	28,446	0	0
Net loss	(90,751)	0	0	0	(90,751)
Balance at Dec. 31, 2018	$ 210,653	$ 25	$ 552,762	$ (347)	$ (341,787)
Balance (in shares) at Dec. 31, 2018		25,495,425

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net loss	$ (90,751)	$ (42,809)	$ (44,261)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	643	219	80
Stock-based compensation	28,485	8,601	5,024
Amortization of discount on marketable securities, net	(229)	0	0
Realized loss from marketable securities	0	615	1,140
Deferred income tax expenses (benefit)	1,099	(9,050)	(618)
Changes in operating assets and liabilities:
Accounts receivable from collaboration	(156)	(2,273)	0
Prepaid expenses and other current assets	(1,094)	(286)	93
Other assets	(3,008)	(84)	(58)
Accounts payable	1,569	(244)	1,004
Accrued expenses	3,501	1,386	2,714
Deferred revenue	(5,125)	45,785	0
Deferred rent	108	0	0
Net cash (used in) provided by operating activities	(64,958)	1,860	(34,882)
Cash flows from investing activities
Purchases of fixed assets	(340)	(865)	(147)
Purchases of marketable securities	(183,941)	(48,234)	(7,951)
Redemptions of marketable securities	48,884	33,457	44,294
Net cash (used in) provided by investing activities	(135,397)	(15,642)	36,196
Cash flows from financing activities
Proceeds from common stock sold, net of underwriters' discounts and cost	155,425	64,847	0
Proceeds from issuance of common stock under ESPP	408	0	0
Proceeds from the exercise of stock options	3,960	2,393	153
Net cash provided by financing activities	159,793	67,240	153
Net (decrease) increase in cash and cash equivalents	(40,562)	53,458	1,467
Cash and cash equivalents at the beginning of the period	82,033	28,575	27,108
Cash and cash equivalents at the end of the period	$ 41,471	$ 82,033	$ 28,575

Nature of Business

12 Months Ended

Dec. 31, 2018

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 platform programs: a new class of oral therapeutic candidates for the treatment of hepatitis B virus (HBV) infection and a novel class of oral synthetic live biotherapeutic candidates, which are designed to treat disorders 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 additional product candidates for other disease indications, including Crohn’s disease, irritable bowel syndrome, 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 consolidated 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 7 for recent sales of common stock). 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 studies.

Summary of Significant Accounting Policies and Recent Accounting Pronouncements

12 Months Ended

Dec. 31, 2018

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

These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (U.S. GAAP) and include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with the accounting principles generally accepted in the United States of America (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 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, 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.

Cash and cash equivalents

All highly liquid investments with maturities of three months or less at the time of purchase are considered to be cash equivalents. All of the

Company’s

cash equivalents have liquid markets and high credit ratings. The Company maintains its cash in bank deposits and other accounts, the balances of which, at times and at December 31, 2018 and 2017, exceed federally insured limits.

Investments in Marketable Securities

The Company has designated marketable securities as of December 31, 2018 and 2017 as available-for-sale securities and measures these securities at their respective fair values. Marketable securities are classified as short-term or long-term based on the maturity date and their availability to meet current operating requirements. Marketable securities that mature in one year or less are classified as short-term available-for-sale securities and are reported as a component of current assets.

Securities that are classified as available-for-sale are measured at fair value with temporary unrealized gains and losses reported in other comprehensive loss, and as a component of stockholders' equity until their disposition. The Company reviews all available-for-sale securities at each period end to determine if they remain available-for-sale based on their current intent and ability to sell the security if it is required to do so. Declines in value judged to be other-than- temporary are included in interest income or expense in the Company’s statements of operations and comprehensive loss. Realized gains and losses from the sale of marketable securities, if any, are calculated using the specific-identification method.

Marketable securities are subject to a periodic impairment review. The Company may recognize an impairment charge when a decline in the fair value of investments below the cost basis is determined to be other-than-temporary. In determining whether a decline in market value is other-than-temporary, various factors are considered, including the cause, duration of time and severity of the impairment, any adverse changes in the

investees’

financial condition, and the

Company’s

intent and ability to hold the security for a period of time sufficient to allow for an anticipated recovery in market value. There were no marketable securities deemed to be impaired as of December 31, 2018 or 2017.

Goodwill and Indefinite-Lived Other Intangible Assets

Goodwill and indefinite-lived intangible assets are reviewed for impairment at least annually in the fourth quarter, and more frequently if events or other changes in circumstances indicate that the carrying amount of the assets may not be recoverable. Impairment of goodwill and indefinite-lived intangibles is determined to exist when the fair value is less than the carrying value of the net assets being tested.

Goodwill

The difference between the purchase price and the fair value of assets acquired and liabilities assumed in a business combination is allocated to goodwill. Goodwill is evaluated for impairment on an annual basis as of October 1, and more frequently if indicators are present or changes in circumstances suggest that impairment may exist.

As of October 1, 2018, the Company has determined through its quantitative impairment test that the fair value of its goodwill significantly exceeded the carrying value of its single reporting unit, and concluded that goodwill was not impaired. The Company has not recognized any goodwill impairment in any of the periods presented.

Indefinite-Lived Intangible Asset

The

Company’s

indefinite-lived intangible asset consists of IPR&D acquired in a business combination that are used in research and development activities but have not yet reached technological feasibility, regardless of whether they have alternative future use. The primary basis for determining the technological feasibility or completion of these projects is obtaining regulatory approval to market the underlying products in an applicable geographic region. The Company classifies IPR&D acquired in a business combination as an indefinite-lived intangible asset until the completion or abandonment of the associated research and development efforts. Upon completion of the associated research and development efforts, the Company performed a final test for impairment and will determine the useful life of the technology and begin amortizing the assets to reflect their use over their remaining lives. Upon permanent abandonment, the Company would write-off the remaining carrying amount of the associated IPR&D intangible asset.

In performing each annual impairment assessment and any interim impairment assessment, the Company determines if it should qualitatively assess whether it is more likely than not that the fair value of its IPR&D asset is less than its carrying amount (the qualitative impairment test). If the Company concludes that is the case, or elect not to use qualitative impairment test, the Company would proceed with quantitatively determining the fair value of the IPR&D asset and comparing its fair value to its carrying value to determine the amount of impairment, if any (the quantitative impairment test).

When performing the quantitative impairment assessment, the Company uses the income approach to determine the fair value of its IPR&D asset. This approach calculates fair value by estimating the after-tax cash flows attributable to an in-process project over its useful life and then discounting these after-tax cash flows back to a present value. This estimate includes significant assumptions regarding the estimates that market participants would make in evaluating the IPR&D asset, including the probability of successfully completing clinical trials and obtaining regulatory approval to market the IPR&D asset, the timing of and the expected costs to complete IPR&D projects, future net cash flows from potential drug sales, which are based on estimates of the sales price of the drug, the size of the patient population and cure rate, our competitive position in the marketplace, and appropriate discount and tax rates. Any impairment to be recorded is calculated as the difference between the fair value of the IPR&D asset as of the date of the assessment with the carrying value of the IPR&D asset on its consolidated balance sheet.

In performing the qualitative impairment test, the Company considers the results of the most recent quantitative impairment test and identifies the most relevant drivers of the fair value for the IPR&D asset. The most relevant drivers of fair value identified are consistent with the assumptions used in the quantitative estimate of the IPR&D asset discussed below. Using these drivers of fair value, the Company identifies events and circumstances that may have an effect on the fair value of the IPR&D asset since the last time the

IPR&D’s

fair value was quantitatively determined. The Company then weighs these factors to determine and conclude if it is not more likely than not that the IPR&D asset is impaired. If it is more likely than not that the IPR&D asset is impaired, the Company proceeds with quantitatively determining the fair value of the IPR&D asset.

For 2018, the Company elected to bypass the quantitative assessment and performed a qualitative impairment on October 1 and concluded that it is more likely than not that the fair value of its IPR&D asset exceeded its carrying value and no further testing was required. The Company did not recognize any IPR&D impairment in any of the periods presented.

Leases

The Company leases office space facilities under non-cancelable operating lease agreements and recognizes related rent expense on a straight-line basis over the term of the lease. Landlord allowances and incentives received, including allowances for leasehold improvements and rent holidays, are recognized as reductions to rent expense on a straight-line basis over the term of the lease. The Company does not assume renewals in its determination of the lease term unless they are deemed to be reasonably assured at the inception of the lease. The Company begins recognizing rent expense on the date it obtains the legal right to use and control the leased space. Deferred rent consists of the difference between cash payments and the rent expense recognized.

Impairment of Long-lived Assets

The Company monitors the carrying value of long-lived assets for potential impairment and tests the recoverability of such assets whenever events or changes in circumstances indicate that the carrying amounts may not be recoverable. If a change in circumstance occurs, the Company performs a test of recoverability by comparing the carrying value of the asset or asset group to its undiscounted expected future cash flows. If cash flows cannot be separately and independently identified for a single asset, the Company will determine whether impairment has occurred for the group of assets for which the Company can identify the projected cash flows. If the carrying values are in excess of undiscounted expected future cash flows, the Company measures any impairment by comparing the fair value of the asset or asset group to its carrying value. There were no indicators of impairment of long-lived assets during the years ended December 31, 2018 and 2017.

Property and Equipment, Net

Property and equipment are stated at cost and consist of lab equipment and computer hardware and software. The Company computes depreciation under the straight-line method over the estimated useful lives of its property and equipment ranging from three to seven years.

Leasehold improvements are amortized over the remaining terms of the respective leases or the estimated useful life of the leasehold improvements, whichever is less. Maintenance and repair costs are expensed as incurred.

Fair Value Measurements

The Company follows accounting guidance on fair value measurements for financial instruments measured on a recurring basis, as well as for certain assets and liabilities that are initially recorded at their estimated fair values. Fair value is defined as the exit price, or the amount that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. 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.

Financial instruments measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The assessment of the significance of a particular input to the fair value measurement in its entirety requires us to make judgments and consider factors specific to the asset or liability. The use of different assumptions and/or estimation methodologies may have a material effect on estimated fair values. Accordingly, the fair value estimates disclosed or initial amounts recorded may not be indicative of the amount that the Company or holders of the instruments could realize in a current market exchange.

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 and accrued expenses.

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

	As of December 31, 2018
	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

	As of December 31, 2017
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents:
Money market funds	$	1,663	$	-	$	-	$	1,663
U.S. commercial paper
Total cash equivalents		1,663		-		-		1,663
Short-term investments:
U.S. and foreign corporate debt securities		-		37,914		-		37,914
Total short-term investments		-		37,914		-		37,914
Long-term investments:
U.S. and foreign corporate debt securities		-		3,347		-		3,347
Total long-term investments		-		3,347		-		3,347
Total assets measured at fair value		1,663		41,261		-		42,924

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.

Revenue Recognition and Accounts Receivable

At the inception of an arrangement, we evaluate if a counterparty to a contract is a customer, if the arrangement is within the scope of revenue from contracts with customers guidance, and the term of the contract. We recognize revenue when the customer obtains control of promised goods or services in a contract for an amount that reflects the consideration we expect to receive in exchange for those goods or services. For contracts with customers, we apply the following five-step model in order to determine this amount: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) we satisfy each performance obligation. Our performance obligations under these arrangements may include licenses of intellectual property, options to license additional intellectual property, research and development services, delivery of manufactured product, and/or participation on joint steering committees. Allergan can select additional and/or back-up target indications to add to the licenses granted and also has the ability to enter into a contract manufacturing agreement with us for compound supply, and we have concluded that these rights are options. We evaluated whether such options contained material rights and concluded they 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.

We have provided standard indemnification and protection of licensed intellectual property for our customer. These provisions are part of assurance that the licenses meet the agreements, representations and are not obligations to provide goods or services.

We only apply the five-step model to contracts when it is probable that we will collect the consideration we are entitled to in exchange for the goods or services we transfer to the customer. As part of the accounting for contracts with customers, we must develop assumptions that require judgment to determine the standalone selling price of each performance obligation identified in the contract. We then allocate the total transaction price to each performance obligation based on the estimated standalone selling prices of each performance obligation. For the Allergan agreement, we estimated standalone selling prices of our performance obligations using income-based valuation approach for the estimated value a licensor of the compounds would receive. We recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when the performance obligation is satisfied or as it is satisfied. For our contract with Allergan, we recognize revenues for each of our distinct performance obligations as the related research and development services are performed because Allergan consumes the benefit of research and development work simultaneously as we perform these services.

Upfront License Fees:

If a license to our intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, we recognize revenues from nonrefundable, upfront license fees based on the relative value prescribed to the license compared to the total value of the arrangement. The revenue is recognized when the license is transferred to the collaborator and the collaborator is able to use and benefit from the license. For licenses that are not distinct from other obligations identified in the arrangement, we utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time. If the combined performance obligation is satisfied over time, we apply an appropriate method of measuring progress for purposes of recognizing revenue from nonrefundable, upfront license fees. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition.

Development and Regulatory Milestone Payments

: Depending on facts and circumstances, we may record revenues from certain milestones in a reporting period before the milestone is achieved if we conclude that achievement of the milestone is probable and that recognition of revenue related to the milestone will not result in a significant reversal in amounts recognized in future periods. We record a corresponding contract asset when this conclusion is reached. Milestone payments that have not been included in the transaction price to date are fully constrained. We re-evaluate the probability of achievement of such milestones and any related constraint each reporting period. We adjust our estimate of the overall transaction price, including the amount of collaborative revenue that was recorded, if necessary.

Research and Development Service Payments

: We are reimbursed at a certain percentage for performing research and development services based on hours worked by our employees, at a fixed contractual rate per hour, and third-party pass-through costs we incur on a quarterly basis. Research and development service payments are included in the transaction price in the reporting period that we conclude that it is probable that recording revenue in the period will not result in a significant reversal in amounts recognized in future periods. Accounts receivable are recorded when the right to the research and development service payment consideration becomes unconditional. We record the full reimbursed portion of these expenses as collaboration revenue in our consolidated statements of operations as we consider performing research and development services to be a part of our ongoing and central operations.

Sales-based Milestone and Royalty Payments:

Our customers may be required to pay us sales-based milestone payments or royalties on future sales of commercial products. We recognize revenues related to sales-based milestone and royalty payments upon the later to occur of (i) achievement of the collaborator’s underlying sales or (ii) satisfaction of any performance obligation(s) related to these sales, in each case assuming our licensed intellectual property is deemed to be the predominant item to which the sales-based milestones and/or royalties relate.

We receive payments from our customers based on billing schedules established in each contract. Upfront payments and fees are recorded as deferred revenue upon receipt or when due until we perform our obligations under these arrangements. If the related performance obligation is expected to be satisfied within the next twelve months, these amounts will be classified in current liabilities. We recognize a contract asset relating to our conditional right to consideration that is not subject to a constraint. Amounts are recorded as accounts receivable when our right to consideration is unconditional. At December 31, 2018 and 2017, the accounts receivable recorded on the consolidated balance sheet relates to the Collaboration Agreement. All accounts receivables are deemed collectible. A net contract asset or liability is presented for each contract with a customer. We do not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.

Stock-Based Compensation

The Company measures stock-based compensation to employees, consultants, and Board members at fair value on the grant date of the award. The fair value of restricted stock units (RSUs) 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. Compensation cost is recognized as expense on a straight-line basis over the requisite service period of the award. Stock-based awards with graded vesting schedules are recognized on a straight-line basis over the requisite service period for each separately vesting tranche of the award. For awards that have a performance condition, compensation cost is measured based on the fair value on the grant date (the date performance targets are established) and is expensed over the requisite service period for each separately vesting tranche when achievement of the performance objective becomes probable. We assess the probability of the performance conditions being met on a continuous basis. Forfeitures are recognized when incurred.

The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model and the assumptions used in estimating the fair value of stock-based awards, such as expected term, dividends, volatility and risk-free interest rate, represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment. The Company is also required to make estimates as to the probability of achieving the specific performance conditions. If actual results are not consistent with the Company’s assumptions and judgments used in making these estimates, the Company may be required to increase or decrease compensation expense, which could be material to the Company’s consolidated results of operations.

We account for stock-based compensation arrangements with non-employees, which primarily consist of consultants, using a fair value approach. The fair value of these options is measured using the Black-Scholes Model reflecting the same assumptions as applied to employee options in each of the reported periods, other than the expected life, which is assumed to be the remaining contractual life of the option. The compensation costs of these arrangements are subject to remeasurement over the vesting terms as earned.

Research and Development Expense and Accruals

Research and development costs are expensed as incurred unless there is an alternative future use in other research and development projects. Research and development costs include salaries and personnel-related costs, consulting fees, fees paid for contract research services, fees paid to clinical research organizations, contract manufacturing organizations, license fees prior to FDA approval and other third parties associated with clinical studies, the costs of laboratory equipment and facilities, and other external costs. Payments made prior to the receipt of goods or services to be used in research and development are capitalized until the goods or services are received. Such payments are evaluated for current or long-term classification based on when they will be realized.

The Company records expenses related to clinical studies and manufacturing development activities based on its estimates of the services received and efforts expended pursuant to contracts with multiple contract research organizations (CROs) and manufacturing vendors that conduct and manage these activities on its behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract, and may result in uneven payment flows. There may be instances in which payments made to the Company’s vendors will exceed the level of services provided and result in a prepayment of the expense. Payments under some of these contracts depend on factors such as the successful enrollment of subjects and the completion of clinical study milestones. In amortizing or accruing service fees, the Company estimates the time period over which services will be performed, enrollment of subjects, number of sites activated and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the Company’s estimate, the Company will adjust the accrued or prepaid expense balance accordingly. To date, there have been no material differences from the Company’s estimates to the amounts actually incurred.

Costs related to our collaboration agreement are included in the research and development expense.

For asset purchases outside of business combinations, the Company expenses any purchased research and development assets as of the acquisition date if they have no alternative future uses.

Tax Assets and Liabilities and Income Taxes

The Company records income taxes using the asset and liability method. Deferred income tax assets and liabilities are recognized for the future tax effects attributable to temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective income tax bases, and operating loss and tax credit carryforwards. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company establishes a valuation allowance if it is more likely than not that the deferred tax assets will not be realized based on an evaluation of objective verifiable evidence. For tax positions that are more likely than not of being sustained upon audit, the Company recognizes the largest amount of the benefit that is greater than 50% likely of being realized. For tax positions that are not more likely than not of being sustained upon audit, the Company does not recognize any portion of the benefit.

The Company recognizes and measures uncertain tax positions using a two

step approach set forth in authoritative guidance. The first step is to evaluate the tax position taken or expected to be taken by determining whether the weight of available evidence indicates that it is more likely than not that the tax position will be sustained in an audit, including resolution of any related appeals or litigation processes. The second step is to measure the tax benefit as the largest amount that is more than 50% likely to be realized upon ultimate settlement. Significant judgment is required to evaluate uncertain tax positions. The Company evaluates uncertain tax positions on a regular basis. The evaluations are based on a number of factors, including changes in facts and circumstances, changes in tax law, correspondence with tax authorities during the course of the audit, and effective settlement of audit issues. The provision for income taxes includes the effects of any accruals that the Company believes are appropriate. It is the Company’s policy to recognize interest and penalties related to income tax matters in income tax expense. Through December 31, 2018, the Company had not accrued interest or penalties related to uncertain tax positions.

On December 22, 2017, the Securities and Exchange Commission staff issued Staff Accounting Bulletin No. 118 (SAB 118) to address the accounting implications of U.S. federal tax reform enacted on December 22, 2017. SAB 118 allows a company to record provisional amounts during a measurement period not to extend beyond one year from the enactment date (see Note 10).

Net Loss per Share of Common Stock

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 as follows:

	Year Ended December 31,
	2018		2017		2016
Warrants to purchase common stock		15,296		15,296		16,909
Options to purchase common stock		4,637,145		4,551,819		4,457,251
ESPP		21,483		-		-
RSUs		568,005		120,000		-
Total		5,241,929		4,687,115		4,474,160

Comprehensive Loss

Comprehensive loss is comprised of net loss and adjustments for the change in unrealized gains and losses on investments in available-for-sale marketable securities. The Company displays comprehensive loss and its components in the consolidated statements of operations and comprehensive loss, net of tax effects if any.

Concentrations of Credit Risk

Financial instruments which potentially subject the Company to credit risk consist primarily of cash, cash equivalents and marketable securities. The Company holds these investments in highly rated financial institutions, and, by policy, limits the amounts of credit exposure to any one financial institution. These amounts at times may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.

Adoption of Recent Accounting Pronouncements

On January 1, 2018, the Company adopted ASU No. 2014-09,

Revenue from Contracts with Customers

, as amended (Accounting Standards Codification Topic 606) (ASC 606) using the modified retrospective method applied to those contracts which were not completed as of January 1, 2018. The Company also elected to use the practical expedient that allows an entity to expense the incremental cost of obtaining a contract as an expense when incurred if the amortization period of the asset that an entity otherwise would have recognized is less than one year. Results for the year ended December 31, 2018 are presented under ASC 606, while prior period amounts are not adjusted and continue to be reported in accordance with historic accounting under previous revenue recognition guidance. As of the adoption date of ASC 606, we had only one contract with a customer, Allergan, that had not been completed. Based on our analysis, we concluded there was no significant change in applying ASC 606 to the Collaboration Agreement and no amounts have been recognized within “accumulated deficit” in the consolidated balance sheet related to the adoption of the new standard.

In January 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-01,

Recognition and Measurement of Financial Assets and Financial Liabilities (ASU 2016-01)

. ASU 2016-01 requires equity investments to be measured at fair value with changes in fair value recognized in net income; simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment; eliminates the requirement for public business entities to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet; requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes; requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments; requires separate presentation of financial assets and financial liabilities by measurement category and form of financial assets on the balance sheet or the accompanying notes to the financial statements and clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity’s other deferred tax assets. ASU 2016-01 is effective for financial statements issued for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years. On January 1, 2018, the Company implemented ASU 2016-01 without any impact on the Company’s consolidated financial statements and related disclosures.

In August 2016, the FASB issued ASU 2016-15,

Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments,

which addresses eight specific cash flow issues with the objective of reducing the existing diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. On January 1, 2018, the Company implemented ASU 2016-15 without any material impact on the Company’s consolidated statement of cash flows and related disclosures.

In May 2017, the FASB issued ASU 2017-09,

Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting (ASU 2017-09)

ASU 2017-09 provides clarity and reduces both (1) diversity in practice and (2) cost and complexity when applying the guidance in Topic 718, to a change to the terms or conditions of a share-based payment award. The amendments in ASU 2017-09 should be applied prospectively to an award modified on or after the adoption date. On January 1, 2018, the Company implemented ASU 2017-09 without any material impact on the Company’s consolidated financial statements and related disclosures.

In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532,

Disclosure Update and Simplification

, amending certain disclosure requirements that were redundant, duplicative, overlapping, outdated or superseded. In addition, the amendments expanded the disclosure requirements on the analysis of stockholders' equity for interim financial statements. Under the amendments, an analysis of changes in each caption of stockholders' equity presented in the balance sheet must be provided in a note or separate statement. The analysis should present a reconciliation of the beginning balance to the ending balance of each period for which a statement of comprehensive income is required to be filed. This final rule became effective on November 5, 2018. The Company implemented the final rule under SEC Release No. 33-10532 as of December 31, 2018. The Company had evaluated the impact of the amendments and determined the effect of the adoption of the simplification rules on financial statements will be limited to the modification and removal of certain disclosures.

Accounting Pronouncements to Be Adopted

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

Leases (Topic 842)

, which supersedes FASB Topic 840,

Leases (Topic 840)

and provides principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases. In January 2018, the FASB issued ASU 2018-01,

Leases (Topic 842) Land Easement Practical Expedient for Transition to Topic 842

, which amends ASU 2016-02 to provide entities an optional transition practical expedient to not evaluate under Topic 842 existing or expired land easements that were not previously accounted for as leases under the current leases guidance in Topic 842. An entity that elects this practical expedient should evaluate new or modified land easements under Topic 842 beginning at the date that the entity adopts Topic 842. In July 2018, the FASB also issued ASU 2018-11,

Leases (Topic 842): Targeted Improvements

, which provides an optional transition method that allows entities to elect to apply the standard prospectively at its effective date, versus recasting the prior periods presented. The standard will be effective for annual and interim periods beginning after December 15, 2018, with early adoption permitted upon issuance. The Company plans to implement Topic 842, using the optional transition method to apply the new guidance as of January 1, 2019, rather than as of the earliest period presented, and elected the package of practical expedients described above. The Company is still finalizing its analysis, but expects to recognize additional operating liabilities

with corresponding right of use (ROU) assets of approximately the same amount as of January 1, 2019 based on the present value of the remaining lease payments.

In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808):

Clarifying the Interaction between Topic 808 and Topic 606

(ASU 2018-18), 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 consolidated financial statements.

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. The new standard will be effective on January 1, 2020. Early adoption will be available on January 1, 2019. The Company is currently evaluating the effect that the updated standard will have on its consolidated financial statements and related disclosures.

In February 2018, the FASB issued ASU 2018-02,

Income Statement - Reporting Comprehensive Income, (Topic 220):

Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income

(ASU 2018-12)

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 new standard is effective for fiscal years and interim periods beginning after December 15, 2018 with early adoption permitted in any interim period. The Company plans to adopt the new standard effective January 1, 2019. The adoption of ASU 2018-02 will not have a material impact on its consolidated financial statements and related disclosures.

In August 2018, the FASB issued ASU No. 2018-15,

Intangibles

(Topic 350):

Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract

(ASU 2018-15), 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. ASU 2018-15 is effective for public companies for fiscal years beginning after December 15, 2019. This new standard can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company plans to adopt this standard effective January 1, 2019 and does not expect it will have a material impact on the Company is currently evaluating the impact of adoption on its consolidated financial statements.

In June 2018, the FASB issued ASU 2018-07,

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

(ASU 2018-07). ASU 2018-07 simplifies several aspects of the accounting for nonemployee share-based payment transactions resulting from expanding the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. ASU 2018-07 is effective for public business entities for fiscal years and interim periods beginning after December 15, 2018. The Company plans to adopt the new standard effective January 1, 2019. Upon adoption of ASU 2018-07, the grant date fair value of non-employee awards will be fixed as of December 31, 2018, rather than the prior methodology that recognizes a variable cost based on the fair value of such shares as of their vesting dates. The Company will record non-employees’ awards as of January 1, 2019 prospectively. The Company does not expect this ASU will have a material impact on its 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 consolidated financial statements and related disclosures.

ASU 2017-04,

Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment

simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. Under the amendments in ASU 2017-04, an entity should recognize an impairment charge for the amount by which the carrying amount of a reporting unit exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The updated guidance requires a prospective adoption. ASU 2017-04 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. The Company is currently evaluating the timing and impact of adopting this new accounting standard on its consolidated financial statements and related disclosures.

Investments in Marketable Securities

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Investments in Marketable Securities

Note 3 – Investments in Marketable Securities

Investments in marketable available-for-sale securities consisted of the following:

	December 31, 2018
($ in thousands)	Amortized Cost			Gross Unrealized Gain (1)	Gross Unrealized ‎ Loss (1)			Fair Value
Short-term available-for-sale 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

	December 31, 2017
			Gross Unrealized		Gross Unrealized
($ in thousands)	Amortized Cost		Gain (1)		Loss (1)			Fair Value
Short-term available-for-sale securities
Corporate bonds	$	38,092	$	6	$	(184	)	$	37,914
Long-term available-for-sale securities
Corporate bonds	$	3,357			$	(10	)	$	3,347
Total	$	41,449	$	6	$	(194	)	$	41,261

(1)

Gross unrealized gain (loss) is pre-tax.

The contractual term to maturity of short-term marketable securities held by the Company as of December 31, 2018 is less than one year. There were no long-term marketable securities held by the Company as of December 31, 2018.

Realized gains and losses for the years ended December 31, 2018, 2017 and 2016 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 December 31, 2018 and 2017 was also not significant.

Property, Plant and Equipment, Net

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment, Net

Note 4 – Property, Plant and Equipment, Net

Property, plant and equipment, consists of the following:

	As of December 31,
($ in thousands)	2018			2017
Computer hardware and software	$	194		$	105
Lab equipment		407			370
Office equipment		70			25
Construction in progress		153			-
Leasehold improvement		790			774
Total property, plant and equipment		1,614			1,274
Less: Accumulated depreciation and amortization		(1,057	)		(414	)
Property, plant and equipment, net	$	557		$	860

Depreciation expense for the years ended December 31, 2018, 2017 and 2016 was approximately $0.6 million, $0.2 million and $0.1 million, respectively, and was recorded in both research and development expense and general and administrative expense in the consolidated statements of operations and comprehensive loss.

Accrued Expenses

12 Months Ended

Dec. 31, 2018

Payables and Accruals [Abstract]

Accrued Expenses

Note 5 – Accrued Expenses

Accrued expenses consist of the following:

	As of December 31,
($ in thousands)	2018		2017
Accrued expenses:
Accrued compensation	$	5,011	$	4,518
Accrued clinical trial expenses		3,561		442
Accrued professional fees and other		1,107		1,179
Total accrued expenses	$	9,679	$	6,139

Stockholders' Equity

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Stockholders' Equity

Note 6 – Stockholders’ Equity

The Company is authorized to issue 5,000,000 shares of preferred stock as of December 31, 2018 and 2017, respectively. The Company was authorized to issue 50,000,000 shares of common stock as of December 31, 2017. In May 2018, the Company’s stockholders approved the adoption of the Fourth Amended and Restated Certificate of Incorporation, which amended and restated the Company’s Third Amended and Restated Certificate of Incorporation, as amended, to, among other things, increase the authorized number of shares of common stock, par value $0.001 per share, from 50,000,000 shares to 100,000,000 shares.

In January 2018, the Board of Directors authorized the filing of a Certificate of Elimination with the Secretary of State of the State of Delaware to remove the Certificate of Designation of Series A Non-Voting Convertible Preferred Stock (the Series A Preferred Stock) from the Company’s Third Amended and Restated Certificate of Incorporation, as amended (which was amended and restated in May 2018), because no shares of the Series A Preferred Stock were outstanding and no shares were available to be issued.

Sale of Common Stock

On November 6, 2017, the Company sold to various investors an aggregate of 2,541,000 shares of common stock in a public offering at $27.25 per share, which included the exercise in full by the underwriters of their option to purchase 331,500

additional

shares of common stock, which occurred on November 2, 2017.

The Company received aggregate net proceeds of $64.8 million from the offering and option exercise, after deducting underwriting discounts and commissions and offering expenses.

On December 29, 2017, the Company filed a registration statement on Form S-3 with the SEC using a “shelf” registration statement, file number 333-222366, which became effective January 10, 2018. 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). To date, the Company has not sold any shares pursuant to the ATM.

On July 16, 2018, the Company sold to various investors an aggregate of 4,600,000 shares of common stock in a public offering at $36.00 per share, which included the exercise in full by the underwriters of their option to purchase 600,000 additional shares of common stock, which occurred on July 12, 2018.

The Company received aggregate net proceeds of approximately $155.4 million from the offering and the option exercise, after deducting underwriting discounts and commissions and offering expenses payable by the Company.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2018

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

On May 30, 2018, the Company’s stockholders approved the Assembly Biosciences, Inc. 2018 Stock Incentive Plan (the 2018 Plan) pursuant to which the Company reserved 1,900,000

shares of its common stock for issuance in connection with equity incentive awards and the Assembly Biosciences, Inc. Employee Stock Purchase Plan (the 2018 ESPP).

As of December 31, 2018, 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 Stock Incentive Plan (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 December 31, 2018, the

Company also had awards outstanding under the Assembly Biosciences, Inc. 2017 Inducement Award Plan.

The Company issues new shares of common stock to settle options exercised or vested restricted stock units.

Stock Plan Activity

Stock Options

The following table summarizes the stock option activity and related information:

	Number of Shares			Weighted Average Exercise Price		Total Intrinsic Value (in thousands)
Outstanding as of December 31, 2016		4,457,251		$	7.14	$	23,258
Granted		706,800		$	24.16	$	15,792
Exercised		(353,612	)	$	7.03		-
Forfeited		(258,620	)	$	9.51		-
Outstanding as of December 31, 2017		4,551,819		$	9.66	$	162,002
Granted		998,603			44.19		-
Exercised		(775,224	)		7.34		31,134
Forfeited		(138,053	)		18.71		3,195
Outstanding as of December 31, 2018		4,637,145		$	17.21	$	48,179
Options vested and exercisable		3,077,195		$	9.21	$	42,503

The Company expects that all outstanding unvested options will vest. The weighted average remaining contractual term of exercisable options and awards outstanding is approximately

6.2

and 7.1 years, respectively, at December 31, 2018. As of December 31, 2018 estimated future stock-based compensation expense relating to unvested stock options was

$19.4 million.

RSUs

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

	Number of units			Weighted average grant price
Unvested as of December 31, 2016		-		$	-
Granted		120,000			44.28
Unvested as of December 31, 2017		120,000		$	44.28
Granted		456,559			35.54
Vested and Settled		(938	)		49.14
Forfeited		(7,616	)		49.14
Unvested as of December 31, 2018		568,005	(1)	$	37.18

(1) Includes 128,332 RSUs that have vested but are subject to deferred settlement.

As of December 31, 2018, 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 December 31, 2018 for these awards.

As of December 31, 2018, the Company had unrecognized stock-based compensation expense related to all unvested RSUs of $10.4 million, which is expected to be recognized over the remaining weighted-average contractual term is 9.2 years.

Common Stock Warrants

There was no warrant activity during the year ended December 31, 2018. During the year ended December 31, 2017, 1,613 warrants to purchase common stock expired unexercised. At December 31, 2018 and 2017 there were 15,296 warrants outstanding with a weighted average exercise price of $30.00 per share. The weighted average remaining contractual life of outstanding warrants at December 31, 2018 is approximately 1.7 years.

Employee Stock Purchase Plan

The 2018 ESPP provides for the purchase by employees of up to an aggregate

400,000

shares of the Company’s common stock at a discount to the market price. Subject to the annual statutory limits and the 2018 ESPP’s limit of 1,000 shares of common stock per offering, an eligible employee may participate through payroll deductions of up to 15% of such employee’s compensation for each pay period.

Eligible employees can purchase the Company’s common stock at the end of a predetermined offering period at 85% of the lower of the fair market value at the beginning or end of the offering period.

Under the 2018 ESPP, the offering periods end on the last business day occurring on or before May 14 or November 14.

The ESPP is compensatory and results in stock-based compensation expense.

In November

2018, employees purchased

21,483 shares

of common stock under the 2018 ESPP. As of December 31,2018,

378,517 shares of common stock

are available for future sale under the Company’s 2018 ESPP.

Stock-based compensation expense recorded in connection with the 2018 ESPP was approximately

$0.2 million for the year December 31, 2018.

Valuation Assumptions

The Company used the Black-Scholes option-pricing model for determining the estimated fair value and stock-based compensation for stock-based awards to employees and the board of directors. The assumptions used in the Black-Scholes option-pricing model were as follows:

	Year Ended December 31,
	2018	2017	2016
Exercise price	$23.78 - $57.53	$12.81 - $44.28	$5.84 - $13.21
Expected volatility	75.6% - 86.1%	81.2% - 87.0%	85.8% - 91.8%
Risk-free rate of interest	2.56% - 3.04%	2.02% - 2.29%	1.36% - 2.18%
Expected term (years)	5.5 - 7.0	5.5 - 7.0	5.3 - 7.0
Expected dividend yield	-	-	-

The risk-free interest rate assumption was based on the rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the stock option or purchase right being valued. The assumed dividend yield was zero as the Company currently does not intend to pay dividends in the foreseeable future. The weighted average expected term of options was calculated using the simplified method as prescribed by accounting guidance for stock-based compensation due to the Company’s limited history of relevant stock option exercise activity. The expected volatility was calculated based on the Company’s historical stock prices, supplemented as necessary with historical volatility of the common stock of several peer companies with characteristics similar to those of the Company.

Stock-Based Compensation Expense

The Company recognized stock-based compensation expense in continuing operations as follows:

	Year Ended December 31,
($ in thousands)	2018		2017		2016
Research and development	$	11,820	$	5,423	$	3,025
General and administrative		16,665		3,178		1,999
Total	$	28,485	$	8,601	$	5,024

Collaboration Agreement

12 Months Ended

Dec. 31, 2018

Collaboration Agreement [Abstract]

Collaboration Agreement

Note 8 - Collaboration Agreement

Allergan

In January 2017, the Company entered into and a Research, Development, Collaboration and License Agreement (the Collaboration Agreement) with Allergan Pharmaceuticals International Limited (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 ulcerative colitis (UC), Crohn’s disease, and two compounds for irritable bowel syndrome (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 have 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 (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 license and know how all revert to the Company.

The Company concluded that Allegan 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 license agreement: 1) transfer of a licenses to intellectual property for the four initial indications, inclusive of the related technology know-how (Licenses); 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 2027. 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 we conclude 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 December 31, 2018. 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 year ended December 31, 2018 and 2017, the Company recorded approximately $14.8 million and $9.0 million, respectively, in revenue associated with the Collaboration Agreement, respectively. Short-term and long-term deferred revenue contract liabilities related to the Collaboration Agreement were approximately $5.1 million and approximately $35.6 million at December 31, 2018 and approximately $5.2 million and approximately $40.6 million at December 31, 2017. Under the legacy revenue guidance in ASC 605,

Revenue Recognition

, the Company’s collaboration revenue for the year ended December 31, 2018, would not have differed materially.

On the consolidated balance sheets, contract asset balances of approximately

$2.4 million and approximately $2.3 million were recorded as accounts receivable from collaboration as of December 31, 2018 and 2017, 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
Year ended December 31, 2018
Contract liabilities:
Deferred revenue	$	45,785	$	—	$	(5,125	)	$	40,660

	Year Ended
	December 31,
($ in thousands)	2018
Collaboration revenue recognized in the period from:
Amounts included in deferred revenue at the beginning of the period	$	5,125
Performance obligations satisfied in previous period		—

Milestones and Research Agreements

12 Months Ended

Dec. 31, 2018

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. The Company made approximately

$0.1 million, in milestone

payments for the years ended December 31, 2018

. Amounts paid in 2017 or 2016 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. No amounts were incurred or accrued for this agreement as of and for the years ended December 31, 2018, 2017 and 2016.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

Note 10 - Income Taxes

There was no current income tax provision for the years ended December 31, 2018, 2017 and 2016. The Company recognized deferred income tax expense

of $1.1 million and a deferred income tax benefit of $9.1 million and $0.6

million for the years ended December 31, 2018, 2017 and 2016, respectively.

The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows:

	As of December 31,
	2018			2017			2016
Statutory federal income tax rate		(21.0	)%		(34.0	)%		(34.0	)%
State taxes, net of federal tax benefit		(7.1	)		(2.6	)		(4.3	)
Stock based compensation		(6.7	)		-			3.4
Credits		(2.4	)		(2.1	)		(1.8	)
Effective change in enacted tax rates		-			47.7			-
State rate change		(2.5	)		0.2			7.5
Other		(0.4	)		0.3			2.3
Change in valuation allowance		41.3			(27.0	)		25.5
Income taxes provision (benefit)		1.2	%		(17.5	)%		(1.4	)%

Significant components of the Company’s deferred tax assets and (liabilities) are as follows:

	As of December 31,
($ in thousands)	2018			2017
Deferred tax assets:
Federal and state-operating loss carryforwards	$	58,668		$	43,577
Stock-based compensation		14,023			5,726
Intangible assets		2,282			2,259
Deferred revenue		11,409			11,064
Research and development credits		5,472			5,604
Other		575			360
Total deferred tax assets		92,429			68,590
Valuation allowance		(87,543	)		(63,718	)
Deferred tax asset, net of allowance	$	4,886		$	4,872
In-process research and development		(8,138	)		(7,008	)
Net deferred tax liability	$	(3,252	)	$	(2,136	)

The Company maintains a valuation allowance on deferred tax assets due to the uncertainty regarding the ability to utilize these deferred tax assets in the future. The deferred tax liability was recorded in connection with the merger with Assembly Pharmaceuticals in

2014

and relates to the difference between the carrying amount of in-process

research and development

for financial statement purposes relative to the amount used for income tax purposes.

On December 22, 2017

, the Tax Act, was signed into law. Among other items, the Tax Act reduces the federal corporate tax rate to 21% from the existing applicable rate of 34%, effective January 1, 2018. As a result, in 2017 the Company recorded

a provisional estimate as

a decrease to its deferred tax assets of $24.7 million and to valuation allowance of $28.4 million, resulting in a net tax benefit of $3.7 million.

The Tax Act also permits an indefinite carry forward of net operating losses generated in taxable years ending after December 31, 2017, subject to a utilization limitation of 80% of taxable income. Due to the change in the carryforward period for post-2017 net operating losses, the Company determined that it would be able to use the deferred tax liability associated with certain in-process

research and development

as a source of income in determining the realizability of its deferred tax assets. As a result, in 2017 the Company recorded a $4.9 million income tax benefit from the reduction of its valuation allowance.

On December 22, 2017, Staff Accounting Bulletin No. 118, or SAB 118, was issued to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. The Company was able to provide a reasonable estimate for the revaluation of deferred taxes. The Company completed its review in December 2018

with no material adjustments to the provisional amount previously recorded.

The Company’s income tax benefit for the year ended December 31, 2017 of $9.1 million includes a tax benefit of $8.6 million related to the Tax Act.

As of December 31, 2018, the Company had potentially utilizable gross federal net operating loss carryforwards of approximately

$209.2

million with

$94.7

million of net operating losses generated during 2018 carrying forward indefinitely and $114.5 million of net operating losses beginning to expire between 2027 and 2038. There are state net operating loss carryforwards of $209.0 million beginning to expire between 2027 and 2038. In addition, the Company has federal research and development credit carryforwards of approximately $3.6 million which will expire between 2027 and 2038 and California research and development credit carryforwards of $1.9 million will carryforward indefinitely.

Pursuant to Internal Revenue Code (IRC), Section 382 and 383, use of the Company’s U.S. federal and state net operating loss and research and development income tax credit carryforwards may be limited in the event of a cumulative change in ownership of more than 50.0% within a three-year period. The Company has performed an ownership change study through December 31, 2017 and has determined that a “change in ownership” as defined by IRC Section 382 and the rules and

regulations

promulgated thereunder, did occur in December 2010, January 2013 and October 2014. The Company has adjusted its net operating loss carryovers to appropriately reflect any attributes which will expire due to the limitation. The Company has not performed any additional analysis for IRC Sections 382 and 383 and there is a risk that additional changes in ownership could have occurred since December 31, 2017. If a change in ownership were to have occurred, additional net operating loss and tax credit carryforwards could be eliminated or restricted. If eliminated, the related asset would be removed from the deferred tax asset schedule with a corresponding reduction in the valuation allowance.

The following table summarizes activity related to the Company’s gross unrecognized tax benefits (in thousands):

	Total
Balances as of December 31, 2016	$	-
Increases related to prior year tax positions		-
Increases related to 2017 tax positions		-
Balances as of December 31, 2017	$	-
Increases related to prior year tax positions		3,679
Increases related to 2018 tax positions		934
Balances as of December 31, 2018	$	4,613

The unrecognized tax benefits, if recognized, would not have an impact on the Company’s effective tax rate assuming the Company continues to maintain a full valuation allowance position. Based on prior year’s operations and experience, the Company does not expect a significant change to its unrecognized tax benefits over the next twelve months. The unrecognized tax benefits may increase or change during the next year for unexpected or unusual items for items that arise in the ordinary course of business. At December 31, 2018, the Company has not accrued for interest or penalties associated with unrecognized tax liabilities. In subsequent periods, any interest and penalties related to uncertain tax positions will be recognized as a component of income tax expense.

The Company files income tax returns in the U.S. federal and other state jurisdictions and is not currently under examination by federal, state, or local taxing authorities for any open tax years. Due to net operating loss

carryforwards, all years effectively remain open for income tax examination by tax authorities in the U.S. and states in which the Company files tax returns.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 11 - Commitments and Contingencies

Operating Leases

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

The Company ceased leasing laboratory space from Indiana University at Bloomington, Indiana in May 2017.

The Company ceased leasing office and laboratory space from the University of Florida Research Foundation in Alachua, Florida in May 2017.

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.

Future minimum lease payments under noncancelable operating leases are as follows:

2019	$	5,032
2020		4,537
2021		4,055
2022		4,075
2023		4,095
Total	$	21,794

Rent expense for the years ended December 31, 2018, 2017 and 2016 were approximately

$4.2

million, $2.1 million and $1.9 million, respectively.

Employee Benefit Plan

12 Months Ended

Dec. 31, 2018

Retirement Benefits [Abstract]

Employee Benefit Plan

Note 12 – Employee Benefit Plan

Effective

January 1, 2018,

the Company established a defined contribution 401(k) plan (the Plan) for all employees who are at least 21 years of age. Employees are eligible to participate in the Plan upon commencement of employment. Under the terms of the Plan, employees may make voluntary contributions as a percentage of compensation. The Plan also permits the Company to make discretionary matching contributions. In 2018, the Company made discretionary matching contributions of $0.7 million.

In 2017 and 2016, the Company participated in a professional employer organization sponsored 401(k) plan. The Company did not make any discretionary matching contributions in 2017 or 2016.

Selected Quarterly Financial Data

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data

Note 13 - Selected Quarterly Financial Data (Unaudited)

The following table contains quarterly financial information for fiscal years 2018 and 2017.

The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented.

($ in thousands except for per share amounts)	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
2018
Collaboration revenue	$	3,565		$	3,218		$	4,286		$	3,735
Operating expenses	$	20,237		$	30,384		$	26,861		$	30,057
Interest and other income	$	446		$	453		$	1,116		$	1,069
Unrealized loss from marketable securities, net of tax	$	(23	)	$	(127	)	$	(82	)	$	231
Net loss	$	(16,249	)	$	(26,806	)	$	(21,535	)	$	(26,161	)
Basic and diluted net loss per common share	$	(0.80	)	$	(1.30	)	$	(0.87	)	$	(1.03	)

2017
Collaboration revenue	$	684		$	2,359		$	2,660		$	3,315
Operating expenses	$	14,614		$	15,927		$	15,110		$	15,595
Interest and other income	$	136		$	240		$	241		$	366
Unrealized loss from marketable securities, net of tax	$	(137	)	$	(341	)	$	(99	)	$	(38	)
Net loss	$	(13,931	)	$	(13,599	)	$	(12,272	)	$	(3,007	)
Basic and diluted net loss per common share	$	(0.81	)	$	(0.78	)	$	(0.71	)	$	(0.16	)

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

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Basis of presentation

Basis of Presentation

Use of Estimates

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.

Cash and cash equivalents

All highly liquid investments with maturities of three months or less at the time of purchase are considered to be cash equivalents. All of the

Company’s

Investments in Marketable Securities

investees’

financial condition, and the

Company’s

Goodwill and Other Intangible Assets

Goodwill and Indefinite-Lived Other Intangible Assets

Goodwill

Indefinite-Lived Intangible Asset

The

Company’s

IPR&D’s

Leases

Impairment of Long-lived Assets

Property and Equipment

Property and Equipment, Net

Fair Value Measurements

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.

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

	As of December 31, 2018
	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

	As of December 31, 2017
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents:
Money market funds	$	1,663	$	-	$	-	$	1,663
U.S. commercial paper
Total cash equivalents		1,663		-		-		1,663
Short-term investments:
U.S. and foreign corporate debt securities		-		37,914		-		37,914
Total short-term investments		-		37,914		-		37,914
Long-term investments:
U.S. and foreign corporate debt securities		-		3,347		-		3,347
Total long-term investments		-		3,347		-		3,347
Total assets measured at fair value		1,663		41,261		-		42,924

There were no transfers between Level 1, Level 2 or Level 3 during the periods presented.

Revenue Recognition

Revenue Recognition and Accounts Receivable

Upfront License Fees:

Development and Regulatory Milestone Payments

Research and Development Service Payments

Sales-based Milestone and Royalty Payments:

Stock-based Compensation

Stock-Based Compensation

Research and Development Expense and Accruals

Costs related to our collaboration agreement are included in the research and development expense.

For asset purchases outside of business combinations, the Company expenses any purchased research and development assets as of the acquisition date if they have no alternative future uses.

Tax Assets and Liabilities and Income Taxes

The Company recognizes and measures uncertain tax positions using a two

Net Loss per Share of Common Stock

Securities that could potentially dilute loss per share in the future that were not included in the computation of diluted loss per share as follows:

	Year Ended December 31,
	2018		2017		2016
Warrants to purchase common stock		15,296		15,296		16,909
Options to purchase common stock		4,637,145		4,551,819		4,457,251
ESPP		21,483		-		-
RSUs		568,005		120,000		-
Total		5,241,929		4,687,115		4,474,160

Comprehensive Loss

Concentrations of Credit Risk

Recent Accounting Pronouncements

Adoption of Recent Accounting Pronouncements

On January 1, 2018, the Company adopted ASU No. 2014-09,

Revenue from Contracts with Customers

In January 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-01,

Recognition and Measurement of Financial Assets and Financial Liabilities (ASU 2016-01)

In August 2016, the FASB issued ASU 2016-15,

Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments,

In May 2017, the FASB issued ASU 2017-09,

Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting (ASU 2017-09)

In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532,

Disclosure Update and Simplification

Accounting Pronouncements to Be Adopted

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

Leases (Topic 842)

, which supersedes FASB Topic 840,

Leases (Topic 840)

Leases (Topic 842) Land Easement Practical Expedient for Transition to Topic 842

Leases (Topic 842): Targeted Improvements

with corresponding right of use (ROU) assets of approximately the same amount as of January 1, 2019 based on the present value of the remaining lease payments.

In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808):

Clarifying the Interaction between Topic 808 and Topic 606

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

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

(ASU 2016-13),

In February 2018, the FASB issued ASU 2018-02,

Income Statement - Reporting Comprehensive Income, (Topic 220):

Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income

(ASU 2018-12)

In August 2018, the FASB issued ASU No. 2018-15,

Intangibles

(Topic 350):

Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract

In June 2018, the FASB issued ASU 2018-07,

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

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,

ASU 2017-04,

Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment

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

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

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

	As of December 31, 2018
	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

	As of December 31, 2017
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents:
Money market funds	$	1,663	$	-	$	-	$	1,663
U.S. commercial paper
Total cash equivalents		1,663		-		-		1,663
Short-term investments:
U.S. and foreign corporate debt securities		-		37,914		-		37,914
Total short-term investments		-		37,914		-		37,914
Long-term investments:
U.S. and foreign corporate debt securities		-		3,347		-		3,347
Total long-term investments		-		3,347		-		3,347
Total assets measured at fair value		1,663		41,261		-		42,924

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 as follows:

	Year Ended December 31,
	2018		2017		2016
Warrants to purchase common stock		15,296		15,296		16,909
Options to purchase common stock		4,637,145		4,551,819		4,457,251
ESPP		21,483		-		-
RSUs		568,005		120,000		-
Total		5,241,929		4,687,115		4,474,160

Investments in Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-sale Securities Reconciliation

Investments in marketable available-for-sale securities consisted of the following:

	December 31, 2018
($ in thousands)	Amortized Cost			Gross Unrealized Gain (1)	Gross Unrealized ‎ Loss (1)			Fair Value
Short-term available-for-sale 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

	December 31, 2017
			Gross Unrealized		Gross Unrealized
($ in thousands)	Amortized Cost		Gain (1)		Loss (1)			Fair Value
Short-term available-for-sale securities
Corporate bonds	$	38,092	$	6	$	(184	)	$	37,914
Long-term available-for-sale securities
Corporate bonds	$	3,357			$	(10	)	$	3,347
Total	$	41,449	$	6	$	(194	)	$	41,261

(1)

Gross unrealized gain (loss) is pre-tax.

Property, Plant and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, plant and equipment, consists of the following:

	As of December 31,
($ in thousands)	2018			2017
Computer hardware and software	$	194		$	105
Lab equipment		407			370
Office equipment		70			25
Construction in progress		153			-
Leasehold improvement		790			774
Total property, plant and equipment		1,614			1,274
Less: Accumulated depreciation and amortization		(1,057	)		(414	)
Property, plant and equipment, net	$	557		$	860

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2018

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following:

	As of December 31,
($ in thousands)	2018		2017
Accrued expenses:
Accrued compensation	$	5,011	$	4,518
Accrued clinical trial expenses		3,561		442
Accrued professional fees and other		1,107		1,179
Total accrued expenses	$	9,679	$	6,139

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Schedule Of Share Based Compensation Stock Options Activity

The following table summarizes the stock option activity and related information:

	Number of Shares			Weighted Average Exercise Price		Total Intrinsic Value (in thousands)
Outstanding as of December 31, 2016		4,457,251		$	7.14	$	23,258
Granted		706,800		$	24.16	$	15,792
Exercised		(353,612	)	$	7.03		-
Forfeited		(258,620	)	$	9.51		-
Outstanding as of December 31, 2017		4,551,819		$	9.66	$	162,002
Granted		998,603			44.19		-
Exercised		(775,224	)		7.34		31,134
Forfeited		(138,053	)		18.71		3,195
Outstanding as of December 31, 2018		4,637,145		$	17.21	$	48,179
Options vested and exercisable		3,077,195		$	9.21	$	42,503

Schedule of Restricted Stock Number of units

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

	Number of units			Weighted average grant price
Unvested as of December 31, 2016		-		$	-
Granted		120,000			44.28
Unvested as of December 31, 2017		120,000		$	44.28
Granted		456,559			35.54
Vested and Settled		(938	)		49.14
Forfeited		(7,616	)		49.14
Unvested as of December 31, 2018		568,005	(1)	$	37.18

(1) Includes 128,332 RSUs that have vested but are subject to deferred settlement.

Assumptions for Weighted Average Fair Value of Options Granted

	Year Ended December 31,
	2018	2017	2016
Exercise price	$23.78 - $57.53	$12.81 - $44.28	$5.84 - $13.21
Expected volatility	75.6% - 86.1%	81.2% - 87.0%	85.8% - 91.8%
Risk-free rate of interest	2.56% - 3.04%	2.02% - 2.29%	1.36% - 2.18%
Expected term (years)	5.5 - 7.0	5.5 - 7.0	5.3 - 7.0
Expected dividend yield	-	-	-

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

The Company recognized stock-based compensation expense in continuing operations as follows:

	Year Ended December 31,
($ in thousands)	2018		2017		2016
Research and development	$	11,820	$	5,423	$	3,025
General and administrative		16,665		3,178		1,999
Total	$	28,485	$	8,601	$	5,024

Collaboration Agreement (Tables)

12 Months Ended

Dec. 31, 2018

Collaboration Agreement [Abstract]

Contract with Customer, Asset and Liability [Table Text Block]

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
Year ended December 31, 2018
Contract liabilities:
Deferred revenue	$	45,785	$	—	$	(5,125	)	$	40,660

Schedule of Collaboration revenue recognized with the period

	Year Ended
	December 31,
($ in thousands)	2018
Collaboration revenue recognized in the period from:
Amounts included in deferred revenue at the beginning of the period	$	5,125
Performance obligations satisfied in previous period		—

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Federal Income Tax Note

The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows:

	As of December 31,
	2018			2017			2016
Statutory federal income tax rate		(21.0	)%		(34.0	)%		(34.0	)%
State taxes, net of federal tax benefit		(7.1	)		(2.6	)		(4.3	)
Stock based compensation		(6.7	)		-			3.4
Credits		(2.4	)		(2.1	)		(1.8	)
Effective change in enacted tax rates		-			47.7			-
State rate change		(2.5	)		0.2			7.5
Other		(0.4	)		0.3			2.3
Change in valuation allowance		41.3			(27.0	)		25.5
Income taxes provision (benefit)		1.2	%		(17.5	)%		(1.4	)%

Schedule of Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and (liabilities) are as follows:

	As of December 31,
($ in thousands)	2018			2017
Deferred tax assets:
Federal and state-operating loss carryforwards	$	58,668		$	43,577
Stock-based compensation		14,023			5,726
Intangible assets		2,282			2,259
Deferred revenue		11,409			11,064
Research and development credits		5,472			5,604
Other		575			360
Total deferred tax assets		92,429			68,590
Valuation allowance		(87,543	)		(63,718	)
Deferred tax asset, net of allowance	$	4,886		$	4,872
In-process research and development		(8,138	)		(7,008	)
Net deferred tax liability	$	(3,252	)	$	(2,136	)

Schedule of Unrecognized Tax Benefits Roll Forward

The following table summarizes activity related to the Company’s gross unrecognized tax benefits (in thousands):

	Total
Balances as of December 31, 2016	$	-
Increases related to prior year tax positions		-
Increases related to 2017 tax positions		-
Balances as of December 31, 2017	$	-
Increases related to prior year tax positions		3,679
Increases related to 2018 tax positions		934
Balances as of December 31, 2018	$	4,613

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Rental Payments for Operating Leases

Future minimum lease payments under noncancelable operating leases are as follows:

2019	$	5,032
2020		4,537
2021		4,055
2022		4,075
2023		4,095
Total	$	21,794

Selected Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information

The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented.

($ in thousands except for per share amounts)	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
2018
Collaboration revenue	$	3,565		$	3,218		$	4,286		$	3,735
Operating expenses	$	20,237		$	30,384		$	26,861		$	30,057
Interest and other income	$	446		$	453		$	1,116		$	1,069
Unrealized loss from marketable securities, net of tax	$	(23	)	$	(127	)	$	(82	)	$	231
Net loss	$	(16,249	)	$	(26,806	)	$	(21,535	)	$	(26,161	)
Basic and diluted net loss per common share	$	(0.80	)	$	(1.30	)	$	(0.87	)	$	(1.03	)

2017
Collaboration revenue	$	684		$	2,359		$	2,660		$	3,315
Operating expenses	$	14,614		$	15,927		$	15,110		$	15,595
Interest and other income	$	136		$	240		$	241		$	366
Unrealized loss from marketable securities, net of tax	$	(137	)	$	(341	)	$	(99	)	$	(38	)
Net loss	$	(13,931	)	$	(13,599	)	$	(12,272	)	$	(3,007	)
Basic and diluted net loss per common share	$	(0.81	)	$	(0.78	)	$	(0.71	)	$	(0.16	)

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	$ 39,345	$ 1,663
Short-term investments:
Investments, Fair Value Disclosure	176,609	37,914
Long-term investments:
Investments, Fair Value Disclosure		3,347
Total assets measured at fair value	215,954	42,924
U.S. and foreign corporate debt securities [Member]
Long-term investments:
Investments, Fair Value Disclosure		3,347
Money Market Funds [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	39,345	1,663
Commercial Paper [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure
Short-term investments:
Investments, Fair Value Disclosure	55,136
Corporate Debt Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	73,159	37,914
Asset-backed Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	28,419
US Treasury Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	19,895
Fair Value, Inputs, Level 1 [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	39,345	1,663
Short-term investments:
Investments, Fair Value Disclosure	0	0
Long-term investments:
Investments, Fair Value Disclosure		0
Total assets measured at fair value	39,345	1,663
Fair Value, Inputs, Level 1 [Member] \| U.S. and foreign corporate debt securities [Member]
Short-term investments:
Investments, Fair Value Disclosure		0
Long-term investments:
Investments, Fair Value Disclosure		0
Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	39,345	1,663
Fair Value, Inputs, Level 1 [Member] \| Commercial Paper [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	0
Short-term investments:
Investments, Fair Value Disclosure	0
Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	0
Fair Value, Inputs, Level 1 [Member] \| Asset-backed Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	0
Fair Value, Inputs, Level 1 [Member] \| US Treasury Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	0
Fair Value, Inputs, Level 2 [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure		0
Short-term investments:
Investments, Fair Value Disclosure	176,609	37,914
Long-term investments:
Investments, Fair Value Disclosure		3,347
Total assets measured at fair value	176,609	41,261
Fair Value, Inputs, Level 2 [Member] \| U.S. and foreign corporate debt securities [Member]
Long-term investments:
Investments, Fair Value Disclosure		3,347
Fair Value, Inputs, Level 2 [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member] \| Commercial Paper [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	0
Short-term investments:
Investments, Fair Value Disclosure	55,136
Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	73,159	37,914
Fair Value, Inputs, Level 2 [Member] \| Asset-backed Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	28,419
Fair Value, Inputs, Level 2 [Member] \| US Treasury Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	19,895
Fair Value, Inputs, Level 3 [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure		0
Short-term investments:
Investments, Fair Value Disclosure	0	0
Long-term investments:
Investments, Fair Value Disclosure		0
Total assets measured at fair value	0	0
Fair Value, Inputs, Level 3 [Member] \| U.S. and foreign corporate debt securities [Member]
Long-term investments:
Investments, Fair Value Disclosure		0
Fair Value, Inputs, Level 3 [Member] \| Money Market Funds [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member] \| Commercial Paper [Member]
Cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	0
Short-term investments:
Investments, Fair Value Disclosure	0
Fair Value, Inputs, Level 3 [Member] \| Corporate Debt Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	0	$ 0
Fair Value, Inputs, Level 3 [Member] \| Asset-backed Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	0
Fair Value, Inputs, Level 3 [Member] \| US Treasury Securities [Member]
Short-term investments:
Investments, Fair Value Disclosure	$ 0

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Details 1) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	5,241,929	4,687,115	4,474,160
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	16,909
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	4,637,145	4,551,819	4,457,251
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	21,483
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	568,005	120,000	0

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	34.00%	34.00%
Share Based Compensation Arrangement By Share Based Payment Award Forfeiture Rate	0.00%
Maximum [Member]
Property, Plant and Equipment, Useful Life	7 years
Operating Lease, Liability	$ 0
Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Operating Lease, Liability	$ 0

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

Dec. 31, 2018

Dec. 31, 2017

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

Amortized Cost

$ 176,735

$ 41,449

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

(126)

(194)

Fair Value

176,609

41,261

Short-term Investments [Member] | Corporate Bond Securities [Member]

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

Amortized Cost

101,701

38,092

Gross Unrealized Gain

^[1]

Gross Unrealized Loss

^[1]

(122)

(184)

Fair Value

101,579

37,914

Short-term Investments [Member] | 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 Investments [Member] | 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

Long-term Investments [Member] | Corporate Bond Securities [Member]

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

Amortized Cost

3,357

Gross Unrealized Loss

^[1]

(10)

Fair Value

$ 3,347

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

Investments in Marketable Securities - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Proceeds from Sale of Available-for-sale Securities	$ 48,900	$ 33,500	$ 44,300
Marketable Securities, Realized Gain (Loss)	$ 0	$ (615)	$ (1,140)
Short-term Investments [Member]
Available For Sale Securities Maturity Term	less than one year

Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 1,614	$ 1,274
Less: Accumulated depreciation and amortization	(1,057)	(414)
Property, plant and equipment, net	557	860
Computer hardware and software [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	194	105
Lab equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	407	370
Office equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	70	25
Leasehold improvement [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	790	774
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 153	$ 0

Property, Plant and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation	$ 643	$ 219	$ 80

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued expenses:
Accrued compensation	$ 5,011	$ 4,518
Accrued clinical trial expenses	3,561	442
Accrued professional fees and other	1,107	1,179
Total accrued expenses	$ 9,679	$ 6,139

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		12 Months Ended
	Nov. 06, 2017	Jul. 16, 2018	Nov. 02, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2018	Dec. 29, 2017
Stockholders Equity Note [Line Items]
Proceeds from Issuance Initial Public Offering				$ 155,425	$ 64,847	$ 0
Initial Public Offering Value Of Shares Authorized								$ 250,000
Common Stock, Par or Stated Value Per Share				$ 0.001	$ 0.001		$ 0.001
Common Stock, Shares Authorized				100,000,000	50,000,000		100,000,000
Preferred Stock, Shares Authorized				5,000,000	5,000,000
Common Stock [Member]
Stockholders Equity Note [Line Items]
Net proceeds raised from common stock issued in a public offering			$ 64,800
Stock Issued During Period, Shares, New Issues	2,541,000		331,500
Public Offering [Member]
Stockholders Equity Note [Line Items]
Stock Issued During Period, Shares, New Issues		4,600,000
Sale of Stock, Price Per Share		$ 36.00
Proceeds from Issuance Initial Public Offering		$ 155,400
Additional Shares Of Common Stock Issued		600,000
Underwriters [Member] \| Common Stock [Member]
Stockholders Equity Note [Line Items]
Stock Issued During Period, Shares, New Issues			331,500
Investors [Member] \| Common Stock [Member]
Stockholders Equity Note [Line Items]
Stock Issued During Period, Shares, New Issues	2,541,000
Sale of Stock, Price Per Share	$ 27.25
Maximum [Member] \| At the Market Offerings [Member]
Stockholders Equity Note [Line Items]
Initial Public Offering Value Of Shares Authorized								$ 75,000

Stock-Based Compensation (Details) - Stock Option [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Option, Outstanding at beginning of period	4,551,819	4,457,251
Option, Granted	998,603	706,800
Option, Exercised	(775,224)	(353,612)
Option, Forfeited	(138,053)	(258,620)
Option, Outstanding at end of period	4,637,145	4,551,819
Options vested and exercisable	3,077,195
Weighted Average Exercise Price
Option, Outstanding at beginning of period	$ 9.66	$ 7.14
Option, Granted	44.19	24.16
Option, Exercised	7.34	7.03
Option, Forfeited	18.71	9.51
Option, Outstanding at end of period	17.21	$ 9.66
Options vested and exercisable	$ 9.21
Total Intrinsic Value
Option, Outstanding at beginning of period	$ 162,002	$ 23,258
Option, Granted	0	15,792
Option, Exercised	31,134	0
Option, Forfeited	3,195	0
Option, Outstanding at end of period	48,179	$ 162,002
Options vested and exercisable	$ 42,503

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

12 Months Ended

Dec. 31, 2018

Dec. 31, 2017

Beginning of period

120,000

Number of units Granted

456,559

120,000

Number of units Vested and Settled

(938)

Number of units Forfeited

(7,616)

Ending of period

568,005

^[1]

120,000

Beginning of period

$ 44.28

$ 0

Weighted average grant price Granted

35.54

44.28

Weighted average grant price Vested and Settled

49.14

Weighted average grant price Forfeited

49.14

Ending of period

$ 37.18

$ 44.28

[1]	Includes 128,332 RSUs that have vested but are subject to deferred settlement.

Stock-Based Compensation (Details 2) - USD ($)	12 Months Ended
Stock-Based Compensation (Details 2) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected dividend yield	$ 0	$ 0	$ 0
Maximum [Member]
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Exercise price	$ 57.53	$ 44.28	$ 13.21
Expected stock price volatility	86.10%	87.00%	91.80%
Risk-free rate of interest	3.04%	2.29%	2.18%
Expected term (years)	7 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	$ 23.78	$ 12.81	$ 5.84
Expected stock price volatility	75.60%	81.20%	85.80%
Risk-free rate of interest	2.56%	2.02%	1.36%
Expected term (years)	5 years 6 months	5 years 6 months	5 years 3 months 18 days

Stock-Based Compensation (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Allocated Share-based Compensation Expense	$ 28,485	$ 8,601	$ 5,024
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Allocated Share-based Compensation Expense	11,820	5,423	3,025
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Allocated Share-based Compensation Expense	$ 16,665	$ 3,178	$ 1,999

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

1 Months Ended

12 Months Ended

Nov. 14, 2018

Nov. 30, 2018

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Nov. 29, 2018

May 30, 2018

Stock Issued During Period, Value, Employee Stock Purchase Plan

$ 21,483

$ 408,000

Common Stock, Capital Shares Reserved for Future Issuance

1,900,000

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

6 years 2 months 12 days

Share-based Compensation

$ 28,485,000

$ 8,601,000

$ 5,024,000

Estimated Stock Based Compensation

$ 19,400,000

Common Stock Shares Subscribed Under Employee Stock Purchase Plan

21,483

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

7 years 1 month 6 days

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

85.00%

Class of Warrant or Right, Outstanding

15,296

Warrant to Purchase of Common Stock

1,613

Warrant Maturity Term

1 year 8 months 12 days

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

7 years 1 month 6 days

Class of Warrant or Right, Exercise Price of Warrants or Rights

$ 30.00

Warrant [Member]

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

1 year 8 months 12 days

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

1 year 8 months 12 days

2018 Employee Stock Purchase Plan 2018 [Member]

Common Stock, Capital Shares Reserved for Future Issuance

378,517

Stock Issued During Period, Shares, New Issues

400,000

Share-based Compensation

$ 200,000

Maximum Number of Common Stock to be Issued per Offering

1,000

Percentage of Payroll Deductions in ESPP

15.00%

Employee Stock [Member]

Share Price

$ 19.00

Stock Appreciation Rights (SARs) [Member]

Accrued Employee Benefits

$ 39,000

Restricted Stock [Member]

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

9 years 2 months 12 days

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

$ 10,400,000

Restricted Stock Units (RSUs) [Member]

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

568,005

^[1]

120,000

Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number

128,332

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

$ 2,400,000

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

$ 1,900,000

[1]	Includes 128,332 RSUs that have vested but are subject to deferred settlement.

Collaboration Agreement (Details) - Deferred revenue [Member]	12 Months Ended
	Dec. 31, 2018 USD ($)
Change In Contract With Customer Liability [Line Items]
Balance at Beginning of Period	$ 45,785
Additions	0
Deductions	(5,125)
Balance at End of Period	$ 40,660

Collaboration Agreement (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Collaboration revenue recognized in the period from:
Amounts included in deferred revenue at the beginning of the period	$ 5,100	$ 5,229
Performance obligations satisfied in previous period	$ 0

Collaboration Agreement - Additional Information (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended								12 Months Ended
	Feb. 10, 2017	Feb. 28, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred Revenue Amortization Period Over Service Tenure											10 years
Revenue from Contract with Customer, Including Assessed Tax	$ 50,000		$ 3,735	$ 4,286	$ 3,218	$ 3,565	$ 3,315	$ 2,660	$ 2,359	$ 684	$ 14,804	$ 9,019	$ 0
Accounts Receivable, Net, Current			2,430				2,274				2,430	2,274
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			5,100				5,200				5,100	5,200
Contract with Customer, Liability, Noncurrent			$ 35,600				$ 40,600				35,600	40,600
Cost Of Reimbursable Expenses											14,800	$ 9,000
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) - Indiana University Research and Technology Corporation [Member] - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Potential Milestone Payments	$ 800,000
Payment of Milestone	$ 100,000	$ 0	$ 0

Income Taxes (Details)	12 Months Ended
Income Taxes (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax [Line Items]
Statutory federal income tax rate	(21.00%)	(34.00%)	(34.00%)
State taxes, net of federal tax benefit	(7.10%)	(2.60%)	(4.30%)
Stock based compensation	(6.70%)	0.00%	3.40%
Credits	(2.40%)	(2.10%)	(1.80%)
Effective change in enacted tax rates	0.00%	47.70%	0.00%
State rate change	(2.50%)	0.20%	7.50%
Other	(0.40%)	0.30%	2.30%
Change in valuation allowance	41.30%	(27.00%)	25.50%
Income taxes provision (benefit)	1.20%	(17.50%)	(1.40%)

Income Taxes (Details 1) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Federal and state-operating loss carryforwards	$ 58,668	$ 43,577
Stock-based compensation	14,023	5,726
Intangible assets	2,282	2,259
Deferred revenue	11,409	11,064
Research and development credits	5,472	5,604
Other	575	360
Total deferred tax assets	92,429	68,590
Valuation allowance	(87,543)	(63,718)
Deferred tax asset, net of allowance	4,886	4,872
In-process research and development	(8,138)	(7,008)
Net deferred tax liability	$ (3,252)	$ (2,136)

Income Taxes (Details 2) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details 2) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Balances Beginning	$ 0	$ 0
Increases related to prior year tax positions	3,679	0
Increases related to tax positions	934	0
Balances Ending	$ 4,613	$ 0

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Deferred Tax Assets, Net of Valuation Allowance, Current		$ 4,900
Statutory Federal tax rate	21.00%	34.00%	34.00%
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	$ 209,000
Deferred Tax Assets, Operating Loss Carryforwards, Federal	209,200
Deferred Income Tax Expense (Benefit)	1,099	$ (9,050)	$ (618)
Increase (Decrease) in Deferred Income Taxes	24,700
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	28,400
Increase (Decrease) in Income Taxes	$ 3,700
Operating Loss Carryforwards, Limitations on Use	The Tax Act also permits an indefinite carry forward of net operating losses generated in taxable years ending after December 31, 2017, subject to a utilization limitation of 80% of taxable income.
Income Tax Expense (Benefit)	$ 1,099	(9,050)	$ (618)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		$ 8,600
Domestic Tax Authority [Member]
Income Taxes [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Research	3,600
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration	94,700
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	114,500
California Franchise Tax Board [Member]
Income Taxes [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 1,900
Scenario, Plan [Member]
Income Taxes [Line Items]
Statutory Federal tax rate	34.00%
Maximum [Member] \| Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating Loss Carry forwards Expiration Period	2038
Maximum [Member] \| State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating Loss Carry forwards Expiration Period	2038
Minimum [Member] \| Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating Loss Carry forwards Expiration Period	2027
Minimum [Member] \| State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating Loss Carry forwards Expiration Period	2027

Commitments and Contingencies (Details)	Dec. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Line Items]
2019	$ 5,032
2020	4,537
2021	4,055
2022	4,075
2023	4,095
Total	$ 21,794

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Line Items]
Operating Leases, Rent Expense	$ 4.2	$ 2.1	$ 1.9

Employee Benefit Plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 700,000	$ 0	$ 0

Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	Feb. 10, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaboration revenue	$ 50,000	$ 3,735	$ 4,286	$ 3,218	$ 3,565	$ 3,315	$ 2,660	$ 2,359	$ 684	$ 14,804	$ 9,019	$ 0
Operating expenses		30,057	26,861	30,384	20,237	15,595	15,110	15,927	14,614	107,539	61,246	45,278
Interest and other income		1,069	1,116	453	446	366	241	240	136	3,083	983	1,539
Unrealized loss from marketable securities, net of tax		231	(82)	(127)	(23)	(38)	(99)	(341)	(137)
Net loss		$ (26,161)	$ (21,535)	$ (26,806)	$ (16,249)	$ (3,007)	$ (12,272)	$ (13,599)	$ (13,931)	$ (90,751)	$ (42,809)	$ (44,261)
Basic and diluted net loss per common share		$ (1,030)	$ (870)	$ (1,300)	$ (800)	$ (160)	$ (710)	$ (780)	$ (810)	$ (3.98)	$ (2.41)	$ (2.57)

- Definition

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

+ References + Details