Assembly Biosciences (ASMB) 10-Q 5 Aug 20 2020 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Aug. 03, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2020
Entity File Number	001-35005
Entity Registrant Name	ASSEMBLY BIOSCIENCES, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-8729264
Entity Address, Address Line One	331 Oyster Point Blvd.
Entity Address, Address Line Two	Fourth Floor
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	833
Local Phone Number	509-4583
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Central Index Key	0001426800
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Trading Symbol	ASMB
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, par value $0.001
Entity Common Stock, Shares Outstanding		32,854,914
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	true

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 96,709	$ 46,732
Marketable securities	130,005	227,311
Accounts receivable from collaboration	3,315	3,374
Prepaid expenses and other current assets	5,059	5,363
Total current assets	235,088	282,780
Property and equipment, net	2,063	1,830
Operating lease right-of-use (ROU) assets	10,780	11,975
Other assets	5,232	1,684
Indefinite-lived intangible asset	29,000	29,000
Goodwill	12,638	12,638
Total assets	294,801	339,907
Current liabilities
Accounts payable	3,640	1,731
Accrued clinical expenses	4,362	4,826
Other accrued expenses	6,019	8,286
Deferred revenue - short-term		6,411
Operating lease liabilities - short-term	3,250	3,186
Total current liabilities	17,271	24,440
Deferred tax liabilities	2,531	2,531
Deferred revenue - long-term		30,637
Operating lease liabilities - long-term	7,884	9,082
Total liabilities	27,686	66,690
Commitments and contingencies
Stockholders' equity
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 100,000,000 shares authorized as of June 30, 2020 and December 31, 2019; 32,807,519 and 32,558,307 shares issued and outstanding as of June 30, 2020 and December 31, 2019, respectively	33	32
Additional paid-in capital	725,784	712,807
Accumulated other comprehensive income (loss)	104	(201)
Accumulated deficit	(458,806)	(439,421)
Total stockholders' equity	267,115	273,217
Total liabilities and stockholders' equity	$ 294,801	$ 339,907

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	32,807,519	32,558,307
Common stock, shares outstanding	32,807,519	32,558,307

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Collaboration revenue	$ 39,376	$ 3,080	$ 43,457	$ 6,966
Operating expenses:
Research and development	23,327	18,700	46,373	41,405
General and administrative	9,470	4,080	18,199	13,597
Total operating expenses	32,797	22,780	64,572	55,002
Income (loss) from operations	6,579	(19,700)	(21,115)	(48,036)
Other income
Interest and other income, net	691	1,186	1,730	2,463
Total other income	691	1,186	1,730	2,463
Income (loss) before income taxes	7,270	(18,514)	(19,385)	(45,573)
Income tax benefit		11		18
Net income (loss)	7,270	(18,503)	(19,385)	(45,555)
Other comprehensive income
Unrealized gain on marketable securities, net of tax	190	52	305	160
Comprehensive income (loss)	$ 7,460	$ (18,451)	$ (19,080)	$ (45,395)
Net income (loss) per share, basic	$ 0.21	$ (0.72)	$ (0.55)	$ (1.77)
Weighted average common shares outstanding, basic	35,307,669	25,740,500	35,229,570	25,690,617
Net income (loss) per share, diluted	$ 0.19	$ (0.72)	$ (0.55)	$ (1.77)
Weighted average common shares outstanding, diluted	37,291,474	25,740,500	35,229,570	25,690,617

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (19,385)	$ (45,555)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	237	260
Stock-based compensation	12,058	8,645
Net accretion and amortization of investments in marketable debt securities	(101)	(1,141)
Non-cash rent expense	2,308	2,208
Deferred income tax benefit	0	(18)
Loss on disposal of fixed assets	0	102
Other	0	(5)
Changes in operating assets and liabilities:
Accounts receivable from collaboration	59	(473)
Prepaid expenses and other current assets	304	(5,068)
Other assets	(2,155)	1,655
Accounts payable	516	(279)
Accrued clinical expenses	(464)	248
Other accrued expenses	(2,416)	(2,428)
Deferred revenue	(37,048)	(996)
Operating lease liabilities	(2,247)	(2,099)
Net cash used in operating activities	(48,334)	(44,944)
Cash flows from investing activities
Purchases of property and equipment	(470)	(1,539)
Purchases of marketable securities	(44,240)	(93,667)
Proceeds from maturities of marketable securities	119,252	131,591
Proceeds from sale of marketable securities	22,700	500
Net cash provided by investing activities	97,242	36,885
Cash flows from financing activities
Proceeds from the exercise of stock options	602	331
Proceeds from the issuance of common stock under Employee Stock Purchase Plan (ESPP)	467	515
Net cash provided by financing activities	1,069	846
Net increase (decrease) in cash and cash equivalents	49,977	(7,213)
Cash and cash equivalents at the beginning of the period	46,732	41,471
Cash and cash equivalents at the end of the period	96,709	34,258
Supplemental non-cash investing and financing activities
Operating lease liabilities arising from obtaining ROU assets	$ 545	$ 14,225

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2018	$ 210,653	$ 25	$ 552,762	$ (347)	$ (341,787)
Balance (in shares) at Dec. 31, 2018		25,495,425
Issuance of common stock upon exercise of stock options	331		331
Issuance of common stock upon exercise of stock options (in shares)		50,875
Issuance of common stock under ESPP	515		515
Issuance of common stock under ESPP (in shares)		36,804
Issuance of shares of common stock for settlement of restricted stock units (RSUs)		$ 1	(1)
Issuance of shares of common stock for settlement of restricted stock units (RSUs) (in shares)		63,679
Settlement of RSUs for cash	(4)		(4)
Unrealized gain on marketable debt securities, net of tax	160			160
Stock-based compensation	8,607		8,607
Net loss	(45,555)				(45,555)
Balance at Jun. 30, 2019	174,707	$ 26	562,210	(187)	(387,342)
Balance (in shares) at Jun. 30, 2019		25,646,783
Balance at Mar. 31, 2019	190,401	$ 26	559,453	(239)	(368,839)
Balance (in shares) at Mar. 31, 2019		25,549,757
Issuance of common stock upon exercise of stock options	191		191
Issuance of common stock upon exercise of stock options (in shares)		29,875
Issuance of common stock under ESPP	515		515
Issuance of common stock under ESPP (in shares)		36,804
Issuance of shares of common stock for settlement of restricted stock units (RSUs) (in shares)		30,347
Unrealized gain on marketable debt securities, net of tax	52			52
Stock-based compensation	2,051		2,051
Net loss	(18,503)				(18,503)
Balance at Jun. 30, 2019	174,707	$ 26	562,210	(187)	(387,342)
Balance (in shares) at Jun. 30, 2019		25,646,783
Balance at Dec. 31, 2019	273,217	$ 32	712,807	(201)	(439,421)
Balance (in shares) at Dec. 31, 2019		32,558,307
Issuance of common stock upon exercise of stock options	602	$ 1	601
Issuance of common stock upon exercise of stock options (in shares)		91,713
Issuance of common stock under ESPP	467		467
Issuance of common stock under ESPP (in shares)		42,266
Issuance of shares of common stock for settlement of restricted stock units (RSUs) (in shares)		115,233
Unrealized gain on marketable debt securities, net of tax	305			305
Stock-based compensation	11,909		11,909
Net loss	(19,385)				(19,385)
Balance at Jun. 30, 2020	267,115	$ 33	725,784	104	(458,806)
Balance (in shares) at Jun. 30, 2020		32,807,519
Balance at Mar. 31, 2020	251,768	$ 32	717,898	(86)	(466,076)
Balance (in shares) at Mar. 31, 2020		32,624,725
Issuance of common stock upon exercise of stock options	483	$ 1	482
Issuance of common stock upon exercise of stock options (in shares)		74,879
Issuance of common stock under ESPP	467		467
Issuance of common stock under ESPP (in shares)		42,266
Issuance of shares of common stock for settlement of restricted stock units (RSUs) (in shares)		65,649
Unrealized gain on marketable debt securities, net of tax	190			190
Stock-based compensation	6,937		6,937
Net loss	7,270				7,270
Balance at Jun. 30, 2020	$ 267,115	$ 33	$ 725,784	$ 104	$ (458,806)
Balance (in shares) at Jun. 30, 2020		32,807,519

Nature of Business

Nature of Business	6 Months Ended
	Jun. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	Note 1 - Nature of Business Overview Assembly Biosciences, Inc., together with its subsidiaries (Assembly or the Company), incorporated in Delaware in October 2005, is a clinical-stage biotechnology company advancing two innovative programs: a novel class of oral therapeutic candidates targeting chronic hepatitis B virus (HBV) infection and a novel class of oral live microbial biotherapeutic candidates, which are designed to treat disorders associated with the microbiome. The Company operates in one segment and is headquartered in South San Francisco, California, with operations in California, Connecticut and China. The Company’s HBV Cure program is pursuing multiple drug candidates that inhibit the HBV lifecycle and block the generation of covalently closed circular DNA (cccDNA), with the aim of increasing the current low cure rates for patients with chronic HBV infection. Assembly has discovered several novel core inhibitors, which are small molecules that directly target and allosterically modify the HBV core protein. The Company’s Microbiome program is centered on a fully integrated platform that includes a biological function-based strain isolation, identification, characterization and selection process, methods for strain purification and growth under conditions compliant with current Good Manufacturing Practice (cGMP) requirements. That platform is complemented by a licensed patented delivery system that the Company calls GEMICEL®, which is designed to allow for targeted oral delivery of live biologic and conventional therapies to the lower gastrointestinal (GI) tract. Using the Company’s microbiome platform, the Company is exploring product candidates for multiple disease indications, including ulcerative colitis (UC), Crohn’s disease and irritable bowel syndrome (IBS) in connection with its Research, Development, Collaboration and License Agreement (the Allergan Collaboration Agreement) with Allergan Pharmaceuticals International Limited (Allergan), which was acquired by AbbVie Inc. (AbbVie) in May 2020. In June 2020, AbbVie made a strategic portfolio decision to terminate the Allergan Collaboration Agreement effective on October 10, 2020 (see Note 8). Assembly is also exploring the microbiome in connection with immune-mediated and metabolic disorders and oncology. Liquidity The Company has not derived any revenue from product sales to date and currently has no approved products. Once a product has been developed, it will need to be approved for sale by the U.S. Food and Drug Administration (FDA) or an applicable foreign regulatory agency. Since inception, the Company’s operations have been financed primarily through the sale of equity securities, proceeds from the exercise of warrants and stock options, issuance of debt and an upfront payment related to the Allergan Collaboration Agreement. The Company has incurred losses from operations since inception and expects to continue to incur substantial losses for the next several years as it continues its product development efforts. Management believes the Company currently has sufficient funds to meet its operating requirements for at least the next 12 months following the date that these unaudited condensed consolidated interim financial statements are issued. If the Company cannot generate significant cash from its operations, it intends to obtain any additional funding it requires through strategic relationships, public or private equity or debt financings, grants or other arrangements (see Note 6 for recent sales of common stock). The Company cannot assure such funding will be available on reasonable terms, if at all. Market volatility resulting from the global novel coronavirus disease (COVID-19) pandemic or other factors could also adversely impact the Company’s ability to access capital when and as needed. If the Company is unable to generate sufficient revenue from its collaborations, secure additional sources of funding or receive full and timely collections of amounts due, it may be necessary to significantly reduce the current rate of spending through reductions in staff and delaying, scaling back, or stopping certain research and development programs, including more costly clinical trials.

Summary of Significant Accounti

Summary of Significant Accounting Policies and Recent Accounting Pronouncements	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Recent Accounting Pronouncements	Note 2 - Summary of Significant Accounting Policies and Recent Accounting Pronouncements Basis of Presentation The accompanying unaudited interim condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and pursuant to the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the U.S. Securities and Exchange Commission (SEC). In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements and include normal recurring adjustments necessary for the fair presentation of the Company’s financial position and its results of operations and comprehensive loss and its cash flows for the periods presented. These statements do not include all disclosures required by U.S. GAAP and should be read in conjunction with the Company’s audited consolidated financial statements and accompanying notes for the fiscal year ended December 31, 2019, which are contained in the Company’s Annual Report on Form 10-K as filed with the SEC on March 4, 2020. The results for the three and six months ended June 30, 2020 are not necessarily indicative of results to be expected for the entire year ending December 31, 2020 or future operating periods. Use of Estimates The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Significant estimates inherent in the preparation of the accompanying unaudited condensed consolidated financial statements include revenue recognition, clinical trial accruals, recoverability and useful lives (indefinite or finite) of intangible assets, assessment of impairment of goodwill, provisions for income taxes, amounts receivable and recognized as revenue under the Allergan Collaboration Agreement, measurement of operating lease liabilities, and the fair value of stock options, stock appreciation rights, and restricted stock units (RSUs) granted to employees, directors and consultants. The Company’s estimates could be affected by external conditions, including those unique to the Company and general economic conditions. It is reasonably possible that these external factors could have an effect on the Company’s estimates and could cause actual results to differ materially from those estimates and assumptions. Other Risks and Uncertainties In March 2020, the World Health Organization declared the COVID-19 outbreak a pandemic. To date, the Company’s operations have not been significantly impacted by the COVID-19 pandemic. However, the Company cannot at this time predict the specific extent, duration, or full impact the COVID-19 pandemic will have on its business, operations, strategy, prospects and financial condition and results. The impact of the COVID-19 pandemic on the financial performance of the Company will depend on future developments, including the duration and spread of the outbreak and related governmental advisories and restrictions. These developments and the impact of the COVID-19 pandemic on the financial markets and the overall economy are highly uncertain. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be adversely affected. Income Taxes In March 2020, the Families First Coronavirus Response Act (FFCR Act) and the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) were each enacted in response to the COVID-19 pandemic. The FFCR Act and the CARES Act contain numerous income tax provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. In June 2020, Assembly Bill 85 (A.B. 85) was signed into California law. A.B. 85 provides for a three-year three-year The FFCR Act, CARES Act and A.B. 85 did not have a material impact on the Company’s condensed consolidated financial statements as of June 30, 2020; however, the Company continues to examine the impacts the FFCR Act, CARES Act and A.B. 85 may have on its business, results of operations, financial condition and liquidity. Net Income (Loss) per Share Basic net income (loss) per common share excludes dilution and is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period. Diluted net income (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. In December 2019, the Company sold 6,287,878 shares of common stock as well as pre-funded warrants to purchase up to 2,424,242 shares of common stock (see Note 6). The pre-funded warrants are exercisable for shares of common stock at a price of $0.001 per share. The shares of common stock into which the pre-funded warrants may be exercised are considered outstanding for the purposes of computing earnings per share because the shares may be issued for little or no consideration, are fully vested, and are exercisable after the original issuance date. A reconciliation of the numerators and the denominators of the basic and diluted net income (loss) per common share computations is as follows (in thousands, except per share amounts): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Numerator: Net income (loss) 7,270 (18,503 ) (19,385 ) (45,555 ) Denominator: Shares used in per share calculation - basic 35,307,669 25,740,500 35,229,570 25,690,617 Dilutive effect of securities 1,983,805 - - - Shares used in per share calculation - diluted 37,291,474 25,740,500 35,229,570 25,690,617 Net income (loss) per share: Basic 0.21 (0.72 ) (0.55 ) (1.77 ) Diluted 0.19 (0.72 ) (0.55 ) (1.77 ) Securities excluded from the computation of diluted income (loss) per share because including them would have been antidilutive are as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Warrants to purchase common stock 15,296 15,296 15,296 15,296 Options to purchase common stock 3,521,778 5,203,935 6,652,076 5,203,935 Common stock subject to purchase under our ESPP 8,991 5,976 8,991 5,976 Unvested RSUs 41,762 489,857 978,879 489,857 Total 3,587,827 5,715,064 7,655,242 5,715,064 As of June 30, 2020, 145,000 performance-based RSUs granted by the Company were excluded from the table above because they are subject to contingencies that were not achieved as of this date. Adoption of Recent Accounting Pronouncements In January 2017, the Financial Accounting Standards Board (FASB) issued ASU 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment Financial Instruments – Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates On January 1, 2020, the Company adopted ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement, On January 1, 2020, the Company adopted ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes Recent Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments

Investments in Marketable Secur

Investments in Marketable Securities	6 Months Ended
	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Investments in Marketable Securities	Note 3 – Investments in Marketable Securities The carrying amounts of cash equivalents and marketable securities approximate their fair value based upon quoted market prices. Certain of the Company’s financial instruments are not measured at fair value on a recurring basis, but are recorded at amounts that approximate their fair value due to their liquid or short-term nature, such as cash, accounts receivable, accounts payable, accrued expenses, lease liability-short term and deferred revenue-short term. The Company uses the following three-level hierarchy that maximizes the use of observable inputs and minimizes the use of unobservable inputs to value its financial instruments: Level 1: Observable inputs such as unadjusted quoted prices in active markets for identical instruments. Level 2: Quoted prices for similar instruments that are directly or indirectly observable in the marketplace. Level 3: Significant unobservable inputs that are supported by little or no market activity and that are financial instruments whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant judgment or estimation. Investments in marketable securities consisted of the following (in thousands): June 30, 2020 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Cash equivalents Money market funds $ 94,524 $ — $ — $ 94,524 Total cash equivalents 94,524 — — 94,524 Short-term investments U.S. and foreign corporate debt securities 32,958 161 — 33,119 Asset-backed securities 22,183 72 — 22,255 U.S. treasury securities 36,080 176 — 36,256 U.S. and foreign commercial paper 38,375 — — 38,375 Total short-term investments 129,596 409 — 130,005 Total cash equivalents and investments $ 224,120 $ 409 $ — $ 224,529 December 31, 2019 Amortized Cost Gross Unrealized Gain (1) Gross Unrealized Loss (1) Fair Value Cash equivalents Money market funds $ 33,095 $ — $ — $ 33,095 U.S. and foreign corporate debt securities 5,000 — (1 ) 4,999 U.S. and foreign commercial paper 4,484 — — 4,484 Total cash equivalents 42,579 — (1 ) 42,578 Short-term investments U.S. and foreign corporate debt securities 72,452 38 (4 ) 72,486 Asset-backed securities 34,008 17 — 34,025 U.S. treasury securities 44,692 24 (2 ) 44,714 U.S. and foreign commercial paper 76,086 — — 76,086 Total short-term investments 227,238 79 (6 ) 227,311 Total cash equivalents and investments $ 269,817 $ 79 $ (7 ) $ 269,889 (1) Gross unrealized gain (loss) is pre-tax. The contractual term to maturity of short-term marketable securities held by the Company as of June 30, 2020 is less than one year. There were no long-term marketable securities held by the Company as of June 30, 2020. Realized gains and losses for the three and six months ended June 30, 2020 and 2019 were not significant. None of the Company’s investments have been in a continuous unrealized loss position for more than 12 months as of June 30, 2020. The following tables present the fair value of the Company’s financial assets measured at fair value on a recurring basis (in thousands): June 30, 2020 Level 1 Level 2 Level 3 Fair Value Cash equivalents Money market fund $ 94,524 $ — $ — $ 94,524 Total cash equivalents 94,524 — — 94,524 Short-term investments U.S. and foreign corporate debt securities — 33,119 — 33,119 Asset-backed securities — 22,255 — 22,255 U.S. treasury securities — 36,256 — 36,256 U.S. and foreign commercial paper — 38,375 — 38,375 Total short-term investments — 130,005 — 130,005 Total assets measured at fair value $ 94,524 $ 130,005 $ — $ 224,529 December 31, 2019 Level 1 Level 2 Level 3 Fair Value Cash equivalents Money market fund 33,095 — — 33,095 U.S. and foreign corporate debt securities — 4,999 — 4,999 U.S. and foreign commercial paper — 4,484 — 4,484 Total cash equivalents 33,095 9,483 — 42,578 Short-term investments U.S. and foreign corporate debt securities — 72,486 — 72,486 Asset-backed securities — 34,025 — 34,025 U.S. treasury securities — 44,714 — 44,714 U.S. and foreign commercial paper — 76,086 — 76,086 Total short-term investments — 227,311 — 227,311 Total assets measured at fair value $ 33,095 $ 236,794 $ — $ 269,889 The Company estimates the fair value of its U.S. and foreign corporate debt securities, asset-backed securities, U.S. treasury securities and U.S. and foreign commercial paper by taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data, and other observable inputs. There were no transfers between Level 1, Level 2 or Level 3 during the periods presented.

Property and Equipment, Net

Property and Equipment, Net	6 Months Ended
	Jun. 30, 2020
Property Plant And Equipment [Abstract]
Property and Equipment, Net	Note 4 - Property and Equipment, Net Property and equipment consist of the following (in thousands): Useful life June 30, December 31, (Years) 2020 2019 Lab equipment 3 to 5 $ 290 $ 247 Office equipment 7 699 699 Leasehold improvement 1 to 5 2,084 2,084 Total property and equipment 3,073 3,030 Less: Accumulated depreciation and amortization (1,437 ) (1,200 ) Construction in progress N/A 427 — Property and equipment, net $ 2,063 $ 1,830 Depreciation expense was $0.1 million and $0.2 million for the three and six months ended June 30, 2020, respectively and $0.1 million and $0.3 million for the three and six months ended June 30, 2019, respectively and was recorded in both research and development expense and general and administrative expense in the unaudited condensed consolidated statements of operations and comprehensive loss. Primarily all of property and equipment of the Company is located in the U.S.

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2020
Payables And Accruals [Abstract]
Accrued Expenses	Note 5 – Accrued Expenses Accrued expenses consist of the following (in thousands): June 30, December 31, 2020 2019 Accrued expenses: Accrued compensation $ 4,186 $ 5,312 Accrued restructuring charges 1,019 2,094 Accrued professional fees and other 814 880 Total accrued expenses $ 6,019 $ 8,286 Accrued restructuring charges relate to the Company’s decision to relocate its headquarters to South San Francisco, California as approved by the Board of Directors in November 2019 and effective January 1, 2020. The Company accrued restructuring charges of $2.1 million in 2019 related to one-time severance payments and other employee-related costs associated with the relocation plan. This represents the total amount expected to be incurred in connection with the relocation and is expected to be fully paid in 2020.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Stockholders' Equity	Note 6 – Stockholders’ Equity The Company is authorized to issue 5,000,000 shares of preferred stock as of June 30, 2020 and December 31, 2019, respectively. As of June 30, 2020 and December 31, Sale of Common Stock and Pre-Funded Warrants In December 2017, the Company filed a registration statement on Form S-3 with the SEC using a “shelf” registration statement, file No. 333-222366, which became effective January 10, 2018 (the Registration Statement). Under this shelf registration process, the Company may from time to time sell any combination of the securities described in the Registration Statement in one or more offerings up to an aggregate offering price of $250.0 million. In connection with the filing of this Registration Statement, the Company entered into a sales agreement under which the Company may offer and sell shares of its common stock having an aggregate offering price of up to $75.0 million through “at the market offerings” (ATM). As of June 30, 2020, no shares have been sold under the ATM program and $21.4 million remains available for sale under this Registration Statement. In December 2019, the Company sold to various investors an aggregate of 6,287,878 shares of common stock at a public offering price of $16.50 per share, which included the exercise in full by the underwriters of their option to purchase 1,136,363 additional shares of common stock, and pre-funded warrants to purchase 2,424,242 shares of common stock at a public offering price of $16.499 per warrant. The Company received aggregate net proceeds of $134.7 million from the offering and the option exercise, after deducting underwriting discounts and commissions and offering expenses payable by the Company. The pre-funded warrants became immediately exercisable upon issuance at an exercise price of $0.001 per share, but under their terms, the outstanding pre-funded warrants to purchase shares of the Company’s common stock generally may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99% following such exercise. The exercise price and number of shares of common stock issuable upon the exercise of the pre-funded warrants (Warrant Shares) are subject to adjustment in the event of any stock dividends and splits, reverse stock split, recapitalization, reorganization or similar transaction, as described in the pre-funded warrant agreements. Under certain circumstances, the pre-funded warrants may be exercisable on a “cashless” basis. Both the pre-funded warrants and the Warrant Shares are registered securities. The pre-funded warrants were classified as a component of permanent stockholders’ equity within additional paid-in-capital and were recorded at the issuance date using a relative fair value allocation method. The pre-funded warrants are equity classified because they are freestanding financial instruments that are legally detachable and separately exercisable from the equity instruments, are immediately exercisable, do not embody an obligation for the Company to repurchase its shares, permit the holders to receive a fixed number of common shares upon exercise, are indexed to the Company’s common stock and meet the equity classification criteria. In addition, such pre-funded warrants do not provide any guarantee of value or return. The Company valued the pre-funded warrants at issuance, concluding their sales price approximated their fair value, and allocated net proceeds from the sale proportionately to the common stock and pre-funded warrants of which $37.5 million was allocated to the pre-funded warrants and recorded as a component of additional paid-in-capital. Common Stock Warrants As of June 30, 2020 and December 31, 2019 the following warrants to purchase shares of the Company’s common stock were issued and outstanding: Issue date Expiration date Exercise Price per Share Number of warrants outstanding September 10, 2010 September 10, 2020 $ 30.000 15,296 December 16, 2019 None $ 0.001 2,424,242 2,439,538 There were no warrants exercised during the three and six months ended June 30, 2020 or 2019.

Stock Plans and Stock-Based Com

Stock Plans and Stock-Based Compensation	6 Months Ended
	Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Plans and Stock-Based Compensation	Note 7 – Stock Plans and Stock-Based Compensation Equity Incentive Plans In May 2018, the Company’s stockholders approved (1) the Assembly Biosciences, Inc. 2018 Stock Incentive Plan (the 2018 Plan) pursuant to which the Company reserved 1,900,000 shares of its common stock for issuance in connection with equity incentive awards and (2) the Assembly Biosciences Inc. Employee Stock Purchase Plan (the 2018 ESPP) pursuant to which the Company reserved 400,000 shares of its common stock for issuance in connection with purchases by employees pursuant to this plan. In May 2019, the Company’s stockholders approved an amendment to the 2018 Plan that increased the aggregate number of shares of common stock reserved under the 2018 Plan to In June 2020, the Company’s stockholders approved an amendment to the 2018 Plan that increased the aggregate number of shares of common stock reserved under the 2018 Plan to 4,600,000. As of June 30, 2020, the Company had awards outstanding under the following shareholder-approved plans: 2010 Equity Incentive Plan (the 2010 Plan), which has been frozen; the Amended and Restated 2014 Stock Incentive Plan (the 2014 Plan); and the 2018 Plan. The Company issues new shares of common stock to settle options exercised and vested RSUs. The Company also issues new shares of common stock in connection with purchases of shares of common stock by eligible employees under the Company’s 2018 ESPP. Stock Plan Activity Stock Options A summary of the Company’s option activity and related information for the six months ended June 30, 2020 is as follows: Number of Shares Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (Years) Total Intrinsic Value (in thousands) Outstanding as of December 31, 2019 5,613,353 $ 15.90 Granted 1,275,180 15.92 Exercised (91,713 ) 7.38 Forfeited (144,744 ) 25.57 Outstanding as of June 30, 2020 6,652,076 $ 15.81 7.3 $ 63,186 Options vested and exercisable as of June 30, 2020 3,440,092 $ 14.22 5.6 $ 39,923 The weighted-average grant-date fair value of options granted was $10.52 and $12.68 during the six months ended June 30, 2020 and 2019, respectively. The total intrinsic value of options exercised during the six months ended June 30, 2020 and 2019 was $1.0 million and $0.7 million, respectively. RSUs A summary of the Company’s RSUs and related information for the six months ended June 30, 2020 is as follows: Number of RSUs Weighted Average Fair Value Per RSU at Grant Price Nonvested as of December 31, 2019 758,718 $ 25.47 Granted 531,164 16.31 Vested (99,224 ) 33.59 Forfeited (54,279 ) 25.90 Nonvested as of June 30, 2020 1,136,379 (1) $ 20.45 (1) Includes 157,500 RSUs that have vested but are subject to deferred settlement, which have a weighted average remaining contractual term of 1.7 years. The total fair value of RSUs vested and settled during the six months ended June 30, 2020 and 2019 was $3.1 million and $2.9 million, respectively. The total intrinsic value of RSUs vested and settled during the six months ended June 30, 2020 and 2019 was $1.6 million and $1.3 million, respectively. As of June 30, 2020, RSUs outstanding include 45,000 RSUs granted in December 2017 and 100,000 RSUs granted in September 2019 to executives of the Company with performance-based conditions vesting conditions. As of June 30, 2020, the performance condition for the 45,000 RSUs granted in December 2017 was deemed probable of being met and was subsequently achieved in July 2020. The Company recognized $0.7 ESPP Employees purchased 42,266 and 36,804 shares of common stock under the 2018 ESPP during the six months ended June 30, 2020 and 2019, respectively. Valuation Assumptions The fair value of the stock options granted or modified during the periods indicated was estimated using the Black-Scholes option pricing model, based on the following assumptions: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Exercise price $14.57 - $20.52 $15.22 - $57.33 $14.45 - $20.52 $15.22 - $57.33 Expected volatility 69.13% - 82.24% 66.2% - 83.0% 66.38% - 82.24% 66.2% - 83.2% Risk-free rate 0.36% - 0.60% 2.17% - 2.47% 0.36% - 1.44% 2.17% - 2.65% Expected term (years) 5.5 - 7.5 5.0 - 9.0 5.5 - 7.5 5.0 - 9.0 Expected dividend yield 0% 0% 0% 0% The fair value of RSUs granted is determined based on the price of the Company’s common stock on the date of grant. The fair value of ESPP purchase rights were not material for any period presented. Stock-Based Compensation Expense The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 3,607 $ 3,116 $ 5,551 $ 5,845 General and administrative 3,527 (1,048 ) (1) 6,507 2,800 Total stock-based compensation expense $ 7,134 $ 2,068 $ 12,058 $ 8,645 (1) As of June 30, 2020, there was $32.2 million of total unrecognized stock-based compensation related to outstanding equity awards which is expected to be recognized over a weighted average remaining amortization period of 1.8 years.

Collaboration Agreement

Collaboration Agreement	6 Months Ended
	Jun. 30, 2020
Collaboration Agreement [Abstract]
Collaboration Agreement	Note 8 - Collaboration Agreement Termination of Allergan Collaboration Agreement In January 2017, the Company entered into the Allergan Collaboration Agreement with Allergan to develop and commercialize select microbiome gastrointestinal disease therapies. Pursuant to the Allergan Collaboration Agreement, the Company granted to Allergan an exclusive worldwide license to certain of its intellectual property, including its intellectual property arising under the Allergan Collaboration Agreement, to develop and commercialize licensed compounds for UC, Crohn’s disease, and two compounds for IBS. Allergan and the Company also agreed to collaborate on research and development activities with respect to the licensed compounds in accordance with a mutually agreed upon research and development plan. Per the terms of the Allergan Collaboration Agreement, Allergan could select backups and additional target indications to add to the licenses granted for additional consideration and also had 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 participated in a Joint Development Committee (JDC) and Joint Patent Committee (JPC). Allergan had the right to terminate the Allergan Collaboration Agreement at any time upon advance written notice. In June 2020, following its acquisition of Allergan, AbbVie, on behalf of Allergan, gave written notice of termination of the Allergan Collaboration Agreement, effective 120 days following the delivery of notice, on October 10, 2020. Upon termination, the licenses granted by the Company and its know-how will revert to the Company. Under the terms of the Allergan Collaboration Agreement, AbbVie is obligated to continue to reimburse the Company for certain research and development costs through October 10, 2020. Upon effectiveness of the termination, such reimbursements will cease. Due to the delivery of the termination notice, the Company determined that there were no further enforceable rights and obligations under the Allergan Collaboration Agreement beyond June 2020 and the remaining $36.0 million of deferred revenue was recognized in the period. History of the Allergan Collaboration Agreement Allergan paid the Company an upfront non-refundable payment of $50.0 million, which was received in 2017. Additionally, the Company is eligible to receive variable consideration in the form of research and development cost reimbursements, up to $631.0 million related to seven development milestones and up to $2.14 billion related to 12 commercial development and sales milestones in connection with the successful development and commercialization of licensed compounds. In addition, the Company was 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 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 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 could have elected 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 had an option to co-promote the licensed programs in the U.S. and China, subject to certain conditions set forth in the Allergan Collaboration Agreement. The Company concluded that Allergan was a customer, and the contract was 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 Allergan Collaboration Agreement: (1) grant of licenses to intellectual property for the four initial indications, inclusive of the related technology know-how (Licenses) and (2) the obligation to perform research development services through POC (Development Services). The Company’s participation on the JDC and JPC were considered to be immaterial in the context of the contract. The Company’s co-promotion option was not considered to be a performance obligation. Allergan’s selection of backups or additional target indications to add to the licenses granted for additional consideration and ability to enter into a contract manufacturing agreement with the Company for compound supply at cost plus an agreed upon margin were not considered to be performance obligations as the Company concluded the options were not offered at a discount that exceeds discounts available to other customers, and therefore were not material rights. The grant of additional licensing rights upon option exercises and contract manufacturing agreements were to be accounted for as separate contracts when or if they occurred. The Company concluded the Licenses each were considered to be functional as they ha d 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 wa s dependent on the Company to execute the Development Services, which it wa s uniquely able to perform, in order for Allergan to benefit from the Licenses. As such, the Company determined that it ha d four performance obligations under the Allergan Collaboration Agreement associated with the grant of the four compound Licenses combined with the performance of the Development Services for each of the four compound indications. The Company determined that the four performance obligations would have been performed over the duration of the contract, which began in February 2017 and ended upon receipt of the termination notice . The Company used a cost-based input method to measure proportional performance and to calculate the corresponding amount of revenue to recognize. The Company believe d this was the best measure of progress because other measures do not reflect how the Company transfers its performance obligation to Allergan. In applying the cost-based input method of revenue recognition, the Company measure d costs incurred relative to budgeted costs to fulfill the four performance obligations. These costs consist ed primarily of third-party contract costs and internal labor costs. Revenue was recognized based on actual costs incurred as a percentage of total budgeted costs as the Company complete d its performance obligations. To allocate transaction price among the four performance obligations, the Company estimated their standalone selling price (SSP) using an income-based valuation approach for the estimated value a licensor of the compounds would receive considering the stage of the compounds’ development. A change in the assumptions used to determine its best estimate of selling price for the four performance obligations would not have had 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 the revenue from contracts with customers guidance was limited to $50.0 million upfront payment. Of this amount, the Company allocated $12.5 million to each of the four performance obligations. Research and development cost reimbursement payments are included in the transaction price in the reporting period that the Company concludes that it is probable that recording revenue in the period will not result in a significant reversal in amounts recognized in future periods. The variable consideration related to the remaining development and commercialization milestone payments has not been included in the transaction price as these were fully constrained at June 30, 2020. As part of the Company’s evaluation of the development and commercialization milestones constraint, the Company determined that the achievement of such milestones is contingent upon success in future clinical trials and regulatory approvals which are not within its control and uncertain at this stage. Any variable consideration related to sales-based milestones (including royalties) would have been recognized when the related sales occur as they were determined to relate predominantly to the license granted to Allergan. The Company re-evaluated the transaction price in each reporting period and as uncertain events were resolved or other changes in circumstances occur. The Company did not incur any significant incremental costs of obtaining the Allergan contract. For the six months ended June 30, 2020 and 2019, the Company recognized $43.5 million and $7.0 million, respectively, in revenue associated with the Allergan Collaboration Agreement. Short-term and long-term deferred revenue contract liabilities related to the Allergan Collaboration Agreement were $6.4 million and $30.6 million at December 31, 2019. There were no deferred revenue contract liabilities as of June 30, 2020 due to the Company recognizing a cumulative catch-up adjustment of the remaining deferred revenue balance during the three months ended June 30, 2020 for the determined completion of the Company’s performance obligations under the Allergan Collaboration Agreement upon receipt of the notice of termination from AbbVie. On the unaudited condensed consolidated balance sheets, contract asset balances of $3.3 million and $3.4 million were recorded as accounts receivable from collaboration as of June 30, 2020 and December 31, 2019, respectively. The following table presents changes in the Company’s contract liabilities (in thousands): Balance at Beginning of Period Additions Deductions Balance at End of Period Six Months Ended June 30, 2020 Contract liabilities: Deferred revenue $ 37,048 $ — $ (37,048 ) $ — Balance at Beginning of Period Additions Deductions Balance at End of Period Six Months Ended June 30, 2019 Contract liabilities: Deferred revenue $ 40,660 $ — $ (996 ) $ 39,664 Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Collaboration revenue recognized in the period from Amounts included in deferred revenue at the beginning of the period $ 36,041 $ 137 $ 37,048 $ 996 Performance obligations satisfied in previous period — — — —

Milestones and Research Agreeme

Milestones and Research Agreements	6 Months Ended
	Jun. 30, 2020
Milestones And Research Agreements [Abstract]
Milestones and Research Agreements	Note 9 - Milestones and Research Agreements HBV Research Agreement with Indiana University Since September 2013, the Company has been party to an exclusive License Agreement dated September 3, 2013 with Indiana University Research and Technology Corporation (IURTC) from whom it has licensed aspects of the Company’s HBV program held by IURTC. The license agreement requires the Company to make milestone payments based upon the successful accomplishment of clinical and regulatory milestones. The aggregate amount of all performance milestone payments under the IURTC license agreement, should all milestones through development be met, is $0.8 million, with a portion related to the first performance milestone having been paid. The Company is obligated to pay IURTC royalty payments based on net sales of the licensed technology. The Company is also required to pay diligence maintenance fees each year to the extent that the royalty, sublicensing, and milestone payments to IURTC are less than such fees for that year. Amounts paid in the six months ended June 30, 2020 and 2019 were insignificant. Microbiome Targeted Colonic Delivery Platform In November 2013, the Company entered into a License and Collaboration Agreement with Therabiome, LLC (Therabiome), for all intellectual property and know-how owned or controlled by Therabiome relating to the oral delivery of pharmaceutical drugs to specific sites in the intestine, using a pH sensitive controlled release capsule-in-capsule technology. The Company will be solely responsible for all research and development activities with respect to any product it develops under the license. The Company must pay Therabiome clinical and regulatory milestones for each product or therapy advanced from the platform for U.S. regulatory milestones. In addition, the Company must pay Therabiome lesser amounts for foreign regulatory milestones, which vary by country and region. The Company is also required to pay Therabiome royalties on annual net sales of a product in the low to mid-single digit percentages plus, once annual net sales exceed certain thresholds, a one-time cash payment upon reaching such thresholds. Therabiome must pay the Company royalties on annual net sales of any product Therabiome is permitted to develop using the intellectual property in the low double to mid-double-digit percentages, depending on the level of development or involvement the Company had in the product. No amounts were accrued for this agreement as of and for the six months ended June 30, 2020. Two regulatory milestones were determined to have occurred under this agreement and $0.3 million was accrued and included in accrued expenses during the six months ended June 30, 2019.

Leases

Leases	6 Months Ended
	Jun. 30, 2020
Lease Cost [Abstract]
Leases	Note 10 - Leases Operating Leases The Company leases office space for corporate, administrative and laboratory functions in South San Francisco, California under a sub-sublease that expires in December 2023. The Company also leases office space in Carmel, Indiana under a lease agreement that expires in August 2023, which the Company has subleased. The Company also leases office and laboratory space in Groton, Connecticut under a lease that expires in March 2021. The Company’s China subsidiary leases office space in Shanghai that expires in May 2021 and rents lab space in Shanghai under a lease agreement that expires in December 2020. Additionally, the Company’s China subsidiary leases office space in Beijing under a lease agreement that expires in December 2020. Certain lease contracts contain renewal clauses that the Company assesses on a case by case basis. The Company also leases certain laboratory equipment accounted for as operating leases. Certain equipment leases continue to expire in 2020, with the final lease expiring in 2023. When the Company cannot determine the implicit rate in its leasing arrangements, the Company uses its incremental borrowing rate as the discount rate when measuring operating lease liabilities. The incremental borrowing rate represents an estimate of the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease within a particular currency environment. At June 30, 2020, the Company had operating lease liabilities of $11.1 million and ROU assets of $10.8 million, which were included in the condensed consolidated balance sheet. The following summarizes quantitative information about the Company’s operating leases (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Lease cost Operating lease cost $ 1,158 $ 1,117 $ 2,308 $ 2,208 Short-term lease cost 100 112 200 433 Variable lease cost 408 300 692 599 Total lease cost $ 1,666 $ 1,529 $ 3,200 $ 3,240 Six Months Ended June 30, 2020 2019 Operating cash flows from operating leases $ 2,247 $ 2,099 ROU assets exchanged for new operating lease liabilities $ 545 $ 14,225 As of June 30, 2020 and December 31, 2019, the weighted-average remaining lease term for operating leases was 3.3 years and 2.7 years, respectively. As of June 30, 2020 and December 31, 2019, the weighted-average discount rate for operating leases was 9.5% and 9.4%, respectively. As of June 30, 2020, the maturities of the Company’s operating lease liabilities were as follows (in thousands): Six months ending December 31, 2020 $ 2,356 Year Ending December 31, 2021 3,991 Year Ending December 31, 2022 3,627 Year Ending December 31, 2023 3,325 Total 13,299 Less: present value discount (2,165 ) Operating lease liabilities $ 11,134

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	Note 11 – Subsequent Events On July 17, 2020, the Company entered into a Collaboration Agreement (China Collaboration Agreement) with BeiGene, Ltd. (BeiGene), granting BeiGene an exclusive, royalty-bearing license to develop and commercialize the Company’s novel core inhibitor product candidates ABI-H0731, ABI-H2158 and ABI-H3733 for chronic HBV infection (the Licensed Product Candidates) in the People’s Republic of China, Hong Kong, Taiwan and Macau (the Territory). Pursuant to the terms of the China Collaboration Agreement, the Company received an upfront cash payment of $40.0 million from BeiGene, and the Company is eligible to receive up to approximately $500.0 million in cash milestone payments, comprised of up to $113.8 million for development and regulatory milestones and up to $385.0 million in net sales milestones. In addition, the Company is eligible to receive tiered royalties at percentages ranging from the mid-teens to the low thirties of net sales. BeiGene also agreed to pay all development and regulatory costs for the Licensed Product Candidates in the Territory up to an aggregate of $45.0 million. Development and regulatory costs for the Licensed Product Candidates for the Territory in excess of $45.0 million will be shared equally by the Company and BeiGene. The China Collaboration Agreement also contains provisions such as representations and warranties of the parties, terms as to governance of the collaboration, commercialization and regulatory responsibilities of the parties, and manufacturing and supply, including potential adjustments in the event supply costs exceed certain levels. In addition, during the term of the China Collaboration Agreement, neither party will commercialize any competing products in the Territory. If, after ABI-H2158 and ABI-H3733 reach the end of Phase 2 clinical trials, the Company and BeiGene are unable to mutually agree on the terms of a Phase 3 global study, BeiGene may elect to terminate the China Collaboration Agreement solely as it relates to that compound, as applicable. Such a termination would result in the Company regaining all rights to the applicable compound in the Territory. In addition, BeiGene may terminate the China Collaboration Agreement for convenience at any time upon 90 days’ advance written notice to us. The China Collaboration Agreement also contains customary provisions for termination by either party, including in the event of breach of the China Collaboration Agreement, subject to cure.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and pursuant to the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the U.S. Securities and Exchange Commission (SEC). In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements and include normal recurring adjustments necessary for the fair presentation of the Company’s financial position and its results of operations and comprehensive loss and its cash flows for the periods presented. These statements do not include all disclosures required by U.S. GAAP and should be read in conjunction with the Company’s audited consolidated financial statements and accompanying notes for the fiscal year ended December 31, 2019, which are contained in the Company’s Annual Report on Form 10-K as filed with the SEC on March 4, 2020. The results for the three and six months ended June 30, 2020 are not necessarily indicative of results to be expected for the entire year ending December 31, 2020 or future operating periods.
Use of Estimates	Use of Estimates The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Significant estimates inherent in the preparation of the accompanying unaudited condensed consolidated financial statements include revenue recognition, clinical trial accruals, recoverability and useful lives (indefinite or finite) of intangible assets, assessment of impairment of goodwill, provisions for income taxes, amounts receivable and recognized as revenue under the Allergan Collaboration Agreement, measurement of operating lease liabilities, and the fair value of stock options, stock appreciation rights, and restricted stock units (RSUs) granted to employees, directors and consultants. The Company’s estimates could be affected by external conditions, including those unique to the Company and general economic conditions. It is reasonably possible that these external factors could have an effect on the Company’s estimates and could cause actual results to differ materially from those estimates and assumptions.
Other Risks and Uncertainties	Other Risks and Uncertainties In March 2020, the World Health Organization declared the COVID-19 outbreak a pandemic. To date, the Company’s operations have not been significantly impacted by the COVID-19 pandemic. However, the Company cannot at this time predict the specific extent, duration, or full impact the COVID-19 pandemic will have on its business, operations, strategy, prospects and financial condition and results. The impact of the COVID-19 pandemic on the financial performance of the Company will depend on future developments, including the duration and spread of the outbreak and related governmental advisories and restrictions. These developments and the impact of the COVID-19 pandemic on the financial markets and the overall economy are highly uncertain. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be adversely affected.
Income Taxes	Income Taxes In March 2020, the Families First Coronavirus Response Act (FFCR Act) and the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) were each enacted in response to the COVID-19 pandemic. The FFCR Act and the CARES Act contain numerous income tax provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. In June 2020, Assembly Bill 85 (A.B. 85) was signed into California law. A.B. 85 provides for a three-year three-year The FFCR Act, CARES Act and A.B. 85 did not have a material impact on the Company’s condensed consolidated financial statements as of June 30, 2020; however, the Company continues to examine the impacts the FFCR Act, CARES Act and A.B. 85 may have on its business, results of operations, financial condition and liquidity.
Net Income (Loss) per Share	Net Income (Loss) per Share Basic net income (loss) per common share excludes dilution and is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period. Diluted net income (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. In December 2019, the Company sold 6,287,878 shares of common stock as well as pre-funded warrants to purchase up to 2,424,242 shares of common stock (see Note 6). The pre-funded warrants are exercisable for shares of common stock at a price of $0.001 per share. The shares of common stock into which the pre-funded warrants may be exercised are considered outstanding for the purposes of computing earnings per share because the shares may be issued for little or no consideration, are fully vested, and are exercisable after the original issuance date. A reconciliation of the numerators and the denominators of the basic and diluted net income (loss) per common share computations is as follows (in thousands, except per share amounts): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Numerator: Net income (loss) 7,270 (18,503 ) (19,385 ) (45,555 ) Denominator: Shares used in per share calculation - basic 35,307,669 25,740,500 35,229,570 25,690,617 Dilutive effect of securities 1,983,805 - - - Shares used in per share calculation - diluted 37,291,474 25,740,500 35,229,570 25,690,617 Net income (loss) per share: Basic 0.21 (0.72 ) (0.55 ) (1.77 ) Diluted 0.19 (0.72 ) (0.55 ) (1.77 ) Securities excluded from the computation of diluted income (loss) per share because including them would have been antidilutive are as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Warrants to purchase common stock 15,296 15,296 15,296 15,296 Options to purchase common stock 3,521,778 5,203,935 6,652,076 5,203,935 Common stock subject to purchase under our ESPP 8,991 5,976 8,991 5,976 Unvested RSUs 41,762 489,857 978,879 489,857 Total 3,587,827 5,715,064 7,655,242 5,715,064
Recent Accounting Pronouncements	Adoption of Recent Accounting Pronouncements In January 2017, the Financial Accounting Standards Board (FASB) issued ASU 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment Financial Instruments – Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates On January 1, 2020, the Company adopted ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement, On January 1, 2020, the Company adopted ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes Recent Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	A reconciliation of the numerators and the denominators of the basic and diluted net income (loss) per common share computations is as follows (in thousands, except per share amounts): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Numerator: Net income (loss) 7,270 (18,503 ) (19,385 ) (45,555 ) Denominator: Shares used in per share calculation - basic 35,307,669 25,740,500 35,229,570 25,690,617 Dilutive effect of securities 1,983,805 - - - Shares used in per share calculation - diluted 37,291,474 25,740,500 35,229,570 25,690,617 Net income (loss) per share: Basic 0.21 (0.72 ) (0.55 ) (1.77 ) Diluted 0.19 (0.72 ) (0.55 ) (1.77 )
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	Securities excluded from the computation of diluted income (loss) per share because including them would have been antidilutive are as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Warrants to purchase common stock 15,296 15,296 15,296 15,296 Options to purchase common stock 3,521,778 5,203,935 6,652,076 5,203,935 Common stock subject to purchase under our ESPP 8,991 5,976 8,991 5,976 Unvested RSUs 41,762 489,857 978,879 489,857 Total 3,587,827 5,715,064 7,655,242 5,715,064

Investments in Marketable Sec_2

Investments in Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Schedule of Investments in Marketable Securities	Investments in marketable securities consisted of the following (in thousands): June 30, 2020 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Cash equivalents Money market funds $ 94,524 $ — $ — $ 94,524 Total cash equivalents 94,524 — — 94,524 Short-term investments U.S. and foreign corporate debt securities 32,958 161 — 33,119 Asset-backed securities 22,183 72 — 22,255 U.S. treasury securities 36,080 176 — 36,256 U.S. and foreign commercial paper 38,375 — — 38,375 Total short-term investments 129,596 409 — 130,005 Total cash equivalents and investments $ 224,120 $ 409 $ — $ 224,529 December 31, 2019 Amortized Cost Gross Unrealized Gain (1) Gross Unrealized Loss (1) Fair Value Cash equivalents Money market funds $ 33,095 $ — $ — $ 33,095 U.S. and foreign corporate debt securities 5,000 — (1 ) 4,999 U.S. and foreign commercial paper 4,484 — — 4,484 Total cash equivalents 42,579 — (1 ) 42,578 Short-term investments U.S. and foreign corporate debt securities 72,452 38 (4 ) 72,486 Asset-backed securities 34,008 17 — 34,025 U.S. treasury securities 44,692 24 (2 ) 44,714 U.S. and foreign commercial paper 76,086 — — 76,086 Total short-term investments 227,238 79 (6 ) 227,311 Total cash equivalents and investments $ 269,817 $ 79 $ (7 ) $ 269,889 (1) Gross unrealized gain (loss) is pre-tax.
Schedule of Fair Value of Financial Assets	The following tables present the fair value of the Company’s financial assets measured at fair value on a recurring basis (in thousands): June 30, 2020 Level 1 Level 2 Level 3 Fair Value Cash equivalents Money market fund $ 94,524 $ — $ — $ 94,524 Total cash equivalents 94,524 — — 94,524 Short-term investments U.S. and foreign corporate debt securities — 33,119 — 33,119 Asset-backed securities — 22,255 — 22,255 U.S. treasury securities — 36,256 — 36,256 U.S. and foreign commercial paper — 38,375 — 38,375 Total short-term investments — 130,005 — 130,005 Total assets measured at fair value $ 94,524 $ 130,005 $ — $ 224,529 December 31, 2019 Level 1 Level 2 Level 3 Fair Value Cash equivalents Money market fund 33,095 — — 33,095 U.S. and foreign corporate debt securities — 4,999 — 4,999 U.S. and foreign commercial paper — 4,484 — 4,484 Total cash equivalents 33,095 9,483 — 42,578 Short-term investments U.S. and foreign corporate debt securities — 72,486 — 72,486 Asset-backed securities — 34,025 — 34,025 U.S. treasury securities — 44,714 — 44,714 U.S. and foreign commercial paper — 76,086 — 76,086 Total short-term investments — 227,311 — 227,311 Total assets measured at fair value $ 33,095 $ 236,794 $ — $ 269,889

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	6 Months Ended
	Jun. 30, 2020
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consist of the following (in thousands): Useful life June 30, December 31, (Years) 2020 2019 Lab equipment 3 to 5 $ 290 $ 247 Office equipment 7 699 699 Leasehold improvement 1 to 5 2,084 2,084 Total property and equipment 3,073 3,030 Less: Accumulated depreciation and amortization (1,437 ) (1,200 ) Construction in progress N/A 427 — Property and equipment, net $ 2,063 $ 1,830

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2020
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): June 30, December 31, 2020 2019 Accrued expenses: Accrued compensation $ 4,186 $ 5,312 Accrued restructuring charges 1,019 2,094 Accrued professional fees and other 814 880 Total accrued expenses $ 6,019 $ 8,286

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Summary of Warrants to Purchase Shares of Company's Common Stock	As of June 30, 2020 and December 31, 2019 the following warrants to purchase shares of the Company’s common stock were issued and outstanding: Issue date Expiration date Exercise Price per Share Number of warrants outstanding September 10, 2010 September 10, 2020 $ 30.000 15,296 December 16, 2019 None $ 0.001 2,424,242 2,439,538

Stock Plans and Stock-Based C_2

Stock Plans and Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock Options Activity	A summary of the Company’s option activity and related information for the six months ended June 30, 2020 is as follows: Number of Shares Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (Years) Total Intrinsic Value (in thousands) Outstanding as of December 31, 2019 5,613,353 $ 15.90 Granted 1,275,180 15.92 Exercised (91,713 ) 7.38 Forfeited (144,744 ) 25.57 Outstanding as of June 30, 2020 6,652,076 $ 15.81 7.3 $ 63,186 Options vested and exercisable as of June 30, 2020 3,440,092 $ 14.22 5.6 $ 39,923
Schedule of RSU's and Related Information	A summary of the Company’s RSUs and related information for the six months ended June 30, 2020 is as follows: Number of RSUs Weighted Average Fair Value Per RSU at Grant Price Nonvested as of December 31, 2019 758,718 $ 25.47 Granted 531,164 16.31 Vested (99,224 ) 33.59 Forfeited (54,279 ) 25.90 Nonvested as of June 30, 2020 1,136,379 (1) $ 20.45 (1) Includes 157,500 RSUs that have vested but are subject to deferred settlement, which have a weighted average remaining contractual term of 1.7 years.
Assumptions for Weighted Average Fair Value of Options Granted	The fair value of the stock options granted or modified during the periods indicated was estimated using the Black-Scholes option pricing model, based on the following assumptions: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Exercise price $14.57 - $20.52 $15.22 - $57.33 $14.45 - $20.52 $15.22 - $57.33 Expected volatility 69.13% - 82.24% 66.2% - 83.0% 66.38% - 82.24% 66.2% - 83.2% Risk-free rate 0.36% - 0.60% 2.17% - 2.47% 0.36% - 1.44% 2.17% - 2.65% Expected term (years) 5.5 - 7.5 5.0 - 9.0 5.5 - 7.5 5.0 - 9.0 Expected dividend yield 0% 0% 0% 0%
Schedule of Stock-Based Compensation Expense	The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 3,607 $ 3,116 $ 5,551 $ 5,845 General and administrative 3,527 (1,048 ) (1) 6,507 2,800 Total stock-based compensation expense $ 7,134 $ 2,068 $ 12,058 $ 8,645 (1)

Collaboration Agreement (Tables

Collaboration Agreement (Tables)	6 Months Ended
	Jun. 30, 2020
Collaboration Agreement [Abstract]
Schedule of Changes in Contract Liabilities	The following table presents changes in the Company’s contract liabilities (in thousands): Balance at Beginning of Period Additions Deductions Balance at End of Period Six Months Ended June 30, 2020 Contract liabilities: Deferred revenue $ 37,048 $ — $ (37,048 ) $ — Balance at Beginning of Period Additions Deductions Balance at End of Period Six Months Ended June 30, 2019 Contract liabilities: Deferred revenue $ 40,660 $ — $ (996 ) $ 39,664
Schedule of Collaboration Revenue Recognized with the Period	Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Collaboration revenue recognized in the period from Amounts included in deferred revenue at the beginning of the period $ 36,041 $ 137 $ 37,048 $ 996 Performance obligations satisfied in previous period — — — —

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2020
Lease Cost [Abstract]
Schedule of Quantitative Information of Operating Leases	The following summarizes quantitative information about the Company’s operating leases (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Lease cost Operating lease cost $ 1,158 $ 1,117 $ 2,308 $ 2,208 Short-term lease cost 100 112 200 433 Variable lease cost 408 300 692 599 Total lease cost $ 1,666 $ 1,529 $ 3,200 $ 3,240 Six Months Ended June 30, 2020 2019 Operating cash flows from operating leases $ 2,247 $ 2,099 ROU assets exchanged for new operating lease liabilities $ 545 $ 14,225
Schedule of Maturities Operating Lease Liabilities	As of June 30, 2020, the maturities of the Company’s operating lease liabilities were as follows (in thousands): Six months ending December 31, 2020 $ 2,356 Year Ending December 31, 2021 3,991 Year Ending December 31, 2022 3,627 Year Ending December 31, 2023 3,325 Total 13,299 Less: present value discount (2,165 ) Operating lease liabilities $ 11,134

Nature of Business - Additional

Nature of Business - Additional Information (Details)	6 Months Ended
	Jun. 30, 2020segmentproduct
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Operating segments (in segments) | segment	1
FDA approved products (in products) | product	0

Summary of Significant Accoun_4

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Significant Accounting Policies [Line Items]
Antidilutive securities excluded from computation of earnings (loss)			3,587,827	5,715,064	7,655,242	5,715,064
Performance-Based RSUs
Significant Accounting Policies [Line Items]
Antidilutive securities excluded from computation of earnings (loss)					145,000
Public Offering
Significant Accounting Policies [Line Items]
Number of shares sold		6,287,878
Number of pre-funded warrants sold to purchase of common stock		2,424,242
Pre-funded warrants exercisable price per share		$ 0.001
Public Offering | Common Stock
Significant Accounting Policies [Line Items]
Number of shares sold		6,287,878
California Law
Significant Accounting Policies [Line Items]
Use of net operating loss suspension period	3 years
Cap on use of business incentive tax credits period	3 years
Business incentive tax credit	$ 5
California Law | Taxable Year 2020
Significant Accounting Policies [Line Items]
Maximum taxable income to suspends of use of net operating loss	1
Maximum business incentive tax credits to carryovers	5
California Law | Taxable Year 2021
Significant Accounting Policies [Line Items]
Maximum taxable income to suspends of use of net operating loss	1
Maximum business incentive tax credits to carryovers	5
California Law | Taxable Year 2022
Significant Accounting Policies [Line Items]
Maximum taxable income to suspends of use of net operating loss	1
Maximum business incentive tax credits to carryovers	$ 5

Summary of Significant Accoun_5

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss	$ 7,270	$ (18,503)	$ (19,385)	$ (45,555)
Denominator:
Shares used in per share calculation - basic	35,307,669	25,740,500	35,229,570	25,690,617
Dilutive effect of securities	1,983,805
Shares used in per share calculation - diluted	37,291,474	25,740,500	35,229,570	25,690,617
Net income (loss) per share:
Basic	$ 0.21	$ (0.72)	$ (0.55)	$ (1.77)
Diluted	$ 0.19	$ (0.72)	$ (0.55)	$ (1.77)

Summary of Significant Accoun_6

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	3,587,827	5,715,064	7,655,242	5,715,064
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	15,296	15,296	15,296	15,296
Options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	3,521,778	5,203,935	6,652,076	5,203,935
Common stock subject to purchase under ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	8,991	5,976	8,991	5,976
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings (loss)	41,762	489,857	978,879	489,857

Investments in Marketable Sec_3

Investments in Marketable Securities - Schedule of Investments in Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Investments in marketable securities:
Amortized Cost	$ 96,709	$ 46,732
Fair Value	130,005	227,311
Amortized Cost	224,120	269,817
Gross Unrealized Gain	409	79
Gross Unrealized Loss		(7)
Fair Value	224,529	269,889
Cash equivalents
Investments in marketable securities:
Amortized Cost	94,524	42,579
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	(1)
Fair Value	94,524	42,578
Cash equivalents | Money market fund
Investments in marketable securities:
Amortized Cost	94,524	33,095
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	94,524	33,095
Short-term investments
Investments in marketable securities:
Amortized Cost	129,596	227,238
Gross Unrealized Gain	409	79
Gross Unrealized Loss		(6)
Fair Value	130,005	227,311
U.S and foreign corporate debt securities | Cash equivalents
Investments in marketable securities:
Amortized Cost		5,000
Gross Unrealized Gain		0
Gross Unrealized Loss		(1)
Fair Value		4,999
U.S and foreign corporate debt securities | Short-term investments
Investments in marketable securities:
Amortized Cost	32,958	72,452
Gross Unrealized Gain	161	38
Gross Unrealized Loss		(4)
Fair Value	33,119	72,486
Asset-backed securities | Short-term investments
Investments in marketable securities:
Amortized Cost	22,183	34,008
Gross Unrealized Gain	72	17
Gross Unrealized Loss		0
Fair Value	22,255	34,025
U.S. treasury securities | Short-term investments
Investments in marketable securities:
Amortized Cost	36,080	44,692
Gross Unrealized Gain	176	24
Gross Unrealized Loss	0	(2)
Fair Value	36,256	44,714
U.S. and foreign commercial paper | Cash equivalents
Investments in marketable securities:
Amortized Cost		4,484
Gross Unrealized Gain		0
Gross Unrealized Loss		0
Fair Value		4,484
U.S. and foreign commercial paper | Short-term investments
Investments in marketable securities:
Amortized Cost	38,375	76,086
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	$ 38,375	$ 76,086

Investments in Marketable Sec_4

Investments in Marketable Securities - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Investments in marketable securities:
Long-term marketable securities	$ 0
Fair value assets transfers between level 1, level 2 or level 3	$ 0	$ 0
Short Term Investments
Investments in marketable securities:
Available for sale securities maturity term	less than one year

Investments in Marketable Sec_5

Investments in Marketable Securities - Schedule of Fair Value of Financial Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Short-term investments
Short-term investments	$ 130,005	$ 227,311
Recurring
Cash equivalents
Cash equivalents	94,524	42,578
Short-term investments
Short-term investments	130,005	227,311
Total assets measured at fair value	224,529	269,889
Recurring | U.S and foreign corporate debt securities
Cash equivalents
Cash equivalents		4,999
Short-term investments
Short-term investments	33,119	72,486
Recurring | Asset-backed securities
Short-term investments
Short-term investments	22,255	34,025
Recurring | U.S. treasury securities
Short-term investments
Short-term investments	36,256	44,714
Recurring | U.S. and foreign commercial paper
Cash equivalents
Cash equivalents		4,484
Short-term investments
Short-term investments	38,375	76,086
Recurring | Money market fund
Cash equivalents
Cash equivalents	94,524	33,095
Recurring | Level 1
Cash equivalents
Cash equivalents	94,524	33,095
Short-term investments
Short-term investments	0	0
Total assets measured at fair value	94,524	33,095
Recurring | Level 1 | U.S and foreign corporate debt securities
Cash equivalents
Cash equivalents		0
Short-term investments
Short-term investments	0	0
Recurring | Level 1 | Asset-backed securities
Short-term investments
Short-term investments	0	0
Recurring | Level 1 | U.S. treasury securities
Short-term investments
Short-term investments	0	0
Recurring | Level 1 | U.S. and foreign commercial paper
Cash equivalents
Cash equivalents		0
Short-term investments
Short-term investments	0	0
Recurring | Level 1 | Money market fund
Cash equivalents
Cash equivalents	94,524	33,095
Recurring | Level 2
Cash equivalents
Cash equivalents	0	9,483
Short-term investments
Short-term investments	130,005	227,311
Total assets measured at fair value	130,005	236,794
Recurring | Level 2 | U.S and foreign corporate debt securities
Cash equivalents
Cash equivalents		4,999
Short-term investments
Short-term investments	33,119	72,486
Recurring | Level 2 | Asset-backed securities
Short-term investments
Short-term investments	22,255	34,025
Recurring | Level 2 | U.S. treasury securities
Short-term investments
Short-term investments	36,256	44,714
Recurring | Level 2 | U.S. and foreign commercial paper
Cash equivalents
Cash equivalents		4,484
Short-term investments
Short-term investments	38,375	76,086
Recurring | Level 2 | Money market fund
Cash equivalents
Cash equivalents	0	0
Recurring | Level 3
Cash equivalents
Cash equivalents	0	0
Short-term investments
Short-term investments	0	0
Total assets measured at fair value	0	0
Recurring | Level 3 | U.S and foreign corporate debt securities
Cash equivalents
Cash equivalents		0
Short-term investments
Short-term investments	0	0
Recurring | Level 3 | Asset-backed securities
Short-term investments
Short-term investments	0	0
Recurring | Level 3 | U.S. treasury securities
Short-term investments
Short-term investments	0	0
Recurring | Level 3 | U.S. and foreign commercial paper
Cash equivalents
Cash equivalents		0
Short-term investments
Short-term investments	0	0
Recurring | Level 3 | Money market fund
Cash equivalents
Cash equivalents	$ 0	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment
Total property and equipment	$ 3,073	$ 3,030
Less: Accumulated depreciation and amortization	(1,437)	(1,200)
Property and equipment, net	2,063	1,830
Lab equipment
Property, Plant and Equipment
Total property and equipment	$ 290	247
Lab equipment | Minimum
Property, Plant and Equipment
Useful Life (in years)	3 years
Lab equipment | Maximum
Property, Plant and Equipment
Useful Life (in years)	5 years
Office equipment
Property, Plant and Equipment
Total property and equipment	$ 699	699
Useful Life (in years)	7 years
Leasehold improvement
Property, Plant and Equipment
Total property and equipment	$ 2,084	$ 2,084
Leasehold improvement | Minimum
Property, Plant and Equipment
Useful Life (in years)	1 year
Leasehold improvement | Maximum
Property, Plant and Equipment
Useful Life (in years)	5 years
Construction in progress
Property, Plant and Equipment
Total property and equipment	$ 427

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation	$ 0.1	$ 0.1	$ 0.2	$ 0.3

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accrued expenses:
Accrued compensation	$ 4,186	$ 5,312
Accrued restructuring charges	1,019	2,094
Accrued professional fees and other	814	880
Total accrued expenses	$ 6,019	$ 8,286

Accrued Expenses - Additional I

Accrued Expenses - Additional Information (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued restructuring charges	$ 1,019	$ 2,094

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2017
Subsidiary Sale Of Stock [Line Items]
Preferred stock, shares authorized	5,000,000	5,000,000		5,000,000
Common stock, shares authorized	100,000,000	100,000,000		100,000,000
Preferred stock, shares issued	0	0		0
Preferred stock, shares outstanding	0	0		0
Initial public offering value of shares authorized						$ 250
Common stock remains available for sale		$ 21.4		$ 21.4
Warrants exercisable description				under their terms, the outstanding pre-funded warrants to purchase shares of the Company’s common stock generally may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99% following such exercise.
Proceeds from sale of pre-funded warrants	$ 37.5
Number of warrants exercised		0	0	0	0
Maximum
Subsidiary Sale Of Stock [Line Items]
Ownership percentage to exercise warrant	19.99%
At the Market Offerings
Subsidiary Sale Of Stock [Line Items]
Number of shares sold				0
At the Market Offerings | Maximum
Subsidiary Sale Of Stock [Line Items]
Initial public offering value of shares authorized						$ 75
Public Offering
Subsidiary Sale Of Stock [Line Items]
Number of shares sold	6,287,878
Sale of stock, price per share	$ 16.50
Number of pre-funded warrants sold to purchase of common stock	2,424,242
Sale of stock, price per warrant	$ 16.499
Net proceeds from the issuance of common stock through equity plans	$ 134.7
Pre-funded warrants exercisable price per share	$ 0.001
Underwriters
Subsidiary Sale Of Stock [Line Items]
Number of shares sold	1,136,363

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Warrants to Purchase Shares of Company's Common Stock (Details) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Subsidiary Sale Of Stock [Line Items]
Number of warrants outstanding	2,439,538	2,439,538
Warrants Issued on September 10, 2010
Subsidiary Sale Of Stock [Line Items]
Issue date	Sep. 10, 2010	Sep. 10, 2010
Expiration date	Sep. 10, 2020	Sep. 10, 2020
Exercise Price per Share	$ 30	$ 30
Number of warrants outstanding	15,296	15,296
Warrants Issued on December 16, 2019
Subsidiary Sale Of Stock [Line Items]
Issue date	Dec. 16, 2019	Dec. 16, 2019
Exercise Price per Share	$ 0.001	$ 0.001
Number of warrants outstanding	2,424,242	2,424,242

Stock Plans and Stock-Based C_3

Stock Plans and Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended	6 Months Ended
	Sep. 30, 2019	Dec. 31, 2017	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	May 31, 2019	May 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Shares reserved for issuance (in shares)			4,600,000	4,600,000		3,000,000	1,900,000
Weighted-average grant-date fair value of options granted				$ 10.52	$ 12.68
Total intrinsic value of options exercised				$ 1,000,000	$ 700,000
Stock-based compensation				12,058,000	8,645,000
Unrecognized stock-based compensation expense			$ 32,200,000	$ 32,200,000
Unrecognized stock-based compensation expense expected to be recognized, term				1 year 9 months 18 days
RSUs
Share-based Compensation Arrangement by Share-based Payment Award
Total fair value of awards vested and settled				$ 3,100,000	2,900,000
Total intrinsic value of awards vested and settled				$ 1,600,000	$ 1,300,000
Granted				531,164
RSUs | Executives
Share-based Compensation Arrangement by Share-based Payment Award
Granted	100,000	45,000		100,000
Total fair value of awards				$ 1,200,000
Cumulative catch-up adjustment of stock-based compensation expense			$ 700,000	700,000
Stock-based compensation				$ 0
2018 ESPP
Share-based Compensation Arrangement by Share-based Payment Award
Number of common shares reserved for future issuance							400,000
Number of common stock purchased by employees				42,266	36,804

Stock Plans and Stock-Based C_4

Stock Plans and Stock-Based Compensation - Schedule of Stock Options Activity (Details) - Options - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2020
Number of Shares
Options, Outstanding at beginning of period	5,613,353
Option, Granted	1,275,180
Option, Exercised	(91,713)
Option, Forfeited	(144,744)
Option, Outstanding at end of period	6,652,076
Options vested and exercisable	3,440,092
Weighted Average Exercise Price Per Share
Options, Outstanding at beginning of period	$ 15.90
Option, Granted	15.92
Option, Exercised	7.38
Option, Forfeited	25.57
Option, Outstanding at end of period	15.81
Options vested and exercisable	$ 14.22
Options Outstanding, Weighted Average Remaining Contractual Term (Years)	7 years 3 months 18 days
Options Exercisable, Weighted Average Remaining Contractual Term (Years)	5 years 7 months 6 days
Total Intrinsic Value
Option, Outstanding at end of period	$ 63,186
Options vested and exercisable	$ 39,923

Stock Plans and Stock-Based C_5

Stock Plans and Stock-Based Compensation - Schedule of RSU's and Related Information (Details) - RSUs	6 Months Ended
	Jun. 30, 2020$ / sharesshares
Number of Shares
Beginning of period | shares	758,718
Granted | shares	531,164
Vested | shares	(99,224)
Forfeited | shares	(54,279)
Ending of period | shares	1,136,379
Weighted Average Fair Value Per RSU at Grant Price
Beginning of period | $ / shares	$ 25.47
Granted | $ / shares	16.31
Vested | $ / shares	33.59
Forfeited | $ / shares	25.90
Ending of period | $ / shares	$ 20.45

Stock Plans and Stock-Based C_6

Stock Plans and Stock-Based Compensation - Schedule of RSU's and Related Information (Parenthetical) (Details) - RSUs	6 Months Ended
	Jun. 30, 2020shares
Share-based Compensation Arrangement by Share-based Payment Award
Vested and subject to deferred settlement	157,500
Weighted average remaining contractual term subject to deferred settlement	1 year 8 months 12 days

Stock Plans and Stock-Based C_7

Stock Plans and Stock-Based Compensation - Assumptions for Weighted Average Fair Value of Options Granted (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price	$ 14.57	$ 15.22	$ 14.45	$ 15.22
Expected volatility	69.13%	66.20%	66.38%	66.20%
Risk-free rate	0.36%	2.17%	0.36%	2.17%
Expected term (years)	5 years 6 months	5 years	5 years 6 months	5 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price	$ 20.52	$ 57.33	$ 20.52	$ 57.33
Expected volatility	82.24%	83.00%	82.24%	83.20%
Risk-free rate	0.60%	2.47%	1.44%	2.65%
Expected term (years)	7 years 6 months	9 years	7 years 6 months	9 years

Stock Plans and Stock-Based C_8

Stock Plans and Stock-Based Compensation -Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Compensation expense:
Total stock-based compensation expense	$ 7,134	$ 2,068	$ 12,058	$ 8,645
Research and development
Compensation expense:
Total stock-based compensation expense	3,607	3,116	5,551	5,845
General and administrative
Compensation expense:
Total stock-based compensation expense	$ 3,527	$ (1,048)	$ 6,507	$ 2,800

Stock Plans and Stock-Based C_9

Stock Plans and Stock-Based Compensation -Schedule of Stock-Based Compensation Expense (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Compensation expense:
Total stock-based compensation expense	$ 7,134	$ 2,068	$ 12,058	$ 8,645
Former Officer
Compensation expense:
Total stock-based compensation expense		$ (3,600)

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Details)	Feb. 10, 2017USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)Milestone	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Collaboration Agreements:
Deferred revenue recognized		$ 36,041,000	$ 137,000	$ 37,048,000	$ 996,000
Non-refundable upfront payment received		0	39,664,000	0	39,664,000	$ 37,048,000	$ 40,660,000
Collaboration revenue		39,376,000	$ 3,080,000	43,457,000	6,966,000
Contract with customer, liability, current						6,411,000
Contract with customer, liability, noncurrent						30,637,000
Accounts receivable from collaboration		3,315,000		3,315,000		3,374,000
Allergan
Collaboration Agreements:
Agreed to share maximum amount development cost	$ 75,000,000
Premium percentage on agreed contribution development cost amount	25.00%
Allergan Collaboration Agreement
Collaboration Agreements:
Deferred revenue recognized		36,000,000
Non-refundable upfront payment received	$ 50,000,000	$ 0		0
Collaboration revenue on each performance obligation	$ 12,500,000
Collaboration revenue				43,500,000	$ 7,000,000
Contract with customer, liability, current						6,400,000
Contract with customer, liability, noncurrent						$ 30,600,000
Allergan Collaboration Agreement | Milestone Scenario One
Collaboration Agreements:
Potential milestone payments				$ 631,000,000
Number of milestones | Milestone				7
Allergan Collaboration Agreement | Milestone Scenario Two
Collaboration Agreements:
Potential milestone payments				$ 2,140,000,000
Number of milestones | Milestone				12

Collaboration Agreement - Sched

Collaboration Agreement - Schedule of Changes in Contract Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Collaboration Agreement [Abstract]
Balance at Beginning of Period	$ 37,048	$ 40,660
Additions	0	0
Deductions	(37,048)	(996)
Balance at End of Period	$ 0	$ 39,664

Collaboration Agreement - Sch_2

Collaboration Agreement - Schedule of Collaboration Revenue Recognized with the Period (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Collaboration revenue recognized in the period from
Amounts included in deferred revenue at the beginning of the period	$ 36,041	$ 137	$ 37,048	$ 996
Performance obligations satisfied in previous period	$ 0	$ 0	$ 0	$ 0

Milestones and Research Agree_2

Milestones and Research Agreements - Additional Information (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Milestone and Research Agreements:
Potential milestone payment	$ 800
Accrued expenses	6,019	$ 8,286
License Agreement Terms
Milestone and Research Agreements:
Accrued expenses	$ 0		$ 300

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease, liability	$ 11,134
Operating lease, ROU assets	$ 10,780	$ 11,975
Weighted-average remaining lease term - operating leases	3 years 3 months 18 days	2 years 8 months 12 days
Weighted-average discount rate - operating leases	9.50%	9.40%

Leases - Schedule of Quantitati

Leases - Schedule of Quantitative Information of Operating Leases (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lease cost
Operating lease cost	$ 1,158	$ 1,117	$ 2,308	$ 2,208
Short-term lease cost	100	112	200	433
Variable lease cost	408	300	692	599
Total lease cost	$ 1,666	$ 1,529	3,200	3,240
Operating cash flows from operating leases			2,247	2,099
Operating lease liabilities arising from obtaining ROU assets			$ 545	$ 14,225

Leases - Schedule of Maturities

Leases - Schedule of Maturities Operating Lease Liabilities (Details) $ in Thousands	Jun. 30, 2020USD ($)
Lease Cost [Abstract]
Six months ending December 31, 2020	$ 2,356
Year Ending December 31, 2021	3,991
Year Ending December 31, 2022	3,627
Year Ending December 31, 2023	3,325
Total	13,299
Less: present value discount	(2,165)
Operating lease liabilities	$ 11,134

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - China Collaboration Agreement - Subsequent Event - BeiGene, Ltd. $ in Millions	Jul. 17, 2020USD ($)
Subsequent Event [Line Items]
Upfront cash payment received	$ 40
Agreed to pay maximum amount development and regulatory costs	45
Maximum
Subsequent Event [Line Items]
Potential milestone payments	500
Development and Regulatory | Maximum
Subsequent Event [Line Items]
Potential milestone payments	113.8
Sales Milestone Payments | Maximum
Subsequent Event [Line Items]
Potential milestone payments	$ 385