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Document And Entity Information - USD ($) $ in Millions	12 Months Ended
Document And Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Mar. 18, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	GOSSAMER BIO, INC.
Trading Symbol	GOSS
Entity Central Index Key	0001728117
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Public Float			$ 947.8
Entity Common Stock, Shares Outstanding		66,336,562
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity File Number	001-38796
Entity Tax Identification Number	47-5461709
Entity Address, Address Line One	3013 Science Park Road
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Incorporation, State or Country Code	DE
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	684-1300
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	Certain sections of the registrant’s definitive proxy statement for the 2020 annual meeting of stockholders to be filed with the Securities and Exchange Commission pursuant to Regulation 14A not later than 120 days after end of this fiscal year covered by this Form 10-K are incorporated by reference into Part III of this Form 10-K.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 135,089	$ 105,219
Marketable securities	266,740	123,439
Restricted cash	0	200
Prepaid expenses and other current assets	7,488	3,095
Total current assets	409,317	231,953
Property and equipment, net	5,425	3,193
Operating lease right-of-use assets	10,303
Other assets	1,559	4,273
Total assets	426,604	239,419
Current liabilities
Accounts payable	956	2,182
Accrued research and development expenses	19,258	10,653
Accrued expenses and other current liabilities	16,709	7,568
Total current liabilities	36,923	20,403
Long-term debt	28,459
Operating lease liabilities - long-term	8,737
Accrued expenses - long-term		718
Total liabilities	74,119	21,121
Commitments and contingencies
Stockholders' equity (deficit)
Common stock, $0.0001 par value; 700,000,000 shares authorized as of December 31, 2019 and 49,160,177 shares authorized as of December 31, 2018; 66,284,003 shares issued and 61,635,477 shares outstanding as of December 31, 2019, and 15,533,450 shares issued and 8,051,418 shares outstanding as of December 31, 2018	7	2
Additional paid-in capital	686,390	33,853
Accumulated deficit	(334,170)	(153,863)
Accumulated other comprehensive income (loss)	258	(61)
Total stockholders' equity (deficit)	352,485	(120,069)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 426,604	239,419
Series Seed Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference		29,200
Series A Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference		79,615
Series B Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference		$ 229,552

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	700,000,000	49,160,177
Common stock, shares, issued	66,284,003	15,533,450
Common stock, shares, outstanding	61,635,477	8,051,418
Series Seed Convertible Preferred Stock
Temporary equity, par value	$ 0.0001	$ 0.0001
Temporary equity, shares issued	0	20,000,000
Temporary equity, shares outstanding	0	20,000,000
Temporary equity, liquidation preference	$ 0	$ 20,000
Series A Convertible Preferred Stock
Temporary equity, par value	$ 0.0001	$ 0.0001
Temporary equity, shares issued	0	45,714,286
Temporary equity, shares outstanding	0	45,714,286
Temporary equity, liquidation preference	$ 0	$ 80,000
Series B Convertible Preferred Stock
Temporary equity, par value	$ 0.0001	$ 0.0001
Temporary equity, shares issued	0	71,506,513
Temporary equity, shares outstanding	0	71,506,513
Temporary equity, liquidation preference	$ 0	$ 230,000

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 143,403	$ 55,283	$ 891
In process research and development	3,600	49,659	5,500
General and administrative	39,136	44,051	262
Total operating expenses	186,139	148,993	6,653
Loss from operations	(186,139)	(148,993)	(6,653)
Other income (expense), net	5,832	2,024	(118)
Net loss	(180,307)	(146,969)	(6,771)
Other comprehensive income:
Foreign currency translation, net of tax	(12)
Unrealized gain (loss) on marketable securities, net of tax	331	(61)
Other comprehensive income (loss)	319	(61)
Comprehensive loss	$ (179,988)	$ (147,030)	$ (6,771)
Net loss per share, basic and diluted	$ (3.29)	$ (22.59)	$ (0.74)
Weighted average common shares outstanding, basic and diluted	54,740,170	6,504,871	9,160,888

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in-Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Series Seed Convertible Preferred Stock	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock
Beginning balance at Dec. 31, 2016	$ (123)			$ (123)
Beginning balance, shares at Dec. 31, 2016		9,160,888
Stock-based compensation	32		$ 32
Net loss	(6,771)			(6,771)
Ending balance at Dec. 31, 2017	(6,862)		32	(6,894)
Ending balance, shares at Dec. 31, 2017		9,160,888
Issuance of Series A preferred stock for cash, net of $0.4 million in offering costs							$ 73,491
Issuance of Series A preferred stock for cash, net of $0.4 million in offering costs, shares							42,215,077
Issuance of stock for acquisition	2,875	$ 1	2,874
Temporary equity, issuance of stock for acquisition, shares						20,000,000
Temporary equity, issuance of stock for acquisition						$ 29,200
Issuance of stock for acquisition. shares		1,101,278
Issuance of Series A preferred stock to convert debt and accrued interest, shares							3,499,209
Issuance of Series A preferred stock to convert debt and accrued interest							$ 6,124
Issuance of Series B preferred stock for cash, net of $0.5 million in offering costs								$ 229,552
Issuance of Series B preferred stock for cash, net of $0.5 in offering costs, shares								71,506,513
Vesting of restricted stock	1	$ 1
Vesting of restricted stock, shares		2,369,696
Incremental vesting conditions placed on previously issued common shares		4,580,444
Stock-based compensation	30,947		30,947
Net loss	(146,969)			(146,969)
Other comprehensive income (loss)	(61)				$ (61)
Ending balance at Dec. 31, 2018	(120,069)	$ 2	33,853	(153,863)	(61)
Temporary equity, ending balance, shares at Dec. 31, 2018						20,000,000	45,714,286	71,506,513
Temporary equity, ending balance at Dec. 31, 2018						$ 29,200	$ 79,615	$ 229,552
Ending balance, shares at Dec. 31, 2018		8,051,418
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs	291,311	$ 2	291,309
Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs, shares		19,837,500
Convertible preferred stock, conversion of convertible preferred stock into common stock, shares						(20,000,000)	(45,714,286)	(71,506,513)
Convertible preferred stock, conversion of convertible preferred stock into common stock						$ (29,200)	$ (79,615)	$ (229,552)
Conversion of convertible preferred stock into common stock, shares		30,493,460
Conversion of convertible preferred stock into common stock	338,367	$ 3	338,364
Vesting of restricted stock, shares		2,833,506
Exercise of stock options	$ 2,045		2,045
Exercise of stock options, shares	419,593	419,593
Stock-based compensation	$ 20,819		20,819
Net loss	(180,307)			(180,307)
Other comprehensive income (loss)	319				319
Ending balance at Dec. 31, 2019	$ 352,485	$ 7	$ 686,390	$ (334,170)	$ 258
Temporary equity, ending balance, shares at Dec. 31, 2019						0	0	0
Ending balance, shares at Dec. 31, 2019		61,635,477

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Series A Convertible Preferred Stock
Issuance of shares, offering costs	$ 0.4
Series B Convertible Preferred Stock
Issuance of shares, offering costs	$ 0.5

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net loss	$ (180,307)	$ (146,969)	$ (6,771)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	917	297
Stock-based compensation expense	20,819	30,947	32
In process research and development expenses	3,600	49,659
Amortization of operating lease right-of-use assets	2,172
Amortization of long-term debt discount and issuance costs	237
Amortization of premium on investments, net of accretion of discounts	(2,364)
Net realized gain on investments	(28)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(4,393)	(2,827)	(130)
Other assets	2,714	(584)
Operating lease liabilities	(2,108)
Accounts payable	(1,399)	2,085	57
Accrued expenses	1,521	5,938	824
Accrued research and development expenses	8,605	10,527	126
Accrued compensation and benefits	5,180
Accrued interest expense		(117)	117
Net cash used in operating activities	(144,834)	(51,044)	(5,745)
Cash flows from investing activities
Research and development asset acquisitions, net of cash acquired	(3,600)	(17,721)
Purchase of marketable securities	(499,079)	(123,500)
Maturities of marketable securities	328,000
Sales of marketable securities	30,501
Purchase of property and equipment	(2,966)	(3,490)
Net cash used in investing activities	(147,144)	(144,711)
Cash flows from financing activities
Proceeds from issuance of convertible note			6,000
Proceeds from issuance of common stock in a public offering, net	291,311
Proceeds from the issuance of long-term debt, net of debt discount and issuance costs of $1,778	28,222
Proceeds from the exercise of stock options	2,045
Repayment of notes payable to related parties		(40)
Payment of deferred offering costs		(2,144)
Net cash provided by financing activities	321,578	300,859	6,000
Effect of exchange rate changes on cash, cash equivalents and restricted cash	70
Net increase in cash, cash equivalents and restricted cash	29,600	105,104	255
Cash, cash equivalents and restricted cash, at the beginning of the period	105,419	315	60
Cash, cash equivalents and restricted cash, at the end of the period	135,089	105,419	$ 315
Supplemental disclosure of cash flow information:
Cash paid for interest	1,475	119
Supplemental disclosure of noncash investing and financing activities:
Acquisition of in-process research and development through issuance of stock		19,284
Issuance of Series A convertible preferred stock to convert debt and accrued interest		6,124
Unpaid deferred offering costs - net		1,545
Right-of-use assets obtained in exchange for lease liabilities	12,458
Conversion of convertible preferred stock to common stock	338,367
Change in unrealized gain on marketable securities, net of tax	331	(61)
Unpaid property and equipment	$ 183
Series A Convertible Preferred Stock
Cash flows from financing activities
Proceeds from issuance of convertible preferred stock, net		73,491
Series B Convertible Preferred Stock
Cash flows from financing activities
Proceeds from issuance of convertible preferred stock, net		$ 229,552

Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Statement Of Cash Flows [Abstract]
Debt issuance costs	$ 1,778

Organization and Basis of Presentation

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Organization and Basis of Presentation

Note 1—Organization and Basis of Presentation

Gossamer Bio, Inc. (including its subsidiaries, the “Company”) is a clinical-stage biopharmaceutical company focused on discovering, acquiring, developing and commercializing therapeutics in the disease areas of immunology, inflammation and oncology. The Company was incorporated in the state of Delaware on October 25, 2015 (originally as FSG Bio, Inc.) and is based in San Diego, California.

The consolidated financial statements include the accounts of Gossamer Bio, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions among the consolidated entity have been eliminated in consolidation.

Initial Public Offering in February 2019

On February 12, 2019, the Company completed its initial public offering (“IPO”) with the sale of 19,837,500 shares of common stock, including shares of common stock issued upon the exercise in full of the underwriters’ option to purchase additional shares, at a public offering price of $16.00 per share, resulting in net proceeds of $291.3 million, after deducting underwriting discounts, commissions, and offering expenses.

Liquidity and Capital Resources

The Company has incurred significant operating losses since its inception. As of December 31, 2019 and 2018, the Company had an accumulated deficit of $334.2 million and $153.9 million, respectively.

From the Company’s inception through the year ended December 31, 2019, the Company has funded its operations primarily through equity financings. The Company raised $601.3 million from October 2017 through February 2019 through Series A and Series B Convertible Preferred Stock, convertible note financings, and the completed IPO, after deducting underwriting discounts, commissions, and offering expenses. In addition, the Company received $12.8 million in cash in connection with the January 2018 acquisition of AA Biopharma Inc. On May 2, 2019 the Company as guarantor, and its wholly-owned subsidiary GB001, as borrower, entered into a credit, guaranty and security agreement, as amended on September 18, 2019 (the “Credit Facility), with MidCap Financial Trust (“MidCap”), an agent and as lender, and the additional lenders party thereto from time to time (together with MidCap, the “Lenders”), pursuant to which the Lenders, including affiliates of MidCap and Silicon Valley Bank, agreed to make term loans available to the Company for working capital and general business purposes, in a principal amount of up to $150.0 million in term loan commitments, including a $30.0 million term loan that was funded at the closing date. Under the Credit Facility, the Company has the ability to access the remaining $120.0 million in three additional tranches (of $40.0 million, $30.0 million and $50.0 million, respectively), subject to specified availability periods, the achievement of certain clinical development milestones, minimum cash requirements and other customary conditions. As of December 31, 2019, no other tranches under the Credit Facility have been drawn. See Note 5 for additional information regarding the Credit Facility.

The Company expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As a result, the Company will need to raise capital through equity offerings, debt financings and other capital sources, including potential collaborations, licenses and other similar arrangements. Management believes that it has sufficient working capital on hand to fund operations through at least the next twelve months from the date these consolidated financial statements were available to be issued. There can be no assurance that the Company will be successful in acquiring additional funding, that the Company’s projections of its future working capital needs will prove accurate, or that any additional funding would be sufficient to continue operations in future years.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2—Summary of Significant Accounting Policies

Basis of Presentation

The Company’s consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Certain prior period amounts have been reclassified to conform to the current period presentation.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. The most significant estimates in the Company’s consolidated financial statements relate to accrued research and development expenses, the valuation of stock options and the valuation allowance of deferred tax assets resulting from net operating losses. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results could differ from those estimates.

Segments

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.

Cash and Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less to be cash equivalents. The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents are valued at cost, which approximate their fair value.

Marketable Securities

The Company considers securities with original maturities of greater than 90 days to be marketable securities. The Company has the ability, if necessary, to liquidate any of its cash equivalents and marketable securities to meet its liquidity needs in the next 12 months. Accordingly, those investments with contractual maturities greater than one year from the date of purchase are classified as current assets on the accompanying condensed consolidated balance sheets. The Company’s marketable securities consist of U.S. Treasury and agency securities, commercial paper, and corporate debt securities. Marketable securities are recorded at fair value and unrealized gains and losses are recorded within accumulated other comprehensive loss. The estimated fair value of the marketable securities is determined based on quoted market prices or rates for similar instruments. The Company evaluates securities with unrealized losses to determine whether such losses, if any, are other than temporary. Realized gains and losses are calculated using the specific identification method and recorded as interest income or expense. The Company does not generally intend to sell the investments and it is not more likely than not that it will be required to sell the investments before recovery of their amortized cost bases, which may be at maturity. The Company has determined that there were no other than temporary declines in fair values of its investments as of December 31, 2019.

Restricted Cash

The Company had no restricted cash as of December 31, 2019. Restricted cash as of December 31, 2018 served as collateral for the Company’s corporate credit card program.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash, cash equivalents and marketable securities are financial instruments that are potentially subject to concentrations of credit risk. The Company’s cash and cash equivalents are deposited in accounts at large financial institutions, and amounts may exceed federally insured limits. The Company believes it is not exposed to significant credit risk due to the financial strength of the depository institutions in which the cash and cash equivalents are held. The Company maintains its cash equivalents in U.S. Treasury and agency securities and commercial paper with maturities less than three months and in money market funds that invest in U.S. Treasury and agency securities.

The Company’s available for sale securities are also invested in U.S. Treasury and agency securities. The Company has not recognized any losses from credit risks on such accounts during any of the periods presented. The Company believes it is not exposed to significant credit risk on its cash, cash equivalents and available for sale securities.

Property and Equipment, Net

Property and equipment, net, which consists mainly of office equipment and leasehold improvements, are carried at cost less accumulated depreciation. Depreciation is computed over the estimated useful lives of the respective assets, generally three to seven years, using the straight-line method.

Deferred Offering Costs

The Company capitalizes certain legal and other third-party fees that are directly associated with in process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded as a reduction of the proceeds generated as a result of the offering. There were no deferred offering costs as of December 31, 2019. Deferred offering costs amounted to $2.1 million as of December 31, 2018 and was recorded as a component of other assets on the consolidated balance sheets.

Leases

In accordance with Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842), as adopted on January 1, 2019, the Company determines if an arrangement is a lease at inception. Operating leases are included in the balance sheet as right-of-use assets and operating lease liabilities at the present value of the lease payments calculated using the Company’s incremental borrowing rate, unless the implicit rate is readily available. The Company records rent expense on a straight-line basis over the term of the lease.

Research and Development

All research and development costs are expensed as incurred. Research and development costs consist primarily of salaries, employee benefits, costs associated with preclinical studies and clinical trials (including amounts paid to clinical research organizations and other professional services), in process research and development expenses and license agreement expenses. Payments made prior to the receipt of goods or services to be used in research and development are capitalized until the goods or services are received.

The Company records accruals for estimated research and development costs, comprising payments for work performed by third party contractors, laboratories, participating clinical trial sites, and others. Some of these contractor’s bill monthly based on actual services performed, while others bill periodically based upon achieving certain contractual milestones. For the latter, the Company accrues the expenses as goods or services are used or rendered. Clinical trial site costs related to patient enrollment are accrued as patients enter and progress through the trial. Upfront costs, such as costs associated with setting up clinical trial sites for participation in the trials, are expensed immediately once incurred as research and development expenses.

Patent Costs

Costs related to filing and pursuing patent applications are expensed as incurred, as recoverability of such expenditures is uncertain. These costs are included in general and administrative expenses.

Income Taxes

Income taxes are recorded in accordance with Financial Accounting Standards Board (“FASB”) Standards Codification (“ASC”) No. 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit would more likely than not be realized assuming examination by the taxing authority. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances.

Deferred tax assets and liabilities reflect the future tax consequences of the differences between the financial reporting and tax bases of assets and liabilities using current enacted tax rates. Valuation allowances are recorded when the realizability of such deferred tax assets does not meet a more-likely-than-not threshold. For tax benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. The Company is subject to taxation in the United States and California, Ireland and Luxembourg. As of December 31, 2019, the Company’s tax years since inception are subject to examination by taxing authorities due to the Company’s unutilized NOLs and tax credits.

Stock-Based Compensation

The Company expenses stock-based compensation to employees and non-employees over the requisite service period based on the estimated grant-date fair value of the awards. The Company records the expense for stock-based compensation awards subject to performance-based milestone vesting over the remaining service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the expected satisfaction of the performance conditions at each reporting date. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, and the assumptions used in calculating the fair value of stock-based awards represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment. The Company accounts for forfeitures as they occur. All share-based compensation costs are recorded in the statements of operations based upon the underlying employees or non-employee’s roles within the Company.

Foreign Currency

Assets and liabilities of non-U.S. subsidiaries that operate in a local currency environment, where that local currency is the functional currency, are translated to U.S. dollars at exchange rates in effect at the balance sheet date. Income and expense accounts are translated at average exchange rates during the year which approximate the rates in effect at the transaction dates. The resulting translation adjustments are recorded in accumulated other comprehensive income (loss). Foreign exchange transaction gains and losses are included in other income (expense) in the Company’s consolidated statement of operations and comprehensive loss.

Recent Accounting Pronouncements—To Be Adopted

In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which changes the impairment model for most financial assets and certain other instruments. For trade receivables and other instruments, entities will be required to use a new forward-looking expected loss model that generally will result in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses will be recognized as allowances rather than as reductions in the amortized cost of the securities. This guidance is effective for annual reporting periods beginning after December 15, 2019, including interim periods within those years, with early adoption permitted only as of annual reporting periods beginning after December 15, 2018. The Company has evaluated ASU 2016-13 and determined that the adoption of the new standard will not have a material impact on the Company's consolidated financial statements or related financial statement disclosures.

Recently Adopted Accounting Pronouncements

The Company adopted ASU No. 2016-02, Leases (Topic 842) (“ASC 842”), as of January 1, 2019, using the optional transition method. The optional transition method provides a method for recording existing leases at adoption and a cumulative catch up adjustment on January 1, 2019 for any differences between ASC 842 and the legacy guidance provided in ASC 840, Leases that would have impacted our income statement. No retrospective restatements are required under the optional transition method. In addition, the Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed us to carry forward the historical lease classification. The Company also applied the short-term lease recognition exemption for leases with terms at inception not greater than 12 months and elected to not separate lease and non-lease components for its long-term leases.

Adoption of the new standard resulted in the recording of additional operating lease right-of-use assets and operating lease liabilities of approximately $12.5 million and $13.2 million, respectively, as of January 1, 2019. The difference between the operating lease right-of-use assets and lease liabilities are due to accrued deferred rent and unamortized lease incentives.

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU simplifies the accounting for income taxes by eliminating certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period, and the recognition of deferred tax liabilities for outside basis differences. It also clarifies and simplifies other aspects of the accounting for income taxes. The guidance is effective for fiscal years beginning after December 15, 2020, with early adoption permitted in any annual or interim period for which financial statements have not yet been issued or made available for issuance. The Company early adopted this standard as of October 1, 2019. The adoption of this ASU did not have a material impact on the Company’s consolidated financial statements or related disclosures.

Net Loss Per Share

Basic net loss per share of common stock is computed by dividing net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss per share excludes the potential impact of Series Seed Convertible Preferred Stock, Series A Convertible Preferred Stock, and Series B Convertible Preferred Stock, common stock options and unvested shares of restricted stock because their effect would be anti-dilutive due to the Company’s net loss. Since the Company had a net loss in each of the periods presented, basic and diluted net loss per common share are the same.

The table below provides potentially dilutive securities not included in the calculation of the diluted net loss per share because to do so would be anti-dilutive:

	December 31,
	2019		2018		2017
Shares issuable upon conversion of Series Seed Convertible Preferred Stock		—		4,444,444		—
Shares issuable upon conversion of Series A Convertible Preferred Stock		—		10,158,710		—
Shares issuable upon conversion of Series B Convertible Preferred Stock		—		15,890,306		—
Shares issuable upon exercise of stock options		8,538,060		5,107,329		—
Non-vested shares under restricted stock grants		4,648,526		7,482,032		1,305,421

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

Note 3—Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	Years Ended December 31,
	2019		2018
Accrued compensation	$	9,282	$	4,102
Operating lease liabilities, current		2,354		—
Accrued in process research and development		1,600		—
Accrued consulting fees		1,337		665
Accrued other		1,126		769
Accrued legal fees		837		1,310
Accrued accounting fees		173		722
Total accrued expenses	$	16,709	$	7,568

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

Note 4—Fair Value Measurements

The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Observable inputs such as quoted prices in active markets;

Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

The Company classifies its cash equivalents and available-for-sale investments within Level 1 or Level 2. The fair value of the Company’s investment grade corporate debt securities and commercial paper is determined using proprietary valuation models and analytical tools, which utilize market pricing or prices for similar instruments that are both objective and publicly available, such as matrix pricing or reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, and offers.

Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table presents the hierarchy for assets measured at fair value on a recurring basis as of December 31, 2019 and December 31, 2018 (in thousands):

	Fair Value Measurements at End of Period Using:
			Quoted Market		Significant		Significant
			Prices for		Other Observable		Unobservable
	Total		Identical Assets		Inputs		Inputs
	Fair Value		(Level 1)		(Level 2)		(Level 3)
As of December 31, 2019
Money market funds	$	82,125	$	82,125	$	—	$	—
U.S. Treasury and agency securities		91,717		91,717		—		—
Commercial paper		37,411		—		37,411		—
Corporate debt securities		156,277		—		156,277		—
As of December 31, 2018
Money market funds	$	17,295	$	17,295	$	—	$	—
U.S. Treasury securities		123,439		123,439		—		—

Fair Value of Other Financial Instruments

As of December 31, 2019 and December 31, 2018, the carrying amounts of the Company’s financial instruments, which include cash, interest and securities receivable, accounts payable and accrued expenses, approximate fair values because of their short maturities.

Interest receivable as of December 31, 2019 and December 31, 2018 was $1.5 million and $0.5 million, respectively, and is recorded as a component of prepaid expenses and other current assets on the condensed consolidated balance sheets. Securities receivable reflect the timing differences of maturities or settlements of investments and the ultimate reinvestment of such amounts.

The Company believes that its Credit Facility bears interest at a rate that approximates prevailing market rates for instruments with similar characteristics and, accordingly, the carrying value of the Credit Facility approximates fair value. The Company estimates the fair value of long-term debt utilizing an income approach. The Company uses a present value calculation to discount principal and interest payments and the final maturity payment on these liabilities using a discounted cash flow model based on observable inputs. The debt instrument is then discounted based on what the current market rates would be as of the reporting date. Based on the assumptions used to value these liabilities at fair value, the debt instrument is categorized as Level 2 in the fair value hierarchy.

Available for Sale Investments

The Company invests its excess cash in U.S. Treasury and agency securities and debt instruments of corporations and commercial obligations, which are classified as available-for-sale investments. These investments are carried at fair value and are included in the tables above. The Company evaluates securities with unrealized losses to determine whether such losses, if any, are other than temporary. Realized gains and losses are calculated using the specific identification method and recorded as interest income or expense. The Company does not generally intend to sell the investments and it is not more likely than not that it will be required to sell the investments before recovery of their amortized cost bases, which may be at maturity.

The aggregate market value, cost basis, and gross unrealized gains and losses of available-for-sale investments by security type, classified in marketable securities and long-term investments as of December 31, 2019 are as follows (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Total
	Cost		Gains		Losses			Fair Value
Marketable securities
U.S. Treasury and agency securities	$	77,993	$	57	$	—		$	78,050
Commercial paper		32,413		—		—			32,413
Corporate debt securities		156,059		238		(20	)		156,277
Total marketable securities	$	266,465	$	295	$	(20	)	$	266,740

As of December 31, 2019, the Company classified $18.7 million of assets with original maturities of 90 days or less as cash equivalents. None of the investments have been in a gross unrealized loss for a period greater than 12 months. At each reporting date, the Company performs an evaluation of impairment to determine if any unrealized losses are other-than-temporary. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition of the issuer, and our intent and ability to hold the investment until recovery of the amortized cost basis. The Company intends and has the ability to hold its investments in unrealized loss positions until their amortized cost basis has been recovered. Further, based on its evaluation, the Company determined that unrealized losses were not other-than-temporary as of December 31, 2019.

Contractual maturities of available-for-sale debt securities, as of December 31, 2019, were as follows (in thousands):

	Estimated
	Fair Value
Due within one year	$	237,449
One to two years		29,291
Total	$	266,740

The Company has the ability, if necessary, to liquidate any of its cash equivalents and marketable securities to meet its liquidity needs in the next 12 months. Accordingly, those investments with contractual maturities greater than one year from the date of purchase are classified as current assets on the accompanying consolidated balance sheets.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Long-Term Debt

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Long-term Debt

Note 5—Long-term Debt

On May 2, 2019, the Company entered into the Credit Facility described in Note 1, pursuant to which the Lenders agreed to make term loans available to the Company for working capital and general business purposes, in a principal amount of up to $150.0 million in term loan commitments, including a $30.0 million term loan that was funded at the closing date, with the ability to access the remaining $120.0 million in three additional tranches (of $40.0 million, $30.0 million and $50.0 million, respectively), subject to specified availability periods, the achievement of certain clinical development milestones, minimum cash requirements and other customary conditions. The second tranche is available no earlier than February 1, 2020 and no later than July 31, 2020. The third tranche is available no earlier than May 1, 2020 and no later than October 31, 2020. The fourth tranche is available no earlier than February 1, 2021 and no later than July 31, 2021. The Credit Facility is secured by substantially all of the Company’s and its domestic subsidiaries’ personal property, including intellectual property, and includes affirmative and negative covenants applicable to the Company.

Each term loan under the Credit Facility bears interest at an annual rate equal to the sum of (i) one-month LIBOR (customarily defined, with a change to prime rate if LIBOR funding becomes unlawful or impractical) plus (ii) 6.15%, subject to a LIBOR floor of 2.00%. The borrower is required to make interest-only payments on the term loan for all payment dates prior to June 1, 2021. The term loans under the Credit Facility will begin amortizing on June 1, 2021, with equal monthly payments of principal plus interest being made by the Company to the Lenders in consecutive monthly installments following such interest-only period for 36 months or, for any funding of the fourth tranche occurring after June 1, 2021, the number of months until the Credit Facility matures on May 1, 2024. Upon final repayment of the term loans, the borrower must pay an exit fee of 1.75% of the amount borrowed under the Credit Facility, less any partial exit fees previously paid. Upon partial prepayment of a portion of the term loans, the borrower must pay a partial exit fee of 1.75% of the principal being prepaid. At the borrower’s option, the borrower may prepay the outstanding principal balance of the term loan in whole or in part, subject to a prepayment fee of 3.0% of any amount prepaid if the prepayment occurs through and including the first anniversary of the closing date, 2.0% of the amount prepaid if the prepayment occurs after the first anniversary of the closing date through and including the second anniversary of the closing date, and 1.0% of any amount prepaid after the second anniversary of the closing date and prior to May 1, 2024.

The Credit Facility includes affirmative and negative covenants applicable to the Company and certain of its subsidiaries. The affirmative covenants include, among others, covenants requiring such entities to maintain their legal existence and governmental approvals, deliver certain financial reports, maintain insurance coverage, maintain property, pay taxes, satisfy certain requirements regarding accounts and comply with laws and regulations. The negative covenants include, among others, restrictions on such entities from transferring collateral, incurring additional indebtedness, engaging in mergers or acquisitions, paying dividends or making other distributions, making investments, creating liens, amending material agreements and organizational documents, selling assets and suffering a change in control, in each case subject to certain exceptions. The Company and certain of its subsidiaries are also subject to an ongoing minimum cash financial covenant in which they must maintain unrestricted cash in an amount not less than 25% of the outstanding principal amount of the term loans. As of December 31, 2019, the Company was in compliance with these covenants.

The Credit Facility also includes events of default, the occurrence and continuation of which could cause interest to be charged at the rate that is otherwise applicable plus 3.0% and would provide MidCap, as agent, with the right to exercise remedies against the Company and/or certain of its subsidiaries, and the collateral securing the Credit Facility, including foreclosure against the properties securing the credit facilities, including cash. These events of default include, among other things, failure to pay any amounts due under the Credit Facility, a breach of covenants under the Credit Facility, insolvency or the occurrence of insolvency events, the occurrence of a change in control, the occurrence of certain U.S. Food and Drug Administration (“FDA”) and regulatory events, failure to remain registered with the SEC and listed for trading on Nasdaq, the occurrence of a material adverse change, the occurrence of a default under a material agreement reasonably expected to result in a material adverse change, the occurrence of certain defaults under certain other indebtedness in an amount greater than $2,500,000 and the occurrence of certain defaults under subordinated indebtedness and convertible indebtedness.

Long-term debt as of December 31, 2019 consisted of the following (in thousands):

	December 31, 2019
Term loan	$	30,000
Debt discount and issuance costs		(1,541	)
Long-term debt	$	28,459

The scheduled future minimum principal payments are as follows (in thousands):

	December 31, 2019
2020		—
2021		5,833
2022		10,000
2023		10,000
2024		4,167
Total	$	30,000

Convertible Note Financing

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Convertible Note Financing

Note 6—Convertible Note Financing

On October 2, 2017, the Company issued a convertible promissory note (the “Note”) in an amount of $6.0 million to an investor. The Note accrued interest at 8% per year and had a maturity date of October 2, 2018. The Note was subject to an automatic conversion upon a qualified equity financing defined as a raise of $40.0 million, excluding the conversion of the Note and other indebtedness. The conversion was equal to the outstanding principal amount of the Note plus all accrued and previously unpaid interest thereon, divided by the lowest price per share paid by investor for qualified equity financing. On January 4, 2018, the Note converted into 3,499,209 shares of Series A Convertible Preferred Stock.

License and Asset Acquisitions

12 Months Ended

Dec. 31, 2019

Business Combinations [Abstract]

License and Asset Acquisitions

Note 7—License and Asset Acquisitions

The following purchased assets were accounted for as asset acquisitions as substantially all of the fair value of the assets acquired were concentrated in a group of similar assets and/or the acquired assets were not capable of producing outputs due to the lack of employees and early stage of development. Because the assets had not yet received regulatory approval, the fair value attributable to these assets was recorded as in process research and development (“IPR&D”) expenses in the Company’s consolidated statement of operations for the years ended December 31, 2019, 2018, and 2017.

The Company accounts for contingent consideration payable upon achievement of certain regulatory, development or sales milestones in such asset acquisitions when the underlying contingency is resolved.

License from Pulmokine, Inc. (GB002)

On October 2, 2017, the Company, entered into a license agreement with Pulmokine, Inc. under which it was granted an exclusive worldwide license and sublicense to certain intellectual property rights owned or controlled by Pulmokine to develop and commercialize GB002 and certain backup compounds for the treatment, prevention and diagnosis of any and all disease or conditions. The Company also has the right to sublicense its rights under the license agreement, subject to certain conditions. The assets acquired are in the early stages of the FDA approval process, and the Company intends to further develop the assets acquired through potential FDA approval as evidenced by the milestone arrangement in the contract. The development activities cannot be performed without significant cost and effort by the Company. The agreement will remain in effect from the effective date, unless terminated earlier, until, on a licensed product-by-licensed product and country-by-country basis, the later of ten years from the date of first commercial sale or when there is no longer a valid patent claim covering such licensed product or specified regulatory exclusivity for the licensed product in such country. The Company is obligated to make future development and regulatory milestone payments of up to $63.0 million, commercial milestone payments of up to $45.0 million, and sales milestone payments of up to $190.0 million. The Company is also obligated to pay tiered royalties on sales for each licensed product, at percentages ranging from the mid-single digits to the high single-digits. The Company made an upfront payment in the year ended December 31, 2017, recorded as IPR&D of $5.5 million. As of December 31, 2019, no milestones had been accrued as the underlying contingencies had not yet been resolved.

AA Biopharma Inc. Acquisition (GB001)

On January 4, 2018, the Company acquired AA Biopharma Inc. pursuant to a merger agreement, and with the acquisition acquired the rights to GB001 and certain backup compounds. In connection with the merger agreement, the Company issued an aggregate of 20,000,000 shares of Series Seed Convertible Preferred Stock and 1,101,278 shares of Common Stock to the AA Biopharma shareholders. The Company recorded IPR&D of $19.3 million in connection with the acquisition of AA Biopharma.

License from Aerpio Pharmaceuticals, Inc. (GB004)

On June 24, 2018, the Company entered into a license agreement with Aerpio Pharmaceuticals, Inc. (“Aerpio”) under which the Company was granted an exclusive worldwide license and sublicense to certain intellectual property rights owned or controlled by Aerpio to develop and commercialize GB004, and certain other related compounds for all applications. The Company also has the right to sublicense its rights under the license agreement, subject to certain conditions. The Company is obligated to make future development and regulatory milestone payments of up to $55.0 million, commercial milestone payments of up to $85.0 million and sales milestone payments of up to $260.0 million. The Company is also obligated to pay tiered royalties on sales for each licensed product, at percentages ranging from a high single-digit to mid-teens, subject to certain customary reductions. The Company made an upfront payment of $20.0 million, which represented the purchase consideration for an asset acquisition. As of December 31, 2019, no milestones had been accrued as the underlying contingencies had not yet been resolved.

Adhaere Pharmaceuticals, Inc. Acquisition (GB1275)

On September 21, 2018, the Company acquired Adhaere Pharmaceuticals, Inc. pursuant to a merger agreement for an upfront payment of $7.5 million in cash, and with the acquisition acquired the rights to GB1275 and certain backup compounds. The Company is obligated to make future regulatory, development and sales milestone payments of up to $62.0 million and pay tiered royalties on worldwide net sales, at percentages ranging from low to mid-single digits, subject to customary reductions. The Company recorded IPR&D of $7.5 million in connection with the acquisition of Adhaere. In May 2019, the Company made a milestone payment of $1.0 million in connection with the filing of the Investigational New Drug application for the GB1275 program. As of December 31, 2019, no other milestones had been accrued as the underlying contingencies had not yet been resolved.

The Company recorded the following IPR&D expense on the consolidated statements of operations (in thousands):

	Years Ended December 31,
	2019		2018		2017
GB002	$	—	$	—	$	5,500
GB001		—		19,148		—
GB004		—		20,000		—
GB1275		1,000		7,501		—
Other preclinical programs		2,600		3,010		—
Total in process research and development	$	3,600	$	49,659	$	5,500

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

Note 8—Income Taxes

The amount of net loss before taxes for the years ended December 31, 2019, 2018, and 2017 is as follows:

	December 31,
	2019		2018		2017
	(in thousands)
U.S. loss before taxes	$	138,342	$	116,920	$	6,771
Foreign loss before taxes		41,965		30,049		—
Loss before income taxes		180,307		146,969		6,771

A reconciliation of income tax expense for the years ended December 31, 2019, 2018, and 2017 is as follows:

	December 31,
	2019		2018		2017
	(in thousands)
Current:
Federal	$	—	$	—	$	—
State		—		—		—
Foreign		—		—		—
Total current income tax expense		—		—		—

Deferred:
Federal	$	—	$	—	$	—
State		—		—		—
Foreign		—		—		—
Total deferred income tax expense		—		—		—
Total income tax expense	$	—	$	—	$	—

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets and liabilities at December 31, 2019, 2018 and 2017 are shown below. The Company has established a valuation allowance against net deferred tax assets due to the uncertainty that such assets will be realized. The Company periodically evaluates the recoverability of the deferred assets. At such time as it is determined that it is more likely than not that the deferred tax asset will be realized, the valuation allowance will be reduced. The change in the valuation allowance for the year ended December 31, 2019 was an increase of $41.0 million.

	December 31,
	2019			2018			2017
	(in thousands)
Deferred tax assets:
Net operating losses	$	43,626		$	14,442		$	306
Tax credits, net		9,196			1,131			—
Amortization		6,597			6,267			1,588
Lease liability		2,329			—			—
Accrued compensation		1,476			834			—
Stock-based compensation		1,388			—			1
Other		383			154			—
Total gross deferred tax assets		64,995			22,828			1,895

Deferred tax liabilities:
Right of use asset		(2,164	)		—			—
Property, plant and equipment		(57	)		(16	)		—
Stock-based compensation		—			(1,057	)		—
Total gross deferred tax liabilities		(2,221	)		(1,073	)		—

Valuation allowance		(62,774	)		(21,755	)		(1,895	)
Net deferred tax asset	$	—		$	—		$	—

At December 31, 2019, the Company has federal and California net operating losses (“NOL”) carryforwards of approximately $175.8 million and $1.1 million, respectively. The federal NOL carryforwards generated prior to January 1, 2018 begin to expire in 2034. The federal NOL generated after 2017 of $172.9 million can be carried forward indefinitely and be available to offset up to 80% of future taxable income each year. The California NOL carryforwards begin to expire in 2036. At December 31, 2019, the Company has Irish NOL carryforwards of approximately $53.0 million. The Irish NOL can be carried forward indefinitely.

At December 31, 2019, the Company also has orphan drug credit and federal research tax credit carryforwards of approximately $9.6 million and California research tax credits of $2.7 million. The federal research tax credit carryforwards begin to expire in 2038 and the California research tax credit carryforward does not expire and can be carried forward indefinitely until utilized.

A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	December 31,
	2019	2018	2017
Federal statutory income tax rate	21.00%	21.00%	34.00%
State income taxes, net of federal benefit	—%	—%	5.73%
Change in valuation allowance	(22.12%)	(13.17%)	(27.97%)
Change in tax law	—%	—%	(11.85%)
Research and experimentation credits	3.81%	0.77%	—%
Foreign rate differential	(1.84%)	(1.74%)	—%
Stock-based compensation	—%	(2.60%)	—%
In process research and development	—%	(3.92%)	—%
Other	(0.85%)	(0.34%)	0.09%
Provision for income taxes	—%	—%	—%

The NOL carryforward may be subject to an annual limitation under Section 382 and 383 of the Internal Revenue Code of 1986 (the “Code”), and similar state provisions if the Company experienced one or more ownership changes which would limit the amount of NOL and tax credit carryforwards that can be utilized to offset future taxable income and tax respectively. In general, an ownership change as defined by Section 382 and 383, results from the transactions increasing ownership of certain stockholders or public groups in the stock of the corporation of more than 50 percentage points over a three-year period. As of December 31, 2019, the Company completed a Section 382 and 383 analysis regarding the limitation of NOL and credit carryforwards. In connection with the Company’s IPO in February 2019, the Company experienced an ownership change for the purposes of Section 382 and 383 of the Code. The ownership change did not result in the forfeiture of any NOLs or credits generated prior to this date. Consequently, the Company’s federal and state NOLs and tax credits generated through February 2019 will be subject to annual limitations. If a change in ownership occurs in the future, the NOL and tax credits carryforwards could be eliminated or restricted. If eliminated, the related asset would be removed from the deferred tax asset schedule with a corresponding reduction in the valuation allowance. Due to the existence of the valuation allowance, limitations created by future ownership changes, if any, will not impact the Company’s effective tax rate.

The Company files income tax returns in the United States, California, Ireland, and Luxembourg. Due to the Company’s unutilized NOLs and credits, the Company is subject to the income tax examination by authorities since inception. The Company’s policy is to recognize interest expense and penalties related to income tax matters as tax expense. As of December 31, 2019, 2018, or 2017, there were no significant accruals for interest related to unrecognized tax benefits or tax penalties.

On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (“Tax Act”) was signed into law making significant changes to the Internal Revenue Code, including, but are not limited to (a) reducing the federal corporate income tax rate from 35% to 21%, effective January 1, 2018; (b) eliminating the federal corporate alternative minimum tax (“AMT”) and changing how existing AMT credits can be realized; and (c) eliminating several business deductions and credits, including deductions for certain executive compensation in excess of $1 million.

As a result of the rate reduction, the Company reduced the deferred tax asset balance as of December 31, 2017 by $0.8 million. Due to the Company's full valuation allowance position, there was no net impact on the Company’s income tax provision at December 31, 2017 as the reduction in the deferred tax asset balance was fully offset by a corresponding decrease in the valuation allowance.

A reconciliation of the beginning and ending amount of unrecognized tax benefits for 2019, 2018, and 2017, excluding interest and penalties, is as follows:

	December 31,
	2019		2018		2017
	(in thousands)
Balance at beginning of the year	$	408	$	—	$	—
Increase related to current year positions		2,346		408		—
Balance at the end of the year	$	2,754	$	408	$	—

Included in the balance of unrecognized tax benefits at December 31, 2019 is $2.6 million that, if recognized, would not impact the Company’s income tax benefit or effective tax rate as long as our deferred tax asset remains subject to a full valuation allowance. The Company does not expect any significant increases or decreases to our unrecognized tax benefits within the next 12 months.

Convertible Preferred Stock and Stockholders' Equity (Deficit)

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Convertible Preferred Stock and Stockholders' Equity (Deficit)

Note 9—Convertible Preferred Stock and Stockholders’ Equity (Deficit)

Convertible Preferred Stock

Series Seed Convertible Preferred Stock

On January 4, 2018, the Company issued an aggregate of 20,000,000 shares of Series Seed Convertible Preferred Stock in connection with the merger agreement with AA Biopharma Inc. (See Note 7).

Series A Convertible Preferred Stock

In January and March 2018, the Company issued an aggregate of 45,714,286 shares of Series A Convertible Preferred Stock at $1.75 per share for approximately $73.9 million in cash and the conversion of approximately $6.1 million in principal and accrued interest under the Note (See Note 6).

Series B Convertible Preferred Stock

On July 20, 2018, the Company issued an aggregate of 71,506,513 shares of Series B Convertible Preferred Stock at $3.2167 per share for approximately $230.0 million in gross proceeds.

The Series Convertible Preferred Stock was classified outside of stockholders’ equity (deficit) because the shares contained certain redemption features that were not solely within the control of the Company. In connection with the Company’s IPO, the outstanding shares of the Company’s Series Seed, Series A, and Series B Convertible Preferred Stock automatically converted into 30,493,460 shares of common stock.

Common Stock

On December 3, 2015, the Company issued 9,160,888 shares of common stock as founder shares for services rendered to the Company, valued at $0.0001 par value per share, for a total of approximately $4,100 (the “Founders’ Equity”). On January 4, 2018, incremental vesting conditions were placed on the previously issued founder shares. Fifty percent of the previously issued founder shares vested on January 4, 2018, and the remaining founder shares are subject to vesting restrictions over a period of five years.

Pursuant to the employment agreements with the Company’s founders executed January 4, 2018, the Company provided for certain potential additional issuances of common stock (the “anti-dilution shares”) to each of the founders to ensure the total number of shares of common stock held by them and their affiliates (inclusive of any shares subject to equity awards granted by the Company and the Founders’ Equity) would represent 15% of the Company’s fully-diluted capitalization until such time as the Company raised $300 million in equity capital, including the capital raised in the Series A financing.

In furtherance of this obligation, on May 21, 2018, the Company issued 251,547 shares of common stock to the founders for services rendered to the Company, valued at $2.61 per share with an additional 251,547 shares of restricted stock subject to the same vesting restrictions and vesting period as the founder shares. In addition, on September 6, 2018, the Company issued 1,795,023 shares of common stock to the founders for services rendered to the Company, valued at $9.63 per share, with an additional 1,795,023 shares of restricted stock subject to the same vesting restrictions and vesting period as the founder shares.

Each share of common stock is entitled to one voting right. Common stock owners are entitled to dividends when funds are legally available and declared by the Board.

Shares of Common Stock Subject to Repurchase

In November 2017, in connection with the issuance of the Series A Convertible Preferred Stock, certain employees entered into stock restriction agreements, whereby 1,305,421 shares are subject to forfeiture by the Company upon the stockholder’s termination of employment or service to the Company. In January 2018, the Company’s founders entered into stock restriction agreements, whereby 4,580,444 of previously unrestricted shares of common stock were subject to service vesting conditions. These shares are also subject to forfeiture by the Company upon the stockholders’ termination of employment or service to the Company. Any shares subject to repurchase by the Company are not deemed, for accounting purposes, to be outstanding until those shares vest. As such, the Company recognizes the measurement date fair value of the restricted stock over the vesting period as compensation expense. For the years ended December 31, 2019, 2018 and 2017, 4,648,526 shares, 7,482,032 shares and 1,305,421 shares of common stock, respectively, were subject to repurchase by the Company. The unvested stock liability related to these awards is immaterial to all periods presented.

Equity Incentive Plans

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity Incentive Plans

Note 10—Equity Incentive Plans

Approval of the 2019 Equity Incentive Plan

In January 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Incentive Award Plan (the “2019 Plan”). The 2019 Plan became effective on February 6, 2019, the day prior to the effectiveness of the registration statement filed in connection with the IPO. Under the 2019 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units, and other stock or cash-based awards to individuals who are then employees, officers, directors or consultants of the Company, and employees and consultants of the Company’s subsidiaries. A total of 5,750,000 shares of common stock were approved to be initially reserved for issuance under the 2019 Plan. The number of shares that remained available for issuance under the 2017 Plan (as defined below) as of the effective date of the 2019 Plan were, and shares subject to outstanding awards under the 2017 Plan as of the effective date of the 2019 Plan that are subsequently canceled, forfeited or repurchased by the Company will be added to the shares reserved under the 2019 Plan. In addition, the number of shares of common stock available for issuance under the 2019 Plan will be automatically increased on the first day of each calendar year during the ten-year term of the 2019 Plan, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 5% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. As of December 31, 2019, an aggregate of 1,751,485 shares of common stock were available for issuance under the 2019 Plan and 4,003,040 shares of common stock were subject to outstanding options under the 2019 Plan.

Approval of the 2019 Employee Stock Purchase Plan

In January 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Employee Stock Purchase Plan (the “ESPP”). The ESPP became effective as of February 6, 2019, the day prior to the effectiveness of the registration statement filed in connection with the IPO. The ESPP permits participants to purchase common stock through payroll deductions of up to 20% of their eligible compensation. A total of 700,000 shares of common stock were approved to be initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP will be automatically increased on the first day of each calendar year during the first ten-years of the term of the ESPP, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 1% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. As of December 31, 2019, an aggregate of 700,000 shares of common stock were available for issuance under the ESPP.

2017 Equity Incentive Plan

The Company’s 2017 Equity Incentive Plan (the “2017 Plan”) permitted the granting of incentive stock options, non-statutory stock options, restricted stock, restricted stock units and other stock-based awards. Subsequent to the adoption of the 2019 Plan, no additional equity awards can be made under the 2017 Plan. As of December 31, 2019, 4,535,020 shares of common stock were subject to outstanding options under the 2017 Plan, and 561,868 shares of restricted stock awards granted under the 2017 plan were unvested.

Fair Value of Stock Option Awards

The fair value of each employee and non-employee stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company, prior to the IPO on February 12, 2019, was a private company and lacked company-specific historical and implied volatility information. Therefore, it estimated its expected volatility based on the historical volatility of a publicly traded set of peer companies. Due to the lack of historical exercise history, the expected term of the Company’s stock options for employees has been determined utilizing the “simplified” method for awards. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

The following assumptions were used to estimate the fair value of stock option awards granted to employees under the Company’s equity incentive plans and the shares purchasable under the ESPP during the periods presented:

Year Ended December 31,

2019

2018

2017

Employee Stock Options

Expected term (in years)

4.6 - 6.1

5.3 - 6.1

N/A

Risk-free interest rate

1.38% - 2.58%

2.65% - 2.96%

N/A

Volatility

70.25% - 86.92%

69.13% - 77.62%

N/A

Dividend yield

–

N/A

Employee Stock Purchase Plan

Expected term (in years)

0.49 - 1.99

N/A

Risk-free interest rate

1.46% - 1.87%

N/A

Volatility

72.08% - 78.70%

N/A

Dividend yield

–

N/A

Stock Options

The following table summarizes stock option activity for the years ended December 31, 2019 and 2018:

	Shares Subject to Options Outstanding					Weighted- Average
				Weighted-		Remaining
				Average Exercise		Contractual Life		Aggregate
	Shares			Price		(Years)		Intrinsic Value
								(in thousands)
Outstanding as of December 31, 2017		—			—		—	$	—
Options granted		5,143,551		$	7.49
Option exercised		—		$	—
Options forfeited/cancelled		(36,222	)	$	4.85
Outstanding as of December 31, 2018		5,107,329		$	7.51		9.7	$	16,343
Options granted		4,194,624		$	20.11
Option exercised		(419,593	)	$	4.87
Options forfeited/cancelled		(344,300	)	$	11.64
Outstanding as of December 31, 2019		8,538,060		$	13.67		9.0	$	35,385
Options vested and exercisable as of December 31, 2019		1,215,471		$	7.25		8.7	$	10,183

No stock options were granted for the year ended December 31, 2017.

The weighted-average grant date fair value per share for the stock options granted during the year ended December 31, 2019 and 2018 was $13.17 and $4.87, respectively.

The aggregate fair value of stock options that vested during the years ended December 31, 2019 and 2018 was $7.2 million and $0.1 million, respectively.

The aggregate intrinsic value in the above table is calculated as the difference between fair value of the Company’s common stock price and the exercise price of the stock options. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2019 was $6.9 million. There were no stock options exercised during the year ended December 31, 2018.

At December 31, 2019, the total unrecognized compensation related to unvested stock option awards granted was $61.0 million, which the Company expects to recognize over a weighted-average period of approximately 2.9 years.

Restricted Stock

The summary of the Company’s restricted stock activity during the years ended December 31, 2019, 2018 and 2017 is as follows:

	Number of			Weighted-
	Restricted			Average
	Stock Units			Grant Date
	Outstanding			Fair Value
Nonvested at December 31, 2016		—		$	—
Granted		1,305,421			0.09
Nonvested at December 31, 2017		1,305,421		$	0.09
Granted		8,673,584			5.53
Vested		(2,369,696	)		7.58
Forfeited		(127,277	)		0.09
Nonvested at December 31, 2018		7,482,032		$	4.01
Granted		—			—
Vested		(2,833,506	)		4.05
Forfeited		—			—
Nonvested at December 31, 2019		4,648,526		$	3.98

At December 31, 2019, the total unrecognized compensation related to unvested restricted stock awards granted was $13.5 million, which the Company expects to recognize over a weighted-average period of approximately 2.8 years.

Stock-Based Compensation Expense

Stock-based compensation expense has been reported in the Company’s consolidated statements of operations as follows (in thousands):

	Year Ended
	December 31,
	2019		2018		2017
Research and development	$	10,227	$	679	$	17
General and administrative		10,592		30,268		15
Total stock-based compensation	$	20,819	$	30,947	$	32

As of December 31, 2019, total unrecognized compensation expense related to the ESPP was $1.3 million, which the Company expects to recognize over a weighted-average period of approximately 1.1 years.

Property and Equipment, Net

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Property and Equipment, Net

Note 11—Property and Equipment, Net

The Company’s property and equipment, net consisted of the following (in thousands):

	Estimated Useful Life (in years)	December 31, 2019		December 31, 2018
Office equipment	3-7	$	1,097	$	918
Computer equipment	5		124		15
Software	3		87		50
Lab equipment	2-5		3,054		1,070
Leasehold improvements	6-7		2,229		1,243
Construction in process	N/A		48		194
Total property and equipment			6,639		3,490
Less: accumulated depreciation			1,214		297
Property and equipment, net		$	5,425	$	3,193

Depreciation expense for the years ended December 31, 2019 and December 31, 2018 was approximately $0.9 million and $0.3 million, respectively, and was recorded in general and administrative expense in the Consolidated Statements of Operations. No depreciation expense was recorded for the year ended December 31, 2017.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 12—Commitments and Contingencies

Leases

The Company subleases certain office and laboratory space under a non-cancelable operating lease expiring in January 2025 for the initial leased space and December 2022 for expansion space leased pursuant to an amendment to the lease agreement entered into in August 2018. The sublease agreement included options to extend for the entire premises through October 2028. The options to extend must be exercised prior to the termination of the original lease agreement. The period covered by the options was not included in the non-cancellable lease term as it not was not determined to be reasonably certain to be executed. The lease agreement also includes a one-time termination option for the expansion space only whereby the Company can terminate the lease with advance written notice. The termination option was not determined to be reasonably certain to be executed. The lease is subject to charges for common area maintenance and other costs, and base rent is subject to an annual 3% increase each subsequent year. Costs determined to be variable and not based on an index or rate were not included in the measurement of the operating lease liabilities.

In November 2019, the Company entered into an additional non-cancelable lease agreement for certain office and laboratory space (the “permanent space”) in San Diego, California, commencing on May 1, 2020 and expiring on December 31, 2021. The lease agreement includes a lease for temporary space commencing on January 1, 2020 and expiring on the commencement date of the lease of the permanent space. The monthly base rent for the permanent and temporary space is $63,425 and $28,745, respectively. The lease agreement included an option to extend the term of the permanent space for twelve months. The option to extend must be exercised nine months prior to the termination of the original lease agreement. The period covered by the option was not included in the non-cancellable lease term as it not was not determined to be reasonably certain to be executed. The lease is subject to charges for common area maintenance and other costs, and base rent is subject to an annual 3% increase each subsequent year.

Monthly rent expense is recognized on a straight-line basis over the term of the leases. The operating leases are included in the balance sheet at the present value of the lease payments at a weighted average discount rate of 7% using the rate of interest that the Company would have to pay to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment as the leases do not provide an implicit rate. The weighted average remaining lease term was 4.0 years.

Lease costs were comprised of the following (in thousands):

	Year ended December 31, 2019
Operating lease cost	$	3,011
Short-term lease cost		133
Total lease cost	$	3,144

Cash paid for amounts included in the measurement of operating lease liabilities for the year ended December 31, 2019 was $3.0 million.

Gross future minimum annual rental commitments as of December 31, 2019, were as follows (in thousands):

	Undiscounted Rent Payments
Year ending December 31,
2020		3,038
2021		3,127
2022		3,220
2023		1,694
2024		1,745
Total undiscounted rent payments	$	12,824

Present value discount		(1,733	)
Present value	$	11,091
Current portion of operating lease liabilities (included as a component of accrued expenses and other current liabilities)	$	2,354
Noncurrent operating lease liabilities		8,737
Total operating lease liability	$	11,091

Future minimum payments under the non-cancelable operating lease as of December 31, 2018 were as follows (in thousands):

Years ending December 31,
2019		2,944
2020		3,035
2021		3,123
2022		3,216
2023		1,690
Thereafter		1,741
	$	15,749

For the years ended December 31, 2019 and December 31, 2018, the Company recorded approximately $3.1 million and $1.5 million, respectively, in rent expense. The sublease did not commence until January 15, 2018, therefore there was no rent expense for the year ended December 31, 2017.

Litigation

The Company is not a party to any material legal proceedings and is not aware of any pending or threatened claims. From time to time, the Company may be subject to various legal proceedings and claims that arise in the ordinary course of its business activities.

Selected Quarterly Financial Information (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Information (Unaudited)

Note 13—Selected Quarterly Financial Information (Unaudited)

The following is a summary of the quarterly results of the Company for the years ended December 31, 2019 and 2018 (unaudited, in thousands, except for per share data):

	Year Ended December 31, 2019
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Operating loss		(34,017	)		(46,349	)		(49,986	)		(55,787	)
Net loss		(32,611	)		(44,498	)		(48,500	)		(54,698	)
Per common share:
Loss per share, basic and diluted		(0.90	)		(0.74	)		(0.80	)		(0.89	)

	Year Ended December 31, 2018
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Operating loss		(26,126	)		(33,036	)		(50,024	)		(39,807	)
Net loss		(26,037	)		(32,729	)		(49,409	)		(38,794	)
Per common share:
Loss per share, basic and diluted		(4.31	)		(5.52	)		(8.03	)		(4.92	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Segments

Cash and Cash Equivalents

Marketable Securities

Restricted Cash

The Company had no restricted cash as of December 31, 2019. Restricted cash as of December 31, 2018 served as collateral for the Company’s corporate credit card program.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Property and Equipment, Net

Deferred Offering Costs

Leases

Research and Development

Patent Costs

Income Taxes

Stock-Based Compensation

Foreign Currency

Recently Adopted Accounting Pronouncements

Recent Accounting Pronouncements—To Be Adopted

Recently Adopted Accounting Pronouncements

Net Loss Per Share

The table below provides potentially dilutive securities not included in the calculation of the diluted net loss per share because to do so would be anti-dilutive:

	December 31,
	2019		2018		2017
Shares issuable upon conversion of Series Seed Convertible Preferred Stock		—		4,444,444		—
Shares issuable upon conversion of Series A Convertible Preferred Stock		—		10,158,710		—
Shares issuable upon conversion of Series B Convertible Preferred Stock		—		15,890,306		—
Shares issuable upon exercise of stock options		8,538,060		5,107,329		—
Non-vested shares under restricted stock grants		4,648,526		7,482,032		1,305,421

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share

The table below provides potentially dilutive securities not included in the calculation of the diluted net loss per share because to do so would be anti-dilutive:

	December 31,
	2019		2018		2017
Shares issuable upon conversion of Series Seed Convertible Preferred Stock		—		4,444,444		—
Shares issuable upon conversion of Series A Convertible Preferred Stock		—		10,158,710		—
Shares issuable upon conversion of Series B Convertible Preferred Stock		—		15,890,306		—
Shares issuable upon exercise of stock options		8,538,060		5,107,329		—
Non-vested shares under restricted stock grants		4,648,526		7,482,032		1,305,421

Accrued Expenses and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	Years Ended December 31,
	2019		2018
Accrued compensation	$	9,282	$	4,102
Operating lease liabilities, current		2,354		—
Accrued in process research and development		1,600		—
Accrued consulting fees		1,337		665
Accrued other		1,126		769
Accrued legal fees		837		1,310
Accrued accounting fees		173		722
Total accrued expenses	$	16,709	$	7,568

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Assets Measured at Fair Value on Recurring Basis

The following table presents the hierarchy for assets measured at fair value on a recurring basis as of December 31, 2019 and December 31, 2018 (in thousands):

	Fair Value Measurements at End of Period Using:
			Quoted Market		Significant		Significant
			Prices for		Other Observable		Unobservable
	Total		Identical Assets		Inputs		Inputs
	Fair Value		(Level 1)		(Level 2)		(Level 3)
As of December 31, 2019
Money market funds	$	82,125	$	82,125	$	—	$	—
U.S. Treasury and agency securities		91,717		91,717		—		—
Commercial paper		37,411		—		37,411		—
Corporate debt securities		156,277		—		156,277		—
As of December 31, 2018
Money market funds	$	17,295	$	17,295	$	—	$	—
U.S. Treasury securities		123,439		123,439		—		—

Schedule of Available for Sale Investments by Security Type

			Gross		Gross
	Amortized		Unrealized		Unrealized			Total
	Cost		Gains		Losses			Fair Value
Marketable securities
U.S. Treasury and agency securities	$	77,993	$	57	$	—		$	78,050
Commercial paper		32,413		—		—			32,413
Corporate debt securities		156,059		238		(20	)		156,277
Total marketable securities	$	266,465	$	295	$	(20	)	$	266,740

Schedule of Contractual Maturities of Available-for-sale Debt Securities

Contractual maturities of available-for-sale debt securities, as of December 31, 2019, were as follows (in thousands):

	Estimated
	Fair Value
Due within one year	$	237,449
One to two years		29,291
Total	$	266,740

Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Schedule of Long-Term Debt

Long-term debt as of December 31, 2019 consisted of the following (in thousands):

	December 31, 2019
Term loan	$	30,000
Debt discount and issuance costs		(1,541	)
Long-term debt	$	28,459

Schedule of Future Minimum Principal Payments

The scheduled future minimum principal payments are as follows (in thousands):

	December 31, 2019
2020		—
2021		5,833
2022		10,000
2023		10,000
2024		4,167
Total	$	30,000

License and Asset Acquisitions (Tables)

12 Months Ended

Dec. 31, 2019

Business Combinations [Abstract]

Schedule of IPR&D Expense

The Company recorded the following IPR&D expense on the consolidated statements of operations (in thousands):

	Years Ended December 31,
	2019		2018		2017
GB002	$	—	$	—	$	5,500
GB001		—		19,148		—
GB004		—		20,000		—
GB1275		1,000		7,501		—
Other preclinical programs		2,600		3,010		—
Total in process research and development	$	3,600	$	49,659	$	5,500

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Amount of Net Loss Before Taxes

The amount of net loss before taxes for the years ended December 31, 2019, 2018, and 2017 is as follows:

	December 31,
	2019		2018		2017
	(in thousands)
U.S. loss before taxes	$	138,342	$	116,920	$	6,771
Foreign loss before taxes		41,965		30,049		—
Loss before income taxes		180,307		146,969		6,771

Schedule of Reconciliation of Income Tax Expense

A reconciliation of income tax expense for the years ended December 31, 2019, 2018, and 2017 is as follows:

	December 31,
	2019		2018		2017
	(in thousands)
Current:
Federal	$	—	$	—	$	—
State		—		—		—
Foreign		—		—		—
Total current income tax expense		—		—		—

Deferred:
Federal	$	—	$	—	$	—
State		—		—		—
Foreign		—		—		—
Total deferred income tax expense		—		—		—
Total income tax expense	$	—	$	—	$	—

Schedule of Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and liabilities at December 31, 2019, 2018 and 2017 are shown below.

	December 31,
	2019			2018			2017
	(in thousands)
Deferred tax assets:
Net operating losses	$	43,626		$	14,442		$	306
Tax credits, net		9,196			1,131			—
Amortization		6,597			6,267			1,588
Lease liability		2,329			—			—
Accrued compensation		1,476			834			—
Stock-based compensation		1,388			—			1
Other		383			154			—
Total gross deferred tax assets		64,995			22,828			1,895

Deferred tax liabilities:
Right of use asset		(2,164	)		—			—
Property, plant and equipment		(57	)		(16	)		—
Stock-based compensation		—			(1,057	)		—
Total gross deferred tax liabilities		(2,221	)		(1,073	)		—

Valuation allowance		(62,774	)		(21,755	)		(1,895	)
Net deferred tax asset	$	—		$	—		$	—

Reconciliation of the Federal Statutory Income Tax Rate to Effective Income Tax Rate

A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	December 31,
	2019	2018	2017
Federal statutory income tax rate	21.00%	21.00%	34.00%
State income taxes, net of federal benefit	—%	—%	5.73%
Change in valuation allowance	(22.12%)	(13.17%)	(27.97%)
Change in tax law	—%	—%	(11.85%)
Research and experimentation credits	3.81%	0.77%	—%
Foreign rate differential	(1.84%)	(1.74%)	—%
Stock-based compensation	—%	(2.60%)	—%
In process research and development	—%	(3.92%)	—%
Other	(0.85%)	(0.34%)	0.09%
Provision for income taxes	—%	—%	—%

Schedule of Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits, Excluding Interest and Penalties

A reconciliation of the beginning and ending amount of unrecognized tax benefits for 2019, 2018, and 2017, excluding interest and penalties, is as follows:

	December 31,
	2019		2018		2017
	(in thousands)
Balance at beginning of the year	$	408	$	—	$	—
Increase related to current year positions		2,346		408		—
Balance at the end of the year	$	2,754	$	408	$	—

Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Fair Value of Stock Option Award Granted

Year Ended December 31,

2019

2018

2017

Employee Stock Options

Expected term (in years)

4.6 - 6.1

5.3 - 6.1

N/A

Risk-free interest rate

1.38% - 2.58%

2.65% - 2.96%

N/A

Volatility

70.25% - 86.92%

69.13% - 77.62%

N/A

Dividend yield

–

N/A

Employee Stock Purchase Plan

Expected term (in years)

0.49 - 1.99

N/A

Risk-free interest rate

1.46% - 1.87%

N/A

Volatility

72.08% - 78.70%

N/A

Dividend yield

–

N/A

Summary of Stock Option Activity

Stock Options

The following table summarizes stock option activity for the years ended December 31, 2019 and 2018:

	Shares Subject to Options Outstanding					Weighted- Average
				Weighted-		Remaining
				Average Exercise		Contractual Life		Aggregate
	Shares			Price		(Years)		Intrinsic Value
								(in thousands)
Outstanding as of December 31, 2017		—			—		—	$	—
Options granted		5,143,551		$	7.49
Option exercised		—		$	—
Options forfeited/cancelled		(36,222	)	$	4.85
Outstanding as of December 31, 2018		5,107,329		$	7.51		9.7	$	16,343
Options granted		4,194,624		$	20.11
Option exercised		(419,593	)	$	4.87
Options forfeited/cancelled		(344,300	)	$	11.64
Outstanding as of December 31, 2019		8,538,060		$	13.67		9.0	$	35,385
Options vested and exercisable as of December 31, 2019		1,215,471		$	7.25		8.7	$	10,183

Summary of Restricted Stock Activity

The summary of the Company’s restricted stock activity during the years ended December 31, 2019, 2018 and 2017 is as follows:

	Number of			Weighted-
	Restricted			Average
	Stock Units			Grant Date
	Outstanding			Fair Value
Nonvested at December 31, 2016		—		$	—
Granted		1,305,421			0.09
Nonvested at December 31, 2017		1,305,421		$	0.09
Granted		8,673,584			5.53
Vested		(2,369,696	)		7.58
Forfeited		(127,277	)		0.09
Nonvested at December 31, 2018		7,482,032		$	4.01
Granted		—			—
Vested		(2,833,506	)		4.05
Forfeited		—			—
Nonvested at December 31, 2019		4,648,526		$	3.98

Stock-Based Compensation Expense Reported in Condensed Consolidated Statements of Operations

Stock-based compensation expense has been reported in the Company’s consolidated statements of operations as follows (in thousands):

	Year Ended
	December 31,
	2019		2018		2017
Research and development	$	10,227	$	679	$	17
General and administrative		10,592		30,268		15
Total stock-based compensation	$	20,819	$	30,947	$	32

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

The Company’s property and equipment, net consisted of the following (in thousands):

	Estimated Useful Life (in years)	December 31, 2019		December 31, 2018
Office equipment	3-7	$	1,097	$	918
Computer equipment	5		124		15
Software	3		87		50
Lab equipment	2-5		3,054		1,070
Leasehold improvements	6-7		2,229		1,243
Construction in process	N/A		48		194
Total property and equipment			6,639		3,490
Less: accumulated depreciation			1,214		297
Property and equipment, net		$	5,425	$	3,193

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of Lease Costs

Lease costs were comprised of the following (in thousands):

	Year ended December 31, 2019
Operating lease cost	$	3,011
Short-term lease cost		133
Total lease cost	$	3,144

Schedule of Gross Future Minimum Annual Rental Commitments

Gross future minimum annual rental commitments as of December 31, 2019, were as follows (in thousands):

	Undiscounted Rent Payments
Year ending December 31,
2020		3,038
2021		3,127
2022		3,220
2023		1,694
2024		1,745
Total undiscounted rent payments	$	12,824

Present value discount		(1,733	)
Present value	$	11,091
Current portion of operating lease liabilities (included as a component of accrued expenses and other current liabilities)	$	2,354
Noncurrent operating lease liabilities		8,737
Total operating lease liability	$	11,091

Schedule of Future Minimum Lease Payments Under Non-Cancelable Operating Leases

Future minimum payments under the non-cancelable operating lease as of December 31, 2018 were as follows (in thousands):

Years ending December 31,
2019		2,944
2020		3,035
2021		3,123
2022		3,216
2023		1,690
Thereafter		1,741
	$	15,749

Selected Quarterly Financial Information (Unaudited) (Table)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Schedule of Selected Quarterly Financial Information (Unaudited)

The following is a summary of the quarterly results of the Company for the years ended December 31, 2019 and 2018 (unaudited, in thousands, except for per share data):

	Year Ended December 31, 2019
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Operating loss		(34,017	)		(46,349	)		(49,986	)		(55,787	)
Net loss		(32,611	)		(44,498	)		(48,500	)		(54,698	)
Per common share:
Loss per share, basic and diluted		(0.90	)		(0.74	)		(0.80	)		(0.89	)

	Year Ended December 31, 2018
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Operating loss		(26,126	)		(33,036	)		(50,024	)		(39,807	)
Net loss		(26,037	)		(32,729	)		(49,409	)		(38,794	)
Per common share:
Loss per share, basic and diluted		(4.31	)		(5.52	)		(8.03	)		(4.92	)

Organization and Basis of Presentation - Additional Information (Detail)				17 Months Ended
	May 02, 2019 USD ($) Tranche	Feb. 12, 2019 USD ($) $ / shares shares	Jan. 04, 2018 USD ($)	Feb. 28, 2019 USD ($)	Dec. 31, 2019 USD ($) Tranche	Dec. 31, 2018 USD ($)
Organization and Basis of Presentation [Line Items]
Accumulated deficit					$ (334,170,000)	$ (153,863,000)
Funds raised through Series A and Series B Convertible Preferred Stock, convertible note financings and completed IPO				$ 601,300,000
Term Loan
Organization and Basis of Presentation [Line Items]
Maximum borrowing capacity	$ 150,000,000
Amount funded	$ 30,000,000
Number of additional tranches executed \| Tranche	3				0
Remaining borrowing capacity	$ 120,000,000
Term Loan \| Tranche One
Organization and Basis of Presentation [Line Items]
Remaining borrowing capacity	40,000,000
Term Loan \| Tranche Two
Organization and Basis of Presentation [Line Items]
Remaining borrowing capacity	30,000,000
Term Loan \| Tranche Three
Organization and Basis of Presentation [Line Items]
Remaining borrowing capacity	$ 50,000,000
AA Biopharma Inc.
Organization and Basis of Presentation [Line Items]
Cash received in connection with acquisition			$ 12,800,000
Initial Public Offering ("IPO")
Organization and Basis of Presentation [Line Items]
Sale of shares of common stock \| shares		19,837,500
Offering price, per share \| $ / shares		$ 16.00
Net proceeds, after deducting underwriting discounts, commissions, and offering expenses		$ 291,300,000

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) segment	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Number of operating segments \| segment	1
Restricted cash	$ 0		$ 200
Deferred offering costs	0		$ 2,100
Operating lease right-of-use assets	10,303
Operating lease liabilities	$ 11,091
Accounting Standards Update 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets		$ 12,500
Operating lease liabilities		$ 13,200

Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares Issuable upon Conversion of Series Seed Convertible
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included from calculation of diluted net loss per share		4,444,444
Shares Issuable upon Conversion of Series A Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included from calculation of diluted net loss per share		10,158,710
Shares Issuable upon Conversion of Series B Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included from calculation of diluted net loss per share		15,890,306
Shares Issuable upon Exercise of Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included from calculation of diluted net loss per share	8,538,060	5,107,329
Non-vested Shares under Restricted Stock Grants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included from calculation of diluted net loss per share	4,648,526	7,482,032	1,305,421

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued compensation	$ 9,282	$ 4,102
Operating lease liabilities, current	2,354
Accrued in process research and development	1,600
Accrued consulting fees	1,337	665
Accrued other	1,126	769
Accrued legal fees	837	1,310
Accrued accounting fees	173	722
Total accrued expenses	$ 16,709	$ 7,568

Fair Value Measurements - Assets Measured at Fair Value on Recurring Basis (Details) - Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	$ 82,125	$ 17,295
U S Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	91,717
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	37,411
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	156,277
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis		123,439
Quoted Market Prices for Identical Assets (Level 1) \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	82,125	17,295
Quoted Market Prices for Identical Assets (Level 1) \| U S Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	91,717
Quoted Market Prices for Identical Assets (Level 1) \| U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis		$ 123,439
Significant Other Observable Inputs (Level 2) \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	37,411
Significant Other Observable Inputs (Level 2) \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	$ 156,277

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash Equivalents, at Carrying Value	$ 18.7
Prepaid Expenses and Other Current Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest receivable	$ 1.5	$ 0.5

Fair Value Measurements - Schedule of Available for sale Investments by Security Type (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale Investments, Amortized Cost	$ 266,465
Available-for-sale Investments, Gross Unrealized Gains	295
Available-for-sale Investments, Gross Unrealized Losses	(20)
Available-for-sale Investments, Total Fair Value	266,740
U S Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale Investments, Amortized Cost	77,993
Available-for-sale Investments, Gross Unrealized Gains	57
Available-for-sale Investments, Total Fair Value	78,050
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale Investments, Amortized Cost	32,413
Available-for-sale Investments, Total Fair Value	32,413
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale Investments, Amortized Cost	156,059
Available-for-sale Investments, Gross Unrealized Gains	238
Available-for-sale Investments, Gross Unrealized Losses	(20)
Available-for-sale Investments, Total Fair Value	$ 156,277

Fair Value Measurements - Schedule of Contractual Maturities of Available-for-sale Debt Securities (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Fair Value Disclosures [Abstract]
Due within one year	$ 237,449
One to two years	29,291
Total	$ 266,740

Long-Term Debt - Additional Information (Details) - Term Loan		12 Months Ended
	May 02, 2019 USD ($) Tranche	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 150,000,000
Amount funded	$ 30,000,000
Number of additional tranches \| Tranche	3
Remaining borrowing capacity	$ 120,000,000
Interest only payment period	36 months
Maturity date	May 01, 2024
Percentage of exit fee on amount borrowed on final repayment	1.75%
Percentage of exit fee on amount borrowed on partial prepayment	1.75%
Debt covenant minimum unrestricted cash percentage	25.00%
Minimum indebtedness amount		$ 2,500,000
Prepayment Occurs through First Anniversary of Closing Date
Debt Instrument [Line Items]
Percentage of prepayment fee	3.00%
First Anniversary of Closing Date through Second Anniversary of Closing Date
Debt Instrument [Line Items]
Percentage of prepayment fee	2.00%
Second Anniversary of Closing Date and Prior to May 1, 2024
Debt Instrument [Line Items]
Percentage of prepayment fee	1.00%
LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	6.15%
Interest rate	2.00%
Debt instrument, description of variable rate basis	Each term loan under the Credit Facility bears interest at an annual rate equal to the sum of (i) one-month LIBOR (customarily defined, with a change to prime rate if LIBOR funding becomes unlawful or impractical) plus (ii) 6.15%, subject to a LIBOR floor of 2.00%.
MidCap Financial Trust
Debt Instrument [Line Items]
Basis spread on variable rate		3.00%
Tranche One
Debt Instrument [Line Items]
Remaining borrowing capacity	$ 40,000,000
Tranche Two
Debt Instrument [Line Items]
Remaining borrowing capacity	30,000,000
Tranche Three
Debt Instrument [Line Items]
Remaining borrowing capacity	$ 50,000,000

Long-Term Debt - Schedule of Long-term Debt (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Debt Disclosure [Abstract]
Term loan	$ 30,000
Debt discount and issuance costs	(1,541)
Long-term debt	$ 28,459

Long-Term Debt - Schedule of Future Minimum Principal Payments (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Debt Disclosure [Abstract]
2020	$ 0
2021	5,833
2022	10,000
2023	10,000
2024	4,167
Total	$ 30,000

Convertible Notes Financing - Additional Information (Details) - Convertible Promissory Note - USD ($)	Jan. 04, 2018	Oct. 02, 2017
Debt Instrument [Line Items]
Amount of issued		$ 6,000,000
Interest rate		8.00%
Maturity date		Oct. 02, 2018
Amount to be raised by automatic conversion of the Note upon qualified equity financing		$ 40,000,000
Series A Convertible Preferred Stock
Debt Instrument [Line Items]
Number of shares issued for conversion of the Note	3,499,209

License and Asset Acquisitions - Additional Information (Details) - USD ($)						1 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 21, 2018	Jun. 24, 2018	Jan. 04, 2018	Oct. 02, 2017	May 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
In process research and development							$ 3,600,000	$ 49,659,000	$ 5,500,000
GB002
Business Acquisition [Line Items]
In process research and development									$ 5,500,000
GB001
Business Acquisition [Line Items]
In process research and development								19,148,000
GB004
Business Acquisition [Line Items]
In process research and development								20,000,000
GB1275
Business Acquisition [Line Items]
In process research and development							1,000,000	$ 7,501,000
Pulmokine, Inc. \| License Agreement \| GB002
Business Acquisition [Line Items]
Product license term					10 years
Upfront payment					$ 5,500,000
Milestones accrued					0
Pulmokine, Inc. \| License Agreement \| GB002 \| Maximum
Business Acquisition [Line Items]
Development and regulatory milestone payments, payable					63,000,000
Commercial milestone payments, payable					45,000,000
Sales milestone payments, payable					$ 190,000,000
AA Biopharma Inc. \| GB001
Business Acquisition [Line Items]
In process research and development				$ 19,300,000
AA Biopharma Inc. \| GB001 \| Common Stock
Business Acquisition [Line Items]
Business acquisition, aggregate number of shares issued				1,101,278
AA Biopharma Inc. \| GB001 \| Series Seed Convertible Preferred Stock
Business Acquisition [Line Items]
Business acquisition, aggregate number of shares issued				20,000,000
Aerpio Pharmaceuticals, Inc. \| License Agreement \| GB004
Business Acquisition [Line Items]
Milestones accrued	$ 0						0
Upfront payment, purchase consideration paid			$ 20,000,000
Aerpio Pharmaceuticals, Inc. \| License Agreement \| GB004 \| Maximum
Business Acquisition [Line Items]
Development and regulatory milestone payments, payable			55,000,000
Commercial milestone payments, payable			85,000,000
Sales milestone payments, payable			$ 260,000,000
Adhaere Pharmaceuticals, Inc. \| GB1275
Business Acquisition [Line Items]
Milestones accrued	0						$ 0
In process research and development	$ 7,500,000
Upfront payment, purchase consideration paid		$ 7,500,000
Milestones payment						$ 1,000,000
Adhaere Pharmaceuticals, Inc. \| GB1275 \| Maximum
Business Acquisition [Line Items]
Regulatory, development and sales milestone payments payable		$ 62,000,000

License and Asset Acquisitions - Schedule of IPR&D Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development	$ 3,600	$ 49,659	$ 5,500
GB002
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development			$ 5,500
GB001
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development		19,148
GB004
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development		20,000
GB1275
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development	1,000	7,501
Other Programs
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development	$ 2,600	$ 3,010

Income Taxes - Schedule of Amount of Net Loss Before Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. loss before taxes	$ 138,342	$ 116,920	$ 6,771
Foreign loss before taxes	41,965	30,049
Loss before income taxes	$ 180,307	$ 146,969	$ 6,771

Income Taxes - Schedule of Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal	$ 0	$ 0	$ 0
State	0	0	0
Foreign	0	0	0
Total current income tax expense	0	0	0
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	0	0	0
Total deferred income tax expense	0	0	0
Total income tax expense	$ 0	$ 0	$ 0

Income Taxes - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance	$ 41.0
Federal research and development credits expiration year start	2038
Decrease in deferred tax asset	$ 0.8
Unrecognized tax benefits that would not impact effective tax rate	2.6
Orphan Drug Credit
Operating Loss Carryforwards [Line Items]
Research and development credit	$ 9.6
Maximum
Operating Loss Carryforwards [Line Items]
Net operating losses carryforward available to offset future federal taxable income , percentage	80.00%
Federal
Operating Loss Carryforwards [Line Items]
Net operating losses (“NOL”) carryforwards	$ 175.8
Net operating loss carry forwards expiration year start	2034
Net operating losses (“NOL”) that can be carried forward indefinitely	$ 172.9
Research and development credit	9.6
California
Operating Loss Carryforwards [Line Items]
Net operating losses (“NOL”) carryforwards	$ 1.1
Net operating loss carry forwards expiration year start	2036
Research and development credit	$ 2.7
Irish
Operating Loss Carryforwards [Line Items]
Net operating losses (“NOL”) carryforwards	$ 53.0

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating losses	$ 43,626	$ 14,442	$ 306
Tax credits, net	9,196	1,131
Amortization	6,597	6,267	1,588
Lease liability	2,329
Accrued compensation	1,476	834
Stock-based compensation	1,388		1
Other	383	154
Total gross deferred tax assets	64,995	22,828	1,895
Deferred tax liabilities:
Right of use asset	(2,164)
Property, plant and equipment	(57)	(16)
Stock-based compensation		(1,057)
Total gross deferred tax liabilities	(2,221)	(1,073)
Valuation allowance	$ (62,774)	$ (21,755)	$ (1,895)

Income Taxes - Reconciliation of Federal Statutory Income Tax Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%	34.00%
State income taxes, net of federal benefit			5.73%
Change in valuation allowance	(22.12%)	(13.17%)	(27.97%)
Change in tax law			(11.85%)
Research and experimentation credits	3.81%	0.77%
Foreign rate differential	(1.84%)	(1.74%)
Stock-based compensation		(2.60%)
In process research and development		(3.92%)
Other	(0.85%)	(0.34%)	0.09%

Income Taxes - Schedule of Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits, Excluding Interest and Penalties (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Beginning Balance	$ 408
Increase related to current year positions	2,346	$ 408
Ending Balance	$ 2,754	$ 408

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($)							1 Months Ended			12 Months Ended
	Feb. 12, 2019	Sep. 06, 2018	Jul. 20, 2018	May 21, 2018	Jan. 04, 2018	Dec. 03, 2015	Mar. 31, 2018	Jan. 31, 2018	Nov. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders Equity Deficit [Line Items]
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs										$ 291,311,000
Common stock, voting right										one
Shares of common stock, repurchase										4,648,526	7,482,032	1,305,421
Founder
Stockholders Equity Deficit [Line Items]
Issuance price per share		$ 9.63		$ 2.61
Sale of shares of common stock		1,795,023		251,547
Percentage of fully diluted share capital										15.00%
Increased in equity capital amount										$ 300,000,000
Additional shares of restricted stock subject to vesting restrictions		1,795,023		251,547
Common Stock
Stockholders Equity Deficit [Line Items]
Sale of shares of common stock										19,837,500
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs										$ 2,000
Unrestricted shares of common stock were subject to service vesting conditions											4,580,444
Founder Shares
Stockholders Equity Deficit [Line Items]
Issuance price per share						$ 0.0001
Sale of shares of common stock						9,160,888
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs						$ 4,100
Common Stock vesting percentage					50.00%
Common stock vesting period					5 years
Common Stock \| Stock Restriction Agreements
Stockholders Equity Deficit [Line Items]
Unrestricted shares of common stock were subject to service vesting conditions								4,580,444
Initial Public Offering ("IPO")
Stockholders Equity Deficit [Line Items]
Sale of shares of common stock	19,837,500
Series Seed Convertible Preferred Stock \| Initial Public Offering ("IPO") \| Common Stock
Stockholders Equity Deficit [Line Items]
Conversion of preferred stock into common stock										30,493,460
Series Seed Convertible Preferred Stock \| AA Biopharma Inc.
Stockholders Equity Deficit [Line Items]
Convertible Preferred Stock Issued					20,000,000
Preferred Stock, Conversion Basis					On January 4, 2018, the Company issued an aggregate of 20,000,000 shares of Series Seed Convertible Preferred Stock in connection with the merger agreement with AA Biopharma Inc.
Shares Issuable upon Conversion of Series A Convertible Preferred Stock
Stockholders Equity Deficit [Line Items]
Convertible Preferred Stock Issued							45,714,286	45,714,286
Issuance price per share							$ 1.75	$ 1.75
Preferred stock, gross proceeds							$ 73,900,000	$ 73,900,000
Conversion of principal amount into preferred stock							$ 6,100,000	$ 6,100,000
Shares Issuable upon Conversion of Series A Convertible Preferred Stock \| Initial Public Offering ("IPO") \| Common Stock
Stockholders Equity Deficit [Line Items]
Conversion of preferred stock into common stock										30,493,460
Series B Convertible Preferred Stock
Stockholders Equity Deficit [Line Items]
Convertible Preferred Stock Issued			71,506,513
Issuance price per share			$ 3.2167
Proceeds from issuance of convertible preferred stock, net			$ 230,000,000
Shares Issuable upon Conversion of Series B Convertible Preferred Stock \| Initial Public Offering ("IPO") \| Common Stock
Stockholders Equity Deficit [Line Items]
Conversion of preferred stock into common stock										30,493,460
Series A Convertible Preferred Stock
Stockholders Equity Deficit [Line Items]
Convertible Preferred Stock Issued											42,215,077
Proceeds from issuance of convertible preferred stock, net											$ 73,491,000
Series A Convertible Preferred Stock \| Stock Restriction Agreements
Stockholders Equity Deficit [Line Items]
Shares subject to forfeiture									1,305,421

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Feb. 06, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares outstanding awarded		8,538,060	5,107,329
Stock options granted during period		4,194,624	5,143,551	0
Stock options exercised during the year		419,593
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average period of cost expects to recognize		2 years 9 months 18 days
Unrecognized compensation costs		$ 13.5
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield		0.00%	0.00%
Weighted-average grant date fair value per share		$ 13.17	$ 4.87
Aggregate fair value of stock options vested during period		$ 7.2	$ 0.1
Aggregate intrinsic value of stock options exercised during period		6.9
Unrecognized compensation costs		$ 61.0
Weighted-average period of cost expects to recognize		2 years 10 months 24 days
Stock options exercised during the year			0
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of share reserved for future issuance	5,750,000
Term of awards	10 years
Percentage of amount increase in outstanding shares	5.00%
Common stock available for issuance		1,751,485
Shares outstanding awarded		4,003,040
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of share reserved for future issuance	700,000	700,000
Term of awards	10 years
Percentage of amount increase in outstanding shares	1.00%
2019 Employee Stock Purchase Plan \| Stock-Based Compensation Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs		$ 1.3
Weighted-average period of cost expects to recognize		1 year 1 month 6 days
2019 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase of common stock through payroll deductions, percentage	20.00%
2017 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares outstanding awarded		4,535,020
2017 Equity Incentive Plan \| Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted stock awards, Unvested		561,868

Equity Incentive Plans - Schedule of Fair Value Assumptions Stock Options (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.38%	2.65%
Risk-free interest rate, maximum	2.58%	2.96%
Volatility, minimum	70.25%	69.13%
Volatility, maximum	86.92%	77.62%
Dividend yield	0.00%	0.00%
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.46%
Risk-free interest rate, maximum	1.87%
Volatility, minimum	72.08%
Volatility, maximum	78.70%
Dividend yield	0.00%
Minimum [Member] \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected life (in years)	4 years 7 months 6 days	5 years 3 months 18 days
Minimum [Member] \| ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected life (in years)	5 months 26 days
Maximum \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected life (in years)	6 years 1 month 6 days	6 years 1 month 6 days
Maximum \| ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected life (in years)	1 year 11 months 26 days

Equity Incentive Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Subject to Options Outstanding, Beginning	5,107,329
Shares Subject to Options Outstanding, Options granted	4,194,624	5,143,551	0
Shares Subject to Options Outstanding, Option exercised	(419,593)
Shares Subject to Options Outstanding, Options forfeited/cancelled	(344,300)	(36,222)
Shares Subject to Options Outstanding, Ending	8,538,060	5,107,329
Shares Subject to Options Outstanding, Options vested and exercisable as of December 31,2019	1,215,471
Weighted-Average Exercise Price, Outstanding, beginning	$ 7.51
Weighted-Average Exercise Price, Options granted	20.11	$ 7.49
Weighted-Average Exercise Price, Option exercised	4.87
Weighted-Average Exercise Price, Options forfeited/cancelled	11.64	4.85
Weighted-Average Exercise Price, Outstanding, ending	13.67	$ 7.51
Weighted-Average Exercise Price, Options vested and exercisable as of December 31, 2019	$ 7.25
Weighted-Average Remaining Contractual Life (Years), Outstanding	9 years	9 years 8 months 12 days	0 years
Weighted-Average Remaining Contractual Life (Years), Options vested and exercisable	8 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 35,385	$ 16,343
Aggregate Intrinsic Value, Options vested and exercisable	$ 10,183

Equity Incentive Plans - Summary of Restricted Stock Activity (Details) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Restricted Stock Units Outstanding, Nonvested, beginning	7,482,032	1,305,421
Number of Restricted Stock Units Outstanding, Granted	0	8,673,584	1,305,421
Number of Restricted Stock Units Outstanding, Vested	(2,833,506)	(2,369,696)
Number of Restricted Stock Units Outstanding, Forfeited		(127,277)
Number of Restricted Stock Units Outstanding, Nonvested, ending	4,648,526	7,482,032	1,305,421
Weighted-Average Grant Date Fair Value, Nonvested	$ 4.01	$ 0.09
Weighted-Average Grant Date Fair Value, Granted		5.53	$ 0.09
Weighted-Average Grant Date Fair Value, Vested	4.05	7.58
Weighted-Average Grant Date Fair Value, Forfeited		0.09
Weighted-Average Grant Date Fair Value, Nonvested	$ 3.98	$ 4.01	$ 0.09

Equity Incentive Plans - Stock-Based Compensation Expense Reported in Condensed Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 20,819	$ 30,947	$ 32
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	10,227	679	17
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 10,592	$ 30,268	$ 15

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 6,639	$ 3,490
Less: accumulated depreciation	1,214	297
Property and equipment, net	5,425	3,193
Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 1,097	918
Office Equipment \| Minimum
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	3 years
Office Equipment \| Maximum
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	7 years
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	5 years
Total property and equipment	$ 124	15
Software
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	3 years
Total property and equipment	$ 87	50
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 3,054	1,070
Lab Equipment \| Minimum
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	2 years
Lab Equipment \| Maximum
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	5 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	$ 2,229	1,243
Leasehold Improvements \| Minimum
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	6 years
Leasehold Improvements \| Maximum
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	7 years
Construction in Process
Property Plant And Equipment [Line Items]
Total property and equipment	$ 48	$ 194

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 0.9	$ 0.3	$ 0.0

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Lessee Lease Description [Line Items]
Non-cancelable operating sublease, expiration date for initial leased space		2025-01
Non-cancelable operating sublease, expiration date for expansion space leased		2022-12
Lessee, Operating Sublease, Existence of Option to Extend [true false]		true
Lessee, operating sublease, option to extend		options to extend for the entire premises through October 2028
Operating sublease, annual increase percentage for base rent		3.00%
Monthly base rent for permanent space	$ 63,425
Monthly base rent for temporary space	$ 28,745
Option to extend lease term of permanent space	12 months
Annual increase percentage for lease charges	3.00%
Weighted average discount rate, operating leases		7.00%
Weighted average remaining lease term		4 years
Cash paid for operating lease liabilities		$ 3,000,000
Rent expense		$ 3,100,000	$ 1,500,000	$ 0
San Diego, California
Lessee Lease Description [Line Items]
Lease commencement date for permanent space	May 01, 2020
Lease expiration date for permanent space	Dec. 31, 2021
Lease commencement date for temporary space	Jan. 01, 2020

Commitments and Contingencies - Schedule of Lease Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 3,011
Short-term lease cost	133
Total lease cost	$ 3,144

Commitments and Contingencies - Schedule of Gross Future Minimum Annual Rental Commitments (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Leases [Abstract]
2020	$ 3,038
2021	3,127
2022	3,220
2023	1,694
2024	1,745
Total undiscounted rent payments	12,824
Present value discount	(1,733)
Present value	11,091
Current portion of operating lease liabilities (included as a component of accrued expenses and other current liabilities)	2,354
Noncurrent operating lease liabilities	8,737
Total operating lease liability	$ 11,091

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-Cancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Leases [Abstract]
2019	$ 2,944
2020	3,035
2021	3,123
2022	3,216
2023	1,690
Thereafter	1,741
Total	$ 15,749

Selected Quarterly Financial Information (Unaudited) - Schedule of Selected Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Loss from operations	$ (55,787)	$ (49,986)	$ (46,349)	$ (34,017)	$ (39,807)	$ (50,024)	$ (33,036)	$ (26,126)	$ (186,139)	$ (148,993)	$ (6,653)
Net loss	$ (54,698)	$ (48,500)	$ (44,498)	$ (32,611)	$ (38,794)	$ (49,409)	$ (32,729)	$ (26,037)	$ (180,307)	$ (146,969)	$ (6,771)
Per common share:
Net loss per share, basic and diluted	$ (0.89)	$ (0.80)	$ (0.74)	$ (0.90)	$ (4.92)	$ (8.03)	$ (5.52)	$ (4.31)	$ (3.29)	$ (22.59)	$ (0.74)

- Definition

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

+ References + Details