Krystal Biotech (KRYS) 10-K 1 Mar 21 2020 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 19, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-38210
Entity Registrant Name	Krystal Biotech, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-1080209
Entity Address, Address Line One	2100 Wharton Street
Entity Address, Address Line Two	Suite 701
Entity Address, City or Town	Pittsburgh
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15203
City Area Code	412
Local Phone Number	586-5830
Title of 12(b) Security	Common Stock
Trading Symbol	KRYS
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 595.4
Entity Common Stock, Shares Outstanding		22,194,752
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement relating to its 2021 Annual Meeting of Stockholders are incorporated by reference into Part III of this Report where indicated. Such proxy statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Entity Central Index Key	0001711279
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 268,269	$ 187,514
Short-term investments	2,993	6,171
Prepaid and other current assets	3,796	2,195
Total current assets	275,058	195,880
Property and equipment, net	30,876	8,475
Long-term investments	0	497
Right-of-use assets	3,298	2,709
Other non-current assets	1,612	1,462
Total assets	310,844	209,023
Current liabilities
Accounts payable	2,105	1,021
Current portion of lease liability	638	480
Accrued expenses and other current liabilities	5,109	1,826
Build-to-suit lease liability	7,600	0
Total current liabilities	15,452	3,327
Lease liability	3,308	2,782
Total liabilities	18,760	6,109
Commitments and contingencies (Note 6)
Stockholders' equity
Preferred stock; $0.00001 par value; 20,000,000 shares authorized at    December 31, 2020 and 2019; 2,061,773 shares issued, and no    shares outstanding at December 31, 2020 and 2019	0	0
Common stock; $0.00001 par value; 80,000,000 shares authorized at    December 31, 2020 and 2019; 19,714,220 and 17,354,310 shares   issued and outstanding at December 31, 2020 and 2019, respectively	0	0
Additional paid-in capital	363,292	241,951
Accumulated other comprehensive income	6	10
Accumulated deficit	(71,214)	(39,047)
Total stockholders' equity	292,084	202,914
Total liabilities and stockholders' equity	$ 310,844	$ 209,023

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Convertible preferred stock, par value (in usd per share)	$ 0.00001	$ 0.00001
Convertible preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Convertible preferred stock, shares issued (in shares)	2,061,773	2,061,773
Convertible preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized (in shares)	80,000,000	80,000,000
Common stock, shares issued (in shares)	19,714,220	17,354,310
Common stock, shares outstanding (in shares)	19,714,220	17,354,310

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Expenses
Research and development	$ 17,936	$ 15,616
General and administrative	15,063	6,465
Total operating expenses	32,999	22,081
Loss from operations	(32,999)	(22,081)
Other Income
Interest and other income, net	832	2,993
Net loss	(32,167)	(19,088)
Unrealized gain (loss) on available-for-sale securities	(4)	8
Comprehensive loss	$ (32,171)	$ (19,080)
Earnings Per Share, Basic and Diluted [Abstract]
Net loss per common share: Basic and diluted (in usd per share)	$ (1.71)	$ (1.20)
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Weighted-average common shares outstanding: Basic and diluted (in shares)	18,787,161	15,901,083

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 113,226		$ 133,183	$ 2	$ (19,959)
Beginning balance (in shares) at Dec. 31, 2018		14,428,916
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net	107,529		107,529
Issuance of common stock, net (in shares)		2,925,394
Stock-based compensation expense	1,239		1,239
Unrealized gain (loss) on available-for-sale securities	8			8
Net loss	(19,088)				(19,088)
Ending balance at Dec. 31, 2019	202,914		241,951	10	(39,047)
Ending balance (in shares) at Dec. 31, 2019		17,354,310
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net	118,035		118,035
Issuance of common stock, net (in shares)		2,359,910
Stock-based compensation expense	3,306		3,306
Unrealized gain (loss) on available-for-sale securities	(4)			(4)
Net loss	(32,167)				(32,167)
Ending balance at Dec. 31, 2020	$ 292,084		$ 363,292	$ 6	$ (71,214)
Ending balance (in shares) at Dec. 31, 2020		19,714,220

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating Activities
Net loss	$ (32,167)	$ (19,088)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	1,851	1,090
Stock-based compensation expense	3,272	1,239
Loss on disposal of fixed assets	33	67
Changes in operating assets and liabilities
Prepaid expenses and other current assets	(1,911)	(868)
Other non-current assets	(934)	(1,362)
Lease liability	685	(116)
Accounts payable	783	(199)
Accrued expenses and other current liabilities	2,305	547
Net cash used in operating activities	(26,083)	(18,690)
Investing Activities
Purchases of property and equipment	(14,843)	(6,399)
Purchases of short-term investments	(3,205)	(8,596)
Proceeds from maturities of short-term investments	6,867	10,501
Purchases of long-term investments	0	(497)
Net cash used in investing activities	(11,181)	(4,991)
Financing Activities
Issuance of common stock, net	118,019	107,525
Net cash provided by financing activities	118,019	107,525
Net increase in cash and cash equivalents	80,755	83,844
Cash and cash equivalents at beginning of year	187,514	103,670
Cash and cash equivalents at end of year	268,269	187,514
Supplemental Disclosures of Non-Cash Investing and Financing Activities
Unpaid purchases of property and equipment	9,697	681
Initial recognition of right-of-use assets	911	3,066
Unpaid offering costs	$ 131	$ 0

Organization

Organization	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Organization	Organization Krystal Biotech, Inc. (the “Company,” or “we” or other similar pronouns) commenced operations on April 15, 2016. On March 31, 2017, the Company converted from a California limited liability company to a Delaware C-corporation, and changed its name from Krystal Biotech LLC to Krystal Biotech, Inc. On June 19, 2018, the Company incorporated Krystal Australia Pty Ltd., an Australian proprietary limited company, for the purpose of undertaking preclinical and clinical studies in Australia. On April 24, 2019, the Company incorporated Jeune, Inc. in Delaware, a wholly-owned subsidiary, for the purpose of undertaking preclinical and clinical studies for aesthetic skin conditions. We are a clinical stage biotechnology company leading the field of redosable gene therapy for the treatment serious rare diseases. Using our patented platform that is based on engineered HSV-1, we create vectors that efficiently deliver therapeutic transgenes to cells of interest in multiple organ systems. The cell’s own machinery then transcribes and translates the encoded effector to treat or prevent disease. We formulate our vectors for non-invasive or minimally invasive routes of administration at a doctor’s office or potentially in the patient’s home. Our goal is to develop easy to use, redosable gene therapies to dramatically improve the lives of patients living with rare diseases. Our innovative technology platform is supported by in-house, commercial scale cGMP manufacturing capabilities. Liquidity As of December 31, 2020, the Company had an accumulated deficit of $71.2 million. With the net proceeds raised from its public and private securities offerings, including the public offering completed on May 21, 2020, the Company believes that its cash, cash equivalents and short-term investments of approximately $271.3 million as of December 31, 2020 will be sufficient to allow the Company to fund its planned operations for at least the next 12 months from the date of this Annual Report on Form 10-K. As the Company continues to incur losses, a transition to profitability is dependent upon the successful development, approval and commercialization of its product candidates and the achievement of a level of revenues adequate to support the Company’s cost structure. The Company may never achieve profitability, and unless and until it does the Company will continue to need to raise additional capital or obtain financing from other sources. Management intends to fund future operations through the sale of equity and debt financings and may also seek additional capital through arrangements with strategic partners or other sources. There can be no assurance that additional funding will be available on terms acceptable to the Company, if at all. The Company is subject to risks common to companies in the biotechnology industry, including but not limited to the failure of product candidates in clinical and preclinical studies, the development of competing product candidates or other technological innovations by competitors, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to commercialize product candidates.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) as found in the Accounting Standards Codification (“ASC”), the Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”) and the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”). All intercompany balances and transactions have been eliminated in consolidation. Certain prior period amounts have been reclassed to conform to the current period presentation. The reclassified amounts have no impact to the Company's previously reported financial position or results of operation. Risks and Uncertainties The pandemic caused by an outbreak of a new strain of coronavirus (“COVID-19”) has resulted, and is likely to continue to result, in significant national and global economic disruption and may adversely affect our business. The Company is actively monitoring the impact of COVID-19 and the possible effects on its financial condition, liquidity, operations, suppliers, industry, and workforce. However, the full extent, consequences, and duration of the COVID-19 pandemic and the resulting impact on the Company cannot currently be predicted. The Company will continue to evaluate the impact that these events could have on the operations, financial position, and the results of operations and cash flows during fiscal year 2021. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts in the consolidated financial statements and accompanying notes. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements. Estimates are used in the following areas, including: stock-based compensation expense, accrued expenses, the fair value of financial instruments, the incremental borrowing rate for lease liabilities, construction in progress, and the valuation allowance included in the deferred income tax calculation. Segment and Geographical Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company and the Company’s chief operating decision maker view the Company’s operations and manage its business in one operating segment, which is the business of developing and commercializing pharmaceuticals. Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to credit risk consist of cash, cash equivalents and investments. The Company’s policy is to invest its cash, cash equivalents and investments in money market funds, certificates of deposit, U.S. Treasury bills, and various other bank deposit accounts. The counterparties to the agreements relating to the Company’s investments consist of financial institutions of high credit standing. The Company is exposed to credit risk in the event of default by the financial institutions to the extent amounts recorded on the balance sheets are in excess of insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss. Cash, Cash Equivalents and Investments Cash and cash equivalents consist of money market funds and bank deposits. Cash equivalents are defined as short-term, highly liquid investments with original maturities of 90 days or less at the date of purchase. Investments with maturities of greater than 90 days but less than one year are classified as short-term investments on the consolidated balance sheets and consist of U.S. Treasury bills and certificates of deposit. Investments with maturities of greater than one year are classified as long-term investments on the consolidated balance sheets and consist of certificates of deposit. Accrued interest on U.S. Treasury bills and certificates of deposit are also classified as short-term investments. As our entire investment portfolio is considered available for use in current operations, we classify all investments as available-for-sale securities. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive loss, which is a separate component of stockholders’ equity in the consolidated balance sheets. Fair Value of Financial Instruments Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. There is a three-level hierarchy that prioritizes the inputs used in determining fair value by their reliability and preferred use, as follows: • Level 1 —Valuations based on quoted prices in active markets for identical assets or liabilities. • Level 2 —Valuations based on quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets and liabilities in inactive markets, or other inputs that are observable, or can be corroborated by observable market data. • Level 3 —Valuations based on inputs that are both significant to the fair value measurement and unobservable. To the extent that a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized within Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. There have been no significant changes to the valuation methods utilized by the Company during the periods presented. There have been no transfers between Level 1, Level 2, and Level 3 in any periods presented. The carrying amounts of financial instruments consisting of cash and cash equivalents, investments, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities included in the Company’s financial statements, are reasonable estimates of fair value, primarily due to their short maturities. Marketable securities are classified as long-term investments if the Company has the ability and intent to hold them and such holding period is longer than one year. The Company classifies all of its investments as available-for-sale. Our available-for-sale, short-term investments, which consist of U.S. Treasury bills and certificates of deposit, are considered to be Level 2 valuations. The fair value of Level 2 financial assets is determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. Property and Equipment, net Property and equipment, net, is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred, while costs of major additions and betterments are capitalized. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Computer equipment and software 3 years Lab equipment 3 - 7 years Furniture and fixtures 3 years Leasehold improvement shorter of 8 years or remaining life of lease Construction-in-progress is not depreciated until the asset is placed in service. Impairment of Long-Lived Assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. An impairment loss would be recognized when estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount of the asset. The Company has not recognized any impairment losses for the years ended December 31, 2020 and 2019. Leases We have entered into lease agreements for our laboratory, manufacturing and office spaces. On January 1, 2019, we adopted FASB ASC Topic 842, Leases ("ASC 842"). Pursuant to ASC 842, all of our leases outstanding on January 1, 2019 continued to be classified as operating leases. With the adoption of ASC 842, we recorded an operating lease right-of-use asset of $1.1 million and an operating lease liability of $1.4 million on the consolidated balance sheet. Right-of-use lease assets represent our right to use the underlying asset during the lease term and the lease obligations represent our commitment to make lease payments arising from the lease. Right-of-use lease assets and obligations were recognized based on the present value of remaining lease payments over the lease term. As the Company’s lease agreements do not provide an implicit rate and as the Company does not have any external borrowings, we have used an estimated incremental borrowing rate based on the information available at lease commencement in determining the present value of lease payments. The incremental borrowing rate is the rate of interest that the Company would expect to borrow on a collateralized and fully amortizing basis over a similar term an amount equal to the lease payments in a similar economic environment. Operating lease expense is recognized on a straight-line basis over the lease term. Variable lease expense is recognized in the period in which the obligation for the payment is incurred. The Company adopted the new leasing standard as of the effective date of January 1, 2019, with no restatement of prior periods or cumulative adjustment to retained earnings. Upon adoption, the Company took advantage of the transition package of practical expedients permitted within ASC 842, which allowed the Company not to reassess previous accounting conclusions around whether arrangements were, or contained, leases, as well as to carry forward both the historical classification of leases and the treatment of initial direct costs for existing leases. In addition, the Company also has made an accounting policy election to exclude leases with an initial term of twelve months or less from its balance sheet and to account for the lease and non-lease components of its operating leases as a single component. For lease arrangements where it has been determined that the Company has control over an asset that is under construction and is thus considered the accounting owner of the asset during the construction period, the Company records a construction-in-progress asset ("CIP") and corresponding financial obligation on the consolidated balance sheet. Once the construction is complete, an assessment will be performed to determine whether the lease meets certain "sale-leaseback" criteria. If the sale-leaseback criteria are determined to be met, the Company will remove the asset and related financial obligation from the balance sheet and treat the building lease as either an operating or finance lease based on our assessment of the guidance. If, upon completion of construction, the project does not meet the "sale-leaseback" criteria, the lease will be treated as a financing obligation and the Company will depreciate the asset over its estimated useful life for financial reporting purposes. Research and Development Expenses Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, facilities and overhead, preclinical and clinical activities, related clinical manufacturing costs, contract management services, regulatory and other related costs. The Company estimates contract research and clinical trials materials manufacturing expenses based on the services performed pursuant to contracts with research and manufacturing organizations that manufacture materials used in the Company’s ongoing preclinical and clinical studies. Non-refundable advanced payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. These estimates are based on communications with third party service providers and the Company’s estimates of accrued expenses using information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. Stock-Based Compensation Expense The Company accounts for its stock-based compensation awards in accordance with FASB ASC Topic 718, Compensation-Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments, including grants of stock options and restricted stock, to be recognized in the statements of operations based on their grant-date fair values. Compensation expense is recognized on a straight-line basis based on the grant-date fair value over the associated service period of the award, which is generally the vesting term. The Company estimates the fair value of its stock options using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including: (i) the expected stock price volatility; (ii) the expected term of the award; (iii) the risk-free interest rate; and (iv) expected dividends. Due to the lack of sufficient history and trading volume of our common stock and a lack of Company-specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected term of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Due to the lack of Company-specific historical option activity, the Company has estimated the expected term of its employee stock options using the “simplified” method, whereby the expected term equals the arithmetic mean of the vesting term and the original contractual term of the option. The risk-free interest rates are based on U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid and does not expect to pay dividends in the foreseeable future. The Company is also required to estimate forfeitures at the time of grant and to revise those estimates in subsequent periods if actual forfeitures differ from its estimates. To the extent that actual forfeitures differ from the Company’s estimates, the differences are recorded as a cumulative adjustment in the period the estimates were revised. Income Taxes Income taxes are recorded in accordance with FASB ASC Topic 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. Under this method, we record deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect when the differences are expected to reverse. Valuation allowances are provided when necessary to reduce net deferred tax assets to the amount that is more likely than not to be realized. Based on the available evidence, we are unable, at this time, to support the determination that it is more likely than not that our deferred tax assets will be utilized in the future. Accordingly, we recorded a full valuation allowance as of December 31, 2020. We intend to maintain a valuation allowance until sufficient evidence exists to support its reversal. 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 will more likely than not be realized. 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. As of December 31, 2020, the Company did not have any significant uncertain tax positions. The Company may recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2020 and 2019, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations and comprehensive loss. Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions from non-owner sources. Unrealized gains or losses on available-for-sale securities is a component of other comprehensive gains or losses and is presented net of taxes. We have not recorded any reclassifications from other comprehensive gains or losses to net loss during any period presented. Recent Accounting Pronouncements ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU 2018-13 - Fair Value Measurement (Topic 820) (“ASU 2018-13”) which removes, modifies and adds disclosure requirements on fair value measurements. ASU 2018-13 removes disclosure requirements for transfers between Level 1 and Level 2 measurements and valuation processes for Level 3 measurements but adds new disclosure requirements including changes in unrealized gains/losses in other comprehensive income related to recurring Level 3 measurements. The amended guidance was effective for the Company in the first quarter of 2020. Certain aspects may be applied prospectively while other aspects may be applied retrospectively upon the effective date. The adoption of the guidance resulted in us disclosing the Company's cash, cash equivalents and available-for-sale securities by significant investment category as of December 31, 2020 and 2019.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common StockholdersBasic net loss per share attributable to common stockholders is calculated by dividing net loss attributable to common stockholders by the weighted average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss by the weighted-average number of shares of common stock and common share equivalents outstanding for the period. Stock options are common share equivalents. There were 853,614 and 420,766 common share equivalents outstanding as of December 31, 2020 and 2019, respectively, in the form of stock options, that have been excluded from the calculation of diluted net loss per common share as their effect would be anti-dilutive for all periods presented. (In thousands, except share and per share data) Year Ended December 31, 2020 2019 Numerator: Net loss per common share $ (32,167) $ (19,088) Denominator: Weighted-average basic and diluted common shares 18,787,161 15,901,083 Basic and diluted net loss per common share $ (1.71) $ (1.20) In January and February 2021, 2,474,038 additional shares were issued of our common stock in offerings subsequent to the balance sheet date. Including these shares will have a material effect on the diluted net loss per common share in future periods. Refer to Note 11 for discussion over these transactions.

Fair Value Instruments

Fair Value Instruments	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Instruments	Fair Value Instruments The following tables show the Company’s cash, cash equivalents and available-for-sale securities by significant investment category as of December 31, 2020 and 2019, respectively (in thousands): December 31, 2020 Amortized Cost Gross Gross Aggregate Fair Cash and Cash Short-term Marketable Securities (1) Long-term Marketable Securities (2) Level 1: Cash $ 9,463 — — $ 9,463 $ 9,463 — — Money market instruments 258,806 — — 258,806 258,806 — — Subtotal 268,269 — — 268,269 268,269 — — Level 2: U.S. treasury bills — — — — — — — Certificates of deposit 2,986 7 — 2,993 — 2,993 — Subtotal 2,986 7 — 2,993 — 2,993 — Total $ 271,255 $ 7 $ — $ 271,262 $ 268,269 $ 2,993 $ — December 31, 2019 Amortized Cost Gross Gross Aggregate Fair Cash and Cash Short-term Marketable Securities (1) Long-term Marketable Securities (2) Level 1: Cash $ 3 — — $ 3 $ 3 — — Money market instruments 187,511 — — 187,511 187,511 — — Subtotal 187,514 — — 187,514 187,514 — — Level 2: U.S. treasury bills 1,747 6 — 1,753 — 1,753 — Certificates of deposit 4,911 4 — 4,915 — 4,418 497 Subtotal 6,658 10 — 6,668 — 6,171 497 Total $ 194,172 $ 10 $ — $ 194,182 $ 187,514 $ 6,171 $ 497 (1) The Company’s short-term marketable securities mature in one year or less. (2) The Company’s long-term marketable securities mature between one year and two years. See Note 2 to these consolidated financial statements for additional discussion regarding the Company’s fair value measurements.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2020
Balance Sheet Components [Abstract]
Balance Sheet Components	Balance Sheet Components Property and Equipment, Net Property and equipment, net consist of the following (in thousands): December 31, December 31, Construction-in-progress $ 23,031 $ 2,431 Leasehold improvements 4,631 3,179 Furniture and fixtures 870 99 Computer equipment and software 82 45 Laboratory equipment 4,630 3,571 Total property and equipment 33,244 9,325 Accumulated depreciation and amortization (2,368) (850) Property and equipment, net $ 30,876 $ 8,475 Depreciation expense was $1.5 million and $748 thousand for the years ended December 31, 2020 and 2019, respectively. Refer to Note 6 for further discussion over construction-in-progress. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, December 31, Accrued preclinical and clinical expenses $ 1,735 $ 977 Accrued professional fees 642 24 Accrued payroll and benefits 1,486 510 Accrued taxes 40 40 Accrued construction in progress 1,049 263 Other current liabilities 26 12 Accrued financing fees 131 — Total $ 5,109 $ 1,826

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Significant Contracts and Agreements Lease Agreements On May 26, 2016, the Company signed an operating lease for laboratory and office space that commenced in June 2016 and expired on October 31, 2017 (the “2016 Lease”). The 2016 Lease was amended to increase the area leased to approximately 29,000 square feet and to extend the expiration date to February 28, 2027, including 3,800 square feet relating to a month-to-month lease that we utilized through February 2020. This lease includes our 7,500 square foot commercial scale cGMP-compliant manufacturing facility, ANCORIS. On December 26, 2019, we entered into a lease agreement for our second commercial gene therapy facility ("ASTRA") in the Pittsburgh, Pennsylvania area ("ASTRA lease") with Northfield I, LLC (the "Landlord" or "Northfield"). The 150,000 square foot facility is under construction and is expected to be completed and validated in 2022. The lease will commence when the space is delivered by Landlord as substantially complete and available for access, which is anticipated to be in 1H 2021, and has an initial term that expires on October 31, 2035. The ASTRA lease contains an option ("Purchase Option") to purchase the building, related improvements and take corresponding assignment of the Landlord's rights under its existing Ground Lease (the "Ground Lease"). The Purchase Option may be exercised by the Company at any time prior to the date that is ten days after the initial delivery date, as defined in the lease as the date in which certain delivery conditions have been met by the Landlord. A cash contribution in the amount of $2.4 million was paid to escrow on January 21, 2020. The contribution was intended to reduce the amount of the building construction costs and had the effect of reducing the base rental rate of the lease and as such, was recorded as prepaid rent in the consolidated balance sheet at time of payment. On October 5, 2020, the Company was provided with notice that the initial delivery conditions of the building had been met, including completion of the building shell, interior slab, and exterior doors, and on October 15, 2020, the Company gave the Landlord notice of its intent to purchase ASTRA for approximately $9.4 million, subject to the parties entering into a commercially reasonable purchase and sale agreement. The purchase is anticipated to close in 1H 2021 after substantial completion has been reached and the lease commences. As a result of the Company's ability to exercise its option to purchase ASTRA, the Company obtained control over the construction in progress of ASTRA as of October 5, 2020. The Company recorded a $10 million CIP asset and a corresponding build-to-suit lease liability related to the costs incurred by the Landlord, offset by the previous cash contribution of $2.4 million. Upon completion of the construction, the Company does not expect to qualify for sale-leaseback accounting due to the outstanding purchase option. Under the existing lease agreement, the Company previously provided a $1.5 million deposit to the Landlord and intends to apply this deposit as a credit against the purchase price at closing. The Company also became the accounting owner of the Ground Lease due to obtaining control over ASTRA and recorded the applicable operating right-of-use asset and corresponding lease liability as of October 5, 2020. Once the purchase is finalized, the Company will take assignment of the Lessor's Ground Lease, in accordance with the Purchase Option, of which lease payments are based on annual payments of $82 thousand, and are subject to a cumulative 10% escalation clause every 5 years through 2071. Refer to Note 11 for additional information. As of December 31, 2020, future minimum commitments under the Company’s operating leases were as follows (in thousands): Operating Leases 2021 $ 1,430 2022 1,464 2023 1,492 2024 1,520 2025 1,555 Thereafter 16,064 Future minimum operating lease payments $ 23,525 Less: Operating lease payments for ASTRA 13,196 Less: Interest 6,383 Present value of lease liability $ 3,946 Supplemental balance sheet information related to leases is as follows: December 31, 2020 December 31, 2019 Operating leases: Right-of-use assets $ 3,298 $ 2,709 Current portion of lease liability 638 480 Lease liability 3,308 2,782 Total lease liability $ 3,946 $ 3,262 Weighted average remaining lease term, in years 16.4 7.2 Weighted average discount rate 9.4 % 8.0 % The Company recorded operating lease costs of $756 thousand and $630 thousand for the years ended December 31, 2020 and 2019, respectively, and variable lease costs of $68 thousand and $39 thousand for the years ended December 31, 2020 and 2019, respectively. Clinical Supply and Product Manufacturing Agreements The Company has entered into various product manufacturing and clinical supply agreements with Contract Manufacturing Organizations (“CMOs”) for the manufacture of clinical trial materials and Contract Research Organizations ("CROs") for clinical trial services. The product manufacturing and clinical supply agreements provide the terms and conditions under which the CMOs and CROs will formulate, fill, inspect, package, label and test our drug product candidates, B-VEC and KB105 for clinical supply. The Company is obligated to make milestone payments. Additionally, certain raw materials, supplies, outsourced testing and other services for the purposes of batch production will be invoiced separately by the CMOs. The estimated remaining commitment as of December 31, 2020 under these agreements for the manufacturing of our drug product is approximately $3.6 million. The Company is also responsible for the payment of a monthly service fee for project management services for the duration of any agreements. The Company has incurred expenses under these agreements of $4.6 million and $4.4 million for the years ended December 31, 2020 and 2019, respectively. Other Contractual Obligations The Company has contracted with various third parties to facilitate, coordinate and perform agreed upon market research activities relating to our lead product candidate, B-VEC. These contracts typically call for the payment of fees for services upon the achievement of certain milestones. Business activities being performed under these contracts primarily include market research and other related activities. The estimated remaining commitment as of December 31, 2020 is $2.7 million. The Company has incurred expenses under these activities of $1.9 million and zero for the years ended December 31, 2020 and 2019, respectively. Legal Proceedings On May 1, 2020, a complaint was filed against us in the United States District Court for the Western District of Pennsylvania by PeriphaGen Inc., which also named our Chief Executive Officer and Chief Operating Officer, Krish Krishnan and Suma Krishnan, respectively. The complaint alleges breach of contract and misappropriation of trade secrets, which secrets the plaintiff asserts were used to develop our product candidates, including the vector backbones, and our STAR-D platform. We answered the complaint on June 26, 2020 by denying the allegations and brought a counterclaim asking the court to declare that we did not misappropriate PeriphaGen’s trade secrets or confidential information, and to further declare that we are the rightful and sole owner of our product candidates and STAR-D platform. In addition, we filed a third-party complaint against two principals of PeriphaGen, James Wechuck and David Krisky, alleging breach of contract and seeking contribution and indemnification from them in the event PeriphaGen is awarded damages. On July 29, 2020, PeriphaGen filed its response to our answer and counterclaim, denying the allegations in the counterclaim. On the same day, Messrs Wechuck and Krisky filed a motion to dismiss the third-party complaint on various grounds, and we have opposed the motion. On December 1, 2020, the court ruled on Messrs. Wechuck and Krisky's motion to dismiss our third-party complaint. The court allowed that our claims on contribution and indemnification based on PeriphaGen's state law claims for unfair competition and misappropriation of trade secrets to go forward. Our breach of contract claim will also go forward in full. While we are unable to provide any assurances as to the ultimate outcome of the case, we believe the allegations in the complaint are without merit, and we intend to vigorously defend against them. We are currently unable to estimate the costs and timing of any litigation, including any potential damages if PeriphaGen were to prevail on its claims.

Capitalization

Capitalization	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Capitalization	Capitalization Sale of Common Stock On November 1, 2017, the Company entered into a stock purchase agreement (the “Agreement”) with the Epidermolysis Bullosa Medical Research Foundation, a California not-for-profit corporation (“EBMRF”), and EB Research Partnership, Inc., a New York not-for-profit corporation (“EBRP” and together with EBMRF, the “Purchasers”), pursuant to which the Company issued and sold to the Purchasers an aggregate of 70,000 shares of the Company’s common stock, par value $0.00001 per share, for a purchase price of $11.00 per share, resulting in aggregate gross proceeds to the Company of $770 thousand (the “Transaction”). The proceeds are to be used exclusively to complete the research plan pursuant to the Agreement. There are redemption features whereby the Company shall repurchase all or a portion of the shares at a purchase price of $11.00 per share or the closing trading price of the common stock on the redemption request date, whichever is higher, should the Company not commence work on or before September 1, 2018 or cease commercially reasonable efforts. The Company did commence work prior to September 1, 2018. As the Company does not intend to cease commercially reasonable efforts, the remaining redemption feature is within the control of the Company and consequently the issued common stock is classified as permanent equity. The offer, sale and issuance of the shares of the Company under the Agreement are exempt from registration pursuant to Rule 506 of Regulation D and Section 4(a)(2) of the Securities Act of 1933, as amended. The Transaction closed on November 2, 2017. On June 27, 2019, the Company completed a public offering of 2,500,000 shares of its common stock to the public at $40.00 per share. Net proceeds to the Company from the offering were $93.8 million after deducting underwriting discounts and commissions of approximately $6.0 million, and other offering expenses payable by the Company of approximately $220 thousand. On July 3, 2019, the underwriters exercised their option to purchase an additional 353,946 shares of common stock at $40.00 per share for additional net proceeds of $13.3 million after deducting underwriting discounts and commissions of approximately $849 thousand. In connection with the public offering, the Company suspended its “at-the-market” equity offering program (“ATM Facility”) that had previously been put in place in March 2019. This program had allowed the Company to sell shares of its common stock for up to $50.0 million in gross proceeds. Following the completion of the offering, $16.8 million remains suspended under this program. As of December 31, 2020 this program has been permanently suspended. On May 21, 2020, the Company completed a public offering of 2,275,000 shares of its common stock to the public at $55.00 per share. Net proceeds to the Company from the offering were $117.2 million after deducting underwriting discounts and commissions of approximately $7.5 million, and other offering expenses payable by the Company of approximately $463 thousand. On December 31, 2020, the Company entered into a sales agreement (the "Sales Agreement") with Cowen and Company, LLC ("Cowen") with respect to an at-the-market equity offering program ("ATM Program"), under which Cowen will act as the Company's agent and/or principal and may issue and sell from time to time, during the term of the Sales Agreement, shares of its common stock, par value $0.0001 per share, having an aggregate offering price up to $150.0 million ("Placement Shares"). The issuance and sale of the Placement Shares by the Company under the Sales Agreement will be made pursuant to the Company's effective "shelf" registration statement on Form S-3. During the year ended December 31, 2020, zero shares of common stock were issued pursuant to the Sales Agreement. Refer to Note 11 for more information.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation Options granted to employees vest ratably over a four-year period and options granted to directors of the company vest ratably over one year and four-year periods. Stock options have a life of ten years. The following table summarizes the Company’s stock option activity: Stock Weighted- Weighted- Aggregate Intrinsic Value (In thousands) (1) Balance at January 1, 2019 357,089 $ 8.73 8.8 $ 4,302 Granted 159,500 33.04 Exercised (72,073) 6.08 Cancelled or forfeited (23,750) 20.82 Balance at December 31, 2019 420,766 $ 17.71 8.4 $ 15,859 Granted 891,250 47.29 Exercised (84,285) 10.45 Cancelled or forfeited (374,117) 38.24 Balance at December 31, 2020 853,614 $ 40.31 9.0 $ 16,804 Exercisable at December 31, 2020 131,125 $ 14.96 7.2 $ 5,905 (1) Aggregate intrinsic value represents the difference between the closing stock price of our common stock on December 31, 2020 and 2019 and the exercise price of outstanding in-the-money options. The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the year ended December 31, 2020 and 2019 was $3.1 million and $2.8 million, respectively. The weighted-average grant-date fair value per share of options granted during the years ended December 31, 2020 and 2019 was $30.99 and $21.72, respectively. There was $18.7 million of unrecognized stock-based compensation expense related to employees’ awards that is expected to be recognized over a weighted-average period of 3.3 years as of December 31, 2020. The Company has recorded aggregate stock-based compensation expense related to the issuance of stock option awards and restricted stock awards to employees and non-employees in the consolidated statements of operations for the years ended December 31, 2020 and 2019 as follows (in thousands): Year Ended December 31, 2020 2019 Research and development $ 994 $ 578 General and administrative 2,278 661 Total stock-based compensation $ 3,272 $ 1,239 We capitalize the portion of stock-based compensation that relates to work performed on the construction of new buildings. There was $34 thousand and zero of stock-based compensation that was capitalized in the years ended December 31, 2020 and 2019, respectively. Stock Options Granted. The Company recorded stock-based compensation expense of $3.3 million and $1.2 million for the years ended December 31, 2020 and 2019, respectively. The fair value of options granted to employees was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions for the years ended December 31, 2020 and 2019: Year Ended December 31, 2020 2019 Expected stock price volatility 75 % 72 % Expected term of the award (years) 6.2 6.1 Risk-free interest rate 0.64 % 2.00 % Exercise price $ 47.29 $ 33.04 Forfeiture Rate 14.74 % 10.00 % Expected dividend yield — % — % Restricted Stock Awards. The Company granted 26,213 and 16,213 restricted stock awards (“RSA”s) on June 1, 2018 to our Chief Executive Officer and Chief Operating Officer, respectively. The RSAs vested ratably over a one-year period and had completely vested as of May 31, 2019. No RSAs were outstanding as of December 31, 2020. The fair value of each restricted stock award was $10.30 reflecting the closing price of our common stock on the grant date. The Company recorded stock-based compensation expense related to RSAs of zero and $182 thousand for the year ended December 31, 2020 and 2019, respectively, within general and administrative expenses in the accompanying consolidated statements of operations. Shares remaining available for grant under the Company's stock incentive plan were 1,690,787, with a sublimit for incentive stock options of 504,815, at December 31, 2020.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes For the years ended December 31, 2020 and 2019, we did not record a current or deferred income tax expense or benefit due to our valuation allowance position. A reconciliation of income tax expense (benefit) computed at the statutory federal and state income tax rate for the year to income tax expense (benefit) as reflected in our financial statements for years ended December 31, 2020 and 2019 are as follows (in thousands): December 31, December 31, 2020 2019 Federal income tax expense (benefit) at statutory rate $ (6,752) $ (4,008) Change in valuation allowance 11,112 6,471 State income tax expense net of federal benefit (2,632) (1,522) Credits (887) (604) Other non-deductible expenses (216) (223) Other (625) (114) Total tax expense (benefit) $ — $ — The significant components of the Company’s deferred tax assets as of December 31, 2020 and 2019 are as follows (in thousands): December 31, December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 19,189 $ 9,934 Stock compensation 664 140 Build-to-suit lease liability 2,893 — Lease liability 1,142 945 Depreciation 123 — Accrued expenses 46 144 Credits 2,311 820 Total deferred tax assets 26,368 11,983 Valuation allowance (22,043) (10,931) Deferred tax assets 4,325 1,052 Deferred tax liabilities: Depreciation — (3) ASTRA Capitalized Construction Costs (2,893) — Right-of-use assets (954) (785) Prepaid expenses (476) (261) Unrealized loss on marketable securities (2) (3) Total deferred tax liabilities (4,325) (1,052) Net deferred tax assets $ — $ — The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of operating losses, the Company has concluded that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2020. As of December 31, 2020 and 2019, the Company had federal research and development credit carryforwards of approximately $1.4 million and $751 thousand, respectively. The federal tax credit carryforwards will begin to expire in 2039 if not utilized. As of December 31, 2020 and 2019, the Company also had orphan drug tax credit carryforwards of approximately $724 thousand and $532 thousand, respectively. The orphan drug tax credit carryforwards will begin to expire in 2038 if not utilized. The Company has not completed a formal research and development credit analysis, and as such, when an analysis is finalized, the Company plans to update its research and development credit carryforward and orphan drug tax credit carryforwards. As of December 31, 2020 and 2019, the Company had state research and development credit carryforwards of approximately $226 thousand and $129 thousand, respectively. The state tax credit carryforwards will begin to expire in 2032 if not utilized. As of December 31, 2020, the Company had cumulative U.S. federal NOL carryforwards of approximately $66.3 million. Of this amount, $5 million is available to offset future income tax liabilities and will expire in 2037, the remaining $61.3 million is available indefinitely to offset future income tax liabilities with no expiration period. Under the provisions of the Internal Revenue Code, the NOL carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOL carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Internal Revenue Code Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future. The Company files income tax returns in the United States at the federal level and in states in which the Company conducts business activities. The federal and state income tax returns are generally subject to tax examinations for the tax year ended December 31, 2017, 2018 and 2019. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service or state tax authorities to the extent utilized in a future period.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party TransactionsIn December 2019 the Company advanced $420 thousand to a member of our management team to cover the personal payroll and income taxes on their taxable income from NSO exercises. This employee repaid the Company in the full amount on January 6, 2020.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Subsequent to December 31, 2020, 262,500 shares of common stock were issued pursuant to the ATM Program for net proceeds of $16.9 million, resulting in a remaining $132.5 million available for issuance under the ATM Program. Refer to Note 7. On January 29, 2021, the Company entered into a Purchase and Sale Agreement ("PSA") for ASTRA with Northfield related to the purchase option exercised by the Company on October 15, 2020 for a purchase price of $9.4 million. The Company currently holds approximately $1.5 million on deposit with Northfield under the existing lease agreement and intends to apply this deposit as a credit against the purchase price at closing. The Agreement contains certain customary representations, warranties and covenants of the parties, and the acquisition of the Property is expected to close in March 2021, subject to the satisfaction of certain customary closing conditions. There can be no assurances that the acquisition will be completed on the expected timeline, on the expected terms or at all. As part of this transaction, the Company will take assignment of the Ground Lease as discussed in Note 6. On February 1, 2021, Northfield delivered the space as substantially complete and made the space available for access by the Company, thus triggering lease commencement. As a result, the Company concluded this transaction did not qualify for sale leaseback accounting because it did not meet the definition of a sale. As control did not transfer to the Lessor, the transaction will continue to be accounted for as construction in progress and a financing obligation. Upon close of the purchase, the Company shall reclassify the construction in progress to buildings and leasehold improvements based on the applicable fair value allocation. From construction completion to the closing of the purchase, the Company will recognize interest expense to accrete the financial obligation to a balance that equals the cash consideration that will be paid upon the close of purchase. On February 1, 2021, the Company completed a public offering of 2,211,538 shares of its common stock, including 288,461 shares purchased by the underwriters, at $65.00 per share. Net proceeds to the Company from the offering were $135.0 million after deducting underwriting discounts and commissions of approximately $8.6 million, and other estimated offering expenses payable by the Company of approximately $193 thousand.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) as found in the Accounting Standards Codification (“ASC”), the Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”) and the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”). All intercompany balances and transactions have been eliminated in consolidation. Certain prior period amounts have been reclassed to conform to the current period presentation. The reclassified amounts have no impact to the Company's previously reported financial position or results of operation.
Use of Estimates	Use of EstimatesThe preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts in the consolidated financial statements and accompanying notes. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements. Estimates are used in the following areas, including: stock-based compensation expense, accrued expenses, the fair value of financial instruments, the incremental borrowing rate for lease liabilities, construction in progress, and the valuation allowance included in the deferred income tax calculation.
Segment and Geographical Information	Segment and Geographical Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company and the Company’s chief operating decision maker view the Company’s operations and manage its business in one operating segment, which is the business of developing and commercializing pharmaceuticals.
Concentrations of Credit Risk and Off-Balance Sheet Risk	Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to credit risk consist of cash, cash equivalents and investments. The Company’s policy is to invest its cash, cash equivalents and investments in money market funds, certificates of deposit, U.S. Treasury bills, and various other bank deposit accounts. The counterparties to the agreements relating to the Company’s investments consist of financial institutions of high credit standing. The Company is exposed to credit risk in the event of default by the financial institutions to the extent amounts recorded on the balance sheets are in excess of insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss.
Cash, Cash Equivalents and Investments	Cash, Cash Equivalents and Investments Cash and cash equivalents consist of money market funds and bank deposits. Cash equivalents are defined as short-term, highly liquid investments with original maturities of 90 days or less at the date of purchase. Investments with maturities of greater than 90 days but less than one year are classified as short-term investments on the consolidated balance sheets and consist of U.S. Treasury bills and certificates of deposit. Investments with maturities of greater than one year are classified as long-term investments on the consolidated balance sheets and consist of certificates of deposit. Accrued interest on U.S. Treasury bills and certificates of deposit are also classified as short-term investments. As our entire investment portfolio is considered available for use in current operations, we classify all investments as available-for-sale securities. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive loss, which is a separate component of stockholders’ equity in the consolidated balance sheets.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. There is a three-level hierarchy that prioritizes the inputs used in determining fair value by their reliability and preferred use, as follows: • Level 1 —Valuations based on quoted prices in active markets for identical assets or liabilities. • Level 2 —Valuations based on quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets and liabilities in inactive markets, or other inputs that are observable, or can be corroborated by observable market data. • Level 3 —Valuations based on inputs that are both significant to the fair value measurement and unobservable. To the extent that a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized within Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. There have been no significant changes to the valuation methods utilized by the Company during the periods presented. There have been no transfers between Level 1, Level 2, and Level 3 in any periods presented. The carrying amounts of financial instruments consisting of cash and cash equivalents, investments, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities included in the Company’s financial statements, are reasonable estimates of fair value, primarily due to their short maturities. Marketable securities are classified as long-term investments if the Company has the ability and intent to hold them and such holding period is longer than one year. The Company classifies all of its investments as available-for-sale. Our available-for-sale, short-term investments, which consist of U.S. Treasury bills and certificates of deposit, are considered to be Level 2 valuations. The fair value of Level 2 financial assets is determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis.
Property and Equipment, net	Property and Equipment, net Property and equipment, net, is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred, while costs of major additions and betterments are capitalized. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Computer equipment and software 3 years Lab equipment 3 - 7 years Furniture and fixtures 3 years Leasehold improvement shorter of 8 years or remaining life of lease Construction-in-progress is not depreciated until the asset is placed in service.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. An impairment loss would be recognized when estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount of the asset. The Company has not recognized any impairment losses for the years ended December 31, 2020 and 2019.
Leases	Leases We have entered into lease agreements for our laboratory, manufacturing and office spaces. On January 1, 2019, we adopted FASB ASC Topic 842, Leases ("ASC 842"). Pursuant to ASC 842, all of our leases outstanding on January 1, 2019 continued to be classified as operating leases. With the adoption of ASC 842, we recorded an operating lease right-of-use asset of $1.1 million and an operating lease liability of $1.4 million on the consolidated balance sheet. Right-of-use lease assets represent our right to use the underlying asset during the lease term and the lease obligations represent our commitment to make lease payments arising from the lease. Right-of-use lease assets and obligations were recognized based on the present value of remaining lease payments over the lease term. As the Company’s lease agreements do not provide an implicit rate and as the Company does not have any external borrowings, we have used an estimated incremental borrowing rate based on the information available at lease commencement in determining the present value of lease payments. The incremental borrowing rate is the rate of interest that the Company would expect to borrow on a collateralized and fully amortizing basis over a similar term an amount equal to the lease payments in a similar economic environment. Operating lease expense is recognized on a straight-line basis over the lease term. Variable lease expense is recognized in the period in which the obligation for the payment is incurred. The Company adopted the new leasing standard as of the effective date of January 1, 2019, with no restatement of prior periods or cumulative adjustment to retained earnings. Upon adoption, the Company took advantage of the transition package of practical expedients permitted within ASC 842, which allowed the Company not to reassess previous accounting conclusions around whether arrangements were, or contained, leases, as well as to carry forward both the historical classification of leases and the treatment of initial direct costs for existing leases. In addition, the Company also has made an accounting policy election to exclude leases with an initial term of twelve months or less from its balance sheet and to account for the lease and non-lease components of its operating leases as a single component. For lease arrangements where it has been determined that the Company has control over an asset that is under construction and is thus considered the accounting owner of the asset during the construction period, the Company records a construction-in-progress asset ("CIP") and corresponding financial obligation on the consolidated balance sheet. Once the construction is complete, an assessment will be performed to determine whether the lease meets certain "sale-leaseback" criteria. If the sale-leaseback criteria are determined to be met, the Company will remove the asset and related financial obligation from the balance sheet and treat the building lease as either an operating or finance lease based on our assessment of the guidance. If, upon completion of construction, the project does not meet the "sale-leaseback" criteria, the lease will be treated as a financing obligation and the Company will depreciate the asset over its estimated useful life for financial reporting purposes.
Research and Development Expenses	Research and Development Expenses Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, facilities and overhead, preclinical and clinical activities, related clinical manufacturing costs, contract management services, regulatory and other related costs. The Company estimates contract research and clinical trials materials manufacturing expenses based on the services performed pursuant to contracts with research and manufacturing organizations that manufacture materials used in the Company’s ongoing preclinical and clinical studies. Non-refundable advanced payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. These estimates are based on communications with third party service providers and the Company’s estimates of accrued expenses using information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly.
Stock-Based Compensation Expense	Stock-Based Compensation Expense The Company accounts for its stock-based compensation awards in accordance with FASB ASC Topic 718, Compensation-Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments, including grants of stock options and restricted stock, to be recognized in the statements of operations based on their grant-date fair values. Compensation expense is recognized on a straight-line basis based on the grant-date fair value over the associated service period of the award, which is generally the vesting term. The Company estimates the fair value of its stock options using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including: (i) the expected stock price volatility; (ii) the expected term of the award; (iii) the risk-free interest rate; and (iv) expected dividends. Due to the lack of sufficient history and trading volume of our common stock and a lack of Company-specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected term of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Due to the lack of Company-specific historical option activity, the Company has estimated the expected term of its employee stock options using the “simplified” method, whereby the expected term equals the arithmetic mean of the vesting term and the original contractual term of the option. The risk-free interest rates are based on U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid and does not expect to pay dividends in the foreseeable future. The Company is also required to estimate forfeitures at the time of grant and to revise
Income Taxes	Income Taxes Income taxes are recorded in accordance with FASB ASC Topic 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. Under this method, we record deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect when the differences are expected to reverse. Valuation allowances are provided when necessary to reduce net deferred tax assets to the amount that is more likely than not to be realized. Based on the available evidence, we are unable, at this time, to support the determination that it is more likely than not that our deferred tax assets will be utilized in the future. Accordingly, we recorded a full valuation allowance as of December 31, 2020. We intend to maintain a valuation allowance until sufficient evidence exists to support its reversal. 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 will more likely than not be realized. 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. As of December 31, 2020, the Company did not have any significant uncertain tax positions.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions from non-owner sources. Unrealized gains or losses on available-for-sale securities is a component of other comprehensive gains or losses and is presented net of taxes. We have not recorded any reclassifications from other comprehensive gains or losses to net loss during any period presented.
Recent Accounting Pronouncements	Recent Accounting Pronouncements ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU 2018-13 - Fair Value Measurement (Topic 820) (“ASU 2018-13”) which removes, modifies and adds disclosure requirements on fair value measurements. ASU 2018-13 removes disclosure requirements for transfers between Level 1 and Level 2 measurements and valuation processes for Level 3 measurements but adds new disclosure requirements including changes in unrealized gains/losses in other comprehensive income related to recurring Level 3 measurements. The amended guidance was effective for the Company in the first quarter of 2020. Certain aspects may be applied prospectively while other aspects may be applied retrospectively upon the effective date. The adoption of the guidance resulted in us disclosing the Company's cash, cash equivalents and available-for-sale securities by significant investment category as of December 31, 2020 and 2019.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Estimated Useful Lives of Assets	Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Computer equipment and software 3 years Lab equipment 3 - 7 years Furniture and fixtures 3 years Leasehold improvement shorter of 8 years or remaining life of lease

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Net Loss Per Share Attributable to Common Stockholders	(In thousands, except share and per share data) Year Ended December 31, 2020 2019 Numerator: Net loss per common share $ (32,167) $ (19,088) Denominator: Weighted-average basic and diluted common shares 18,787,161 15,901,083 Basic and diluted net loss per common share $ (1.71) $ (1.20)

Fair Value Instruments (Tables)

Fair Value Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Cash, Cash Equivalents and Available-for-Sale Securities	The following tables show the Company’s cash, cash equivalents and available-for-sale securities by significant investment category as of December 31, 2020 and 2019, respectively (in thousands): December 31, 2020 Amortized Cost Gross Gross Aggregate Fair Cash and Cash Short-term Marketable Securities (1) Long-term Marketable Securities (2) Level 1: Cash $ 9,463 — — $ 9,463 $ 9,463 — — Money market instruments 258,806 — — 258,806 258,806 — — Subtotal 268,269 — — 268,269 268,269 — — Level 2: U.S. treasury bills — — — — — — — Certificates of deposit 2,986 7 — 2,993 — 2,993 — Subtotal 2,986 7 — 2,993 — 2,993 — Total $ 271,255 $ 7 $ — $ 271,262 $ 268,269 $ 2,993 $ — December 31, 2019 Amortized Cost Gross Gross Aggregate Fair Cash and Cash Short-term Marketable Securities (1) Long-term Marketable Securities (2) Level 1: Cash $ 3 — — $ 3 $ 3 — — Money market instruments 187,511 — — 187,511 187,511 — — Subtotal 187,514 — — 187,514 187,514 — — Level 2: U.S. treasury bills 1,747 6 — 1,753 — 1,753 — Certificates of deposit 4,911 4 — 4,915 — 4,418 497 Subtotal 6,658 10 — 6,668 — 6,171 497 Total $ 194,172 $ 10 $ — $ 194,182 $ 187,514 $ 6,171 $ 497 (1) The Company’s short-term marketable securities mature in one year or less. (2) The Company’s long-term marketable securities mature between one year and two years.

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2020
Balance Sheet Components [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consist of the following (in thousands): December 31, December 31, Construction-in-progress $ 23,031 $ 2,431 Leasehold improvements 4,631 3,179 Furniture and fixtures 870 99 Computer equipment and software 82 45 Laboratory equipment 4,630 3,571 Total property and equipment 33,244 9,325 Accumulated depreciation and amortization (2,368) (850) Property and equipment, net $ 30,876 $ 8,475
Schedule of Accrued Expenses And Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, December 31, Accrued preclinical and clinical expenses $ 1,735 $ 977 Accrued professional fees 642 24 Accrued payroll and benefits 1,486 510 Accrued taxes 40 40 Accrued construction in progress 1,049 263 Other current liabilities 26 12 Accrued financing fees 131 — Total $ 5,109 $ 1,826

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Operating Lease Payments	As of December 31, 2020, future minimum commitments under the Company’s operating leases were as follows (in thousands): Operating Leases 2021 $ 1,430 2022 1,464 2023 1,492 2024 1,520 2025 1,555 Thereafter 16,064 Future minimum operating lease payments $ 23,525 Less: Operating lease payments for ASTRA 13,196 Less: Interest 6,383 Present value of lease liability $ 3,946
Schedule Of Supplemental Condensed Consolidated Balance Sheet Information Related To Leases	Supplemental balance sheet information related to leases is as follows: December 31, 2020 December 31, 2019 Operating leases: Right-of-use assets $ 3,298 $ 2,709 Current portion of lease liability 638 480 Lease liability 3,308 2,782 Total lease liability $ 3,946 $ 3,262 Weighted average remaining lease term, in years 16.4 7.2 Weighted average discount rate 9.4 % 8.0 %

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Schedule of Company's Stock Option Activity	The following table summarizes the Company’s stock option activity: Stock Weighted- Weighted- Aggregate Intrinsic Value (In thousands) (1) Balance at January 1, 2019 357,089 $ 8.73 8.8 $ 4,302 Granted 159,500 33.04 Exercised (72,073) 6.08 Cancelled or forfeited (23,750) 20.82 Balance at December 31, 2019 420,766 $ 17.71 8.4 $ 15,859 Granted 891,250 47.29 Exercised (84,285) 10.45 Cancelled or forfeited (374,117) 38.24 Balance at December 31, 2020 853,614 $ 40.31 9.0 $ 16,804 Exercisable at December 31, 2020 131,125 $ 14.96 7.2 $ 5,905 (1) Aggregate intrinsic value represents the difference between the closing stock price of our common stock on December 31, 2020 and 2019 and the exercise price of outstanding in-the-money options.
Summary of Stock Based Compensation Expense Related to Issuance of Stock Option Awards	The Company has recorded aggregate stock-based compensation expense related to the issuance of stock option awards and restricted stock awards to employees and non-employees in the consolidated statements of operations for the years ended December 31, 2020 and 2019 as follows (in thousands): Year Ended December 31, 2020 2019 Research and development $ 994 $ 578 General and administrative 2,278 661 Total stock-based compensation $ 3,272 $ 1,239
Fair Value of Stock Options, Valuation Assumptions	The fair value of options granted to employees was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions for the years ended December 31, 2020 and 2019: Year Ended December 31, 2020 2019 Expected stock price volatility 75 % 72 % Expected term of the award (years) 6.2 6.1 Risk-free interest rate 0.64 % 2.00 % Exercise price $ 47.29 $ 33.04 Forfeiture Rate 14.74 % 10.00 % Expected dividend yield — % — %

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Summary of Reconciliation of Income Tax Expense (Benefit) Computed at Statutory Federal and State Income Tax Rate	A reconciliation of income tax expense (benefit) computed at the statutory federal and state income tax rate for the year to income tax expense (benefit) as reflected in our financial statements for years ended December 31, 2020 and 2019 are as follows (in thousands): December 31, December 31, 2020 2019 Federal income tax expense (benefit) at statutory rate $ (6,752) $ (4,008) Change in valuation allowance 11,112 6,471 State income tax expense net of federal benefit (2,632) (1,522) Credits (887) (604) Other non-deductible expenses (216) (223) Other (625) (114) Total tax expense (benefit) $ — $ —
Significant Components of Deferred Tax Assets	The significant components of the Company’s deferred tax assets as of December 31, 2020 and 2019 are as follows (in thousands): December 31, December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 19,189 $ 9,934 Stock compensation 664 140 Build-to-suit lease liability 2,893 — Lease liability 1,142 945 Depreciation 123 — Accrued expenses 46 144 Credits 2,311 820 Total deferred tax assets 26,368 11,983 Valuation allowance (22,043) (10,931) Deferred tax assets 4,325 1,052 Deferred tax liabilities: Depreciation — (3) ASTRA Capitalized Construction Costs (2,893) — Right-of-use assets (954) (785) Prepaid expenses (476) (261) Unrealized loss on marketable securities (2) (3) Total deferred tax liabilities (4,325) (1,052) Net deferred tax assets $ — $ —

Organization - Additional Infor

Organization - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Accumulated deficit	$ (71,214)	$ (39,047)
Cash, cash equivalents and short-term investments	$ 271,300

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)	Jan. 01, 2019USD ($)
Significant Accounting Policies [Line Items]
Number of operating segment | segment	1
Right-of-use assets	$ 3,298,000	$ 2,709,000
Total lease liability	3,946,000	3,262,000
Recognized impairment losses for long lived assets	0	0
Accrued interest or penalties related to uncertain tax positions	0	0
Interest and penalties amounts recognized	$ 0	$ 0
ASU 2016-02 | Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Right-of-use assets			$ 1,100,000
Total lease liability			$ 1,400,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2020
Computer equipment and software
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Lab equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Lab equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	7 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Leasehold improvement | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	8 years

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Additional Information (Detail) - shares	Feb. 01, 2021	Feb. 28, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common share equivalents outstanding, excluded from the calculation of diluted net loss per common stockholders (in shares)			853,614	420,766
Subsequent Event
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of shares issued in transaction (in shares)	2,211,538	2,474,038

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss Per Share and Per Unit (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss per common share	$ (32,167)	$ (19,088)
Denominator:
Weighted-average basic and diluted common shares (in shares)	18,787,161	15,901,083
Basic and diluted net loss per common share (in usd per share)	$ (1.71)	$ (1.20)

Fair Value Instruments - Summar

Fair Value Instruments - Summary of Cash, Cash Equivalents and Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 268,269	$ 187,514
Gross Unrealized Gains	7	10
Gross Unrealized Losses		0
Amortized cost, total	271,255	194,172
Aggregate fair value, total	271,262	194,182
Level 1:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	268,269	187,514
Level 2:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	2,986	6,658
Gross Unrealized Gains	7	10
Gross Unrealized Losses		0
Aggregate Fair Value	2,993	6,668
Cash | Level 1:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	9,463	3
Money market instruments | Level 1:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	258,806	187,511
U.S. treasury bills | Level 2:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	0	1,747
Gross Unrealized Gains	0	6
Aggregate Fair Value	0	1,753
Certificates of deposit | Level 2:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	2,986	4,911
Gross Unrealized Gains	7	4
Gross Unrealized Losses		0
Aggregate Fair Value	2,993	4,915
Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate fair value, total	268,269	187,514
Cash and Cash Equivalents | Level 1:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, aggregate fair value	268,269	187,514
Cash and Cash Equivalents | Cash | Level 1:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, aggregate fair value	9,463	3
Cash and Cash Equivalents | Money market instruments | Level 1:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, aggregate fair value	258,806	187,511
Short-term Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate fair value, total	2,993	6,171
Short-term Marketable Securities | Level 2:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	$ 2,993	6,171
Debt securities, available-for-sale, term	1 year
Short-term Marketable Securities | U.S. treasury bills | Level 2:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	$ 0	1,753
Short-term Marketable Securities | Certificates of deposit | Level 2:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	2,993	4,418
Long-term Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate fair value, total	0	497
Long-term Marketable Securities | Level 2:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	$ 0	497
Long-term Marketable Securities | Level 2: | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, term	1 year
Long-term Marketable Securities | Level 2: | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, term	2 years
Long-term Marketable Securities | Certificates of deposit | Level 2:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	$ 0	$ 497

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 33,244	$ 9,325
Accumulated depreciation and amortization	(2,368)	(850)
Property and equipment, net	30,876	8,475
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property and equipment	23,031	2,431
Leasehold improvement
Property, Plant and Equipment [Line Items]
Total property and equipment	4,631	3,179
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	870	99
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	82	45
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 4,630	$ 3,571

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Components [Abstract]
Depreciation expense	$ 1,500	$ 748

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Accrued Expenses And Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Components [Abstract]
Accrued preclinical and clinical expenses	$ 1,735	$ 977
Accrued professional fees	642	24
Accrued payroll and benefits	1,486	510
Accrued taxes	40	40
Accrued construction in progress	1,049	263
Other current liabilities	26	12
Accrued financing fees	131	0
Total	$ 5,109	$ 1,826

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Oct. 15, 2020USD ($)	May 31, 2016	Dec. 31, 2020USD ($)ft²	Dec. 31, 2020USD ($)ft²	Dec. 31, 2019USD ($)	Jan. 21, 2020USD ($)	Dec. 26, 2019ft²
Operating Leased Assets [Line Items]
Lease expiration date				Feb. 28, 2027
Additional area of real estate property leased | ft²			3,800	3,800
Lease termination date				Oct. 31, 2035
Cash contribution						$ 2,400,000
Purchase price of potential building purchase	$ 9,400,000
Finance Lease, Liability						10,000,000
Construction in Progress, Gross						$ 10,000,000
Escrow deposit	$ 1,500,000
Annual lease payments			$ 82,000
Cumulative escalation clause, percent	0.10
Cumulative escalation clause, term	5 years
Operating lease costs				$ 756,000	$ 630,000
Variable lease cost				68,000	39,000
Clinical Supply Agreements
Operating Leased Assets [Line Items]
Estimated remaining commitment			3,600,000	3,600,000
Project management service fee				4,600,000	4,400,000
Other Contractual Obligations
Operating Leased Assets [Line Items]
Estimated remaining commitment			$ 2,700,000	2,700,000
Project management service fee				$ 1,900,000	$ 0
Pennsylvania
Operating Leased Assets [Line Items]
Facility, square foot area | ft²							150,000
2016 Lease Agreement
Operating Leased Assets [Line Items]
Lease expiration date		Oct. 31, 2017
Additional area of real estate property leased | ft²			29,000	29,000
ANCORIS
Operating Leased Assets [Line Items]
Additional area of real estate property leased | ft²			7,500	7,500

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Operating Lease Payments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating Leased Assets [Line Items]
2021	$ 1,430
2022	1,464
2023	1,492
2024	1,520
2025	1,555
Thereafter	16,064
Future minimum operating lease payments	23,525
Less: Interest	6,383
Present value of lease liability	3,946	$ 3,262
A S T R A Facility
Operating Leased Assets [Line Items]
Future minimum operating lease payments	$ 13,196

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Supplemental Condensed Consolidated Balance Sheet Information Related to Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Right-of-use assets	$ 3,298	$ 2,709
Current portion of lease liability	638	480
Lease liability	3,308	2,782
Total lease liability	$ 3,946	$ 3,262
Weighted average remaining lease term, in years	16 years 4 months 24 days	7 years 2 months 12 days
Weighted average discount rate	9.40%	8.00%

Capitalization - Additional Inf

Capitalization - Additional Information (Detail) - USD ($)	May 21, 2020	Jul. 03, 2019	Jun. 27, 2019	Nov. 01, 2017	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Schedule of Capitalization, Equity [Line Items]
Common stock, par value (in usd per share)					$ 0.00001	$ 0.00001	$ 0.00001
Proceeds from issue of common stock						$ 118,019,000	$ 107,525,000
Over-Allotment Option
Schedule of Capitalization, Equity [Line Items]
Issuance of common stock (in shares)		353,946
Shares issued, price per share (in usd per share)		$ 40
Proceeds from issue of common stock		$ 13,300,000
Underwriting discounts and commissions		$ 849,000
Public Offering
Schedule of Capitalization, Equity [Line Items]
Issuance of common stock (in shares)	2,275,000		2,500,000
Shares issued, price per share (in usd per share)	$ 55		$ 40
Underwriting discounts and commissions	$ 7,500,000		$ 6,000,000
Proceeds from initial offering of shares	117,200,000		93,800,000
Adjustments to additional paid in capital, stock issued, issuance costs	$ 463,000		220,000
ATM Facilty
Schedule of Capitalization, Equity [Line Items]
Agreed sale price of shares			50,000,000
Common stock value suspended			$ 16,800,000
Stock Purchase Agreement
Schedule of Capitalization, Equity [Line Items]
Issuance of common stock (in shares)					70,000
Common stock, par value (in usd per share)				$ 0.00001
Shares issued, price per share (in usd per share)				$ 11
Proceeds from issue of common stock					$ 770,000
Transaction closing date				Nov. 2, 2017
Stock Sale Agreement | Placement Shares
Schedule of Capitalization, Equity [Line Items]
Issuance of common stock (in shares)						0
Common stock, par value (in usd per share)					$ 0.0001	$ 0.0001
Aggregate offering price					$ 150,000,000	$ 150,000,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expiration period	10 years
Intrinsic value of options exercised	$ 3,100	$ 2,800
Share-based payment arrangement, amount capitalized	34	0
Stock-based compensation expense	$ 3,272	$ 1,239
Stock options granted (in shares)	891,250	159,500
Stock options available for grant (in shares)	1,690,787
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	4 years
Weighted-average grant-date fair value per share of options granted (in usd per share)	$ 30.99	$ 21.72
Unrecognized stock-based compensation expense	$ 18,700
Estimated weighted average period	3 years 3 months 18 days
Non-Employee Stock Option | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	1 year
Non-Employee Stock Option | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	4 years
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	1 year
Weighted-average grant-date fair value per share of options granted (in usd per share)	$ 10.30
Stock-based compensation expense	$ 0	$ 182
Restricted stock award outstanding (in shares)	0
Restricted Stock | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock award granted (in shares)	26,213
Restricted Stock | Chief Operating Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock award granted (in shares)	16,213
Incentive Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options available for grant (in shares)	504,815

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Company's Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock Options Outstanding
Beginning balance (in shares)	420,766	357,089
Granted (in shares)	891,250	159,500
Exercised (in shares)	(84,285)	(72,073)
Cancelled or forfeited (in shares)	(374,117)	(23,750)
Ending balance (in shares)	853,614	420,766	357,089
Exercisable at December 31, 2020 (in shares)	131,125
Weighted- average Exercise Price
Beginning balance (in usd per share)	$ 17.71	$ 8.73
Granted (in usd per share)	47.29	33.04
Exercised (in usd per share)	10.45	6.08
Cancelled or forfeited (in usd per share)	38.24	20.82
Ending balance (in usd per share)	40.31	$ 17.71	$ 8.73
Exercisable at December 31, 2020 (in usd per share)	$ 14.96
Weighted- average Remaining Contractual Life (Years)
Weighted-average remaining contractual life (years)	9 years	8 years 4 months 24 days	8 years 9 months 18 days
Weighted-average remaining contractual Life (years), exercisable	7 years 2 months 12 days
Aggregate Intrinsic Value
Aggregate intrinsic value, outstanding	$ 16,804	$ 15,859	$ 4,302
Aggregate Intrinsic Value, Exercisable	5,905
Intrinsic value of options exercised	$ 3,100	$ 2,800

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Based Compensation Expense Related to Issuance of Stock Option Awards (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 3,272	$ 1,239
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	994	578
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 2,278	$ 661

Stock-Based Compensation - Fair

Stock-Based Compensation - Fair Value of Stock Options, Valuation Assumptions (Detail) - Employee Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected stock price volatility	75.00%	72.00%
Expected term of the award (years)	6 years 2 months 12 days	6 years 1 month 6 days
Risk-free interest rate	0.64%	2.00%
Exercise price	$ 47.29	$ 33.04
Forfeiture Rate	14.74%	10.00%
Expected dividend yield	0.00%	0.00%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Current income tax expense (benefit)	$ 0	$ 0
Deferred income tax expense (benefit)	0	0
Cumulative NOL carry forwards	$ 19,189,000	9,934,000
Cumulative changes in ownership interest rate period	3 years
Orphan Drug Tax Credit Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount	$ 724,000	532,000
Minimum
Income Taxes [Line Items]
Cumulative changes in ownership interest of shareholders	50.00%
U.S. Federal
Income Taxes [Line Items]
Cumulative NOL carry forwards	$ 66,300,000
Cumulative NOL carry forwards with expiration	$ 5,000,000
Operating loss carryforward expiration year	2037
Cumulative NOL carry forwards with no expiration	$ 61,300,000
U.S. Federal | Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount	1,400,000	751,000
State and Local Jurisdiction | Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount	$ 226,000	$ 129,000

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Income Tax Expense (Benefit) Computed at Statutory Federal and State Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal income tax expense (benefit) at statutory rate	$ (6,752)	$ (4,008)
Change in valuation allowance	11,112	6,471
State income tax expense net of federal benefit	(2,632)	(1,522)
Credits	(887)	(604)
Other non-deductible expenses	(216)	(223)
Other	(625)	(114)
Total tax expense (benefit)	$ 0	$ 0

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 19,189	$ 9,934
Stock compensation	664	140
Build-to-suit lease liability	2,893	0
Lease liability	1,142	945
Depreciation	123	0
Accrued expenses	46	144
Credits	2,311	820
Total deferred tax assets	26,368	11,983
Valuation allowance	(22,043)	(10,931)
Deferred tax assets	4,325	1,052
Deferred tax liabilities:
Depreciation	0	(3)
ASTRA Capitalized Construction Costs	(2,893)	0
Right-of-use assets	(954)	(785)
Prepaid expenses	(476)	(261)
Unrealized loss on marketable securities	(2)	(3)
Total deferred tax liabilities	(4,325)	(1,052)
Net deferred tax assets	$ 0	$ 0

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) $ in Thousands	1 Months Ended
	Dec. 31, 2019USD ($)
Management
Related Party Transaction [Line Items]
Advance to management team	$ 420

Subsequent Events (Details)

Subsequent Events (Details) - USD ($)	Feb. 01, 2021	Mar. 31, 2021	Mar. 01, 2021	Feb. 28, 2021	Jan. 29, 2021
Forecast
Subsequent Event [Line Items]
Payments to Acquire Real Estate Held-for-investment		$ 9,400,000
Subsequent Event
Subsequent Event [Line Items]
Number of shares issued in transaction (in shares)	2,211,538			2,474,038
Consideration received on transaction	$ 135,000,000
Deposits assets					$ 1,500,000
Sale of stock, price per share (in usd per share)	$ 65
Sale of stock, discounts and commissions	$ 8,600,000
Payments of stock issuance costs	$ 193,000
Subsequent Event | ATM Program
Subsequent Event [Line Items]
Number of shares issued in transaction (in shares)			262,500
Consideration received on transaction			$ 16,900,000
Remaining available issuance amount			$ 132,500,000
Subsequent Event | Over-Allotment Option
Subsequent Event [Line Items]
Number of shares issued in transaction (in shares)	288,461