Allakos (ALLK) 10-Q 10 May 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 07, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Trading Symbol	ALLK
Entity Registrant Name	Allakos Inc.
Entity Central Index Key	0001564824
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		53,569,720
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38582
Entity Tax Identification Number	45-4798831
Entity Address, Address Line One	975 Island Drive
Entity Address, Address Line Two	Suite 201
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94065
City Area Code	650
Local Phone Number	597-5002
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.001
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE

BALANCE SHEETS (Unaudited)

BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 169,989	$ 207,177
Investments in marketable securities	445,945	451,820
Prepaid expenses and other current assets	13,015	10,270
Total current assets	628,949	669,267
Property and equipment, net	13,620	8,345
Operating lease right-of-use assets	38,924	39,731
Other long-term assets	2,275	2,275
Total assets	683,768	719,618
Current liabilities:
Accounts payable	9,911	13,960
Accrued expenses and other current liabilities	12,976	8,490
Total current liabilities	22,887	22,450
Operating lease liabilities, net of current portion	44,827	42,773
Total liabilities	67,714	65,223
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock, $0.001 par value per share; 20,000 shares authorized as of March 31, 2021 and December 31, 2020; no shares issued and outstanding as of March 31, 2021 and December 31, 2020	0	0
Common stock, $0.001 par value per share; 200,000 shares authorized as of March 31, 2021 and December 31, 2020; 53,457 and 53,081 shares issued and outstanding as of March 31, 2021 and December 31, 2020, respectively	53	53
Additional paid-in capital	1,014,435	997,298
Accumulated other comprehensive gain	88	8
Accumulated deficit	(398,522)	(342,964)
Total stockholders’ equity	616,054	654,395
Total liabilities and stockholders’ equity	$ 683,768	$ 719,618

BALANCE SHEETS (Unaudited) (Par

BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	53,457,000	53,081,000
Common stock, shares outstanding	53,457,000	53,081,000

STATEMENTS OF OPERATIONS AND CO

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses
Research and development	$ 38,915	$ 18,285
General and administrative	16,670	11,588
Total operating expenses	55,585	29,873
Loss from operations	(55,585)	(29,873)
Interest income	130	1,989
Other income (expense), net	(103)	60
Net loss	(55,558)	(27,824)
Unrealized gain on marketable securities	80	1,869
Comprehensive loss	$ (55,478)	$ (25,955)
Net loss per common share:
Basic and diluted	$ (1.04)	$ (0.57)
Weighted-average number of common shares outstanding:
Basic and diluted	53,186	48,691

STATEMENTS OF STOCKHOLDERS' EQU

STATEMENTS OF STOCKHOLDERS' EQUITY (unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Gain	Accumulated Deficit
Balance at Dec. 31, 2019	$ 495,721	$ 48	$ 685,020	$ 137	$ (189,484)
Balance, Shares at Dec. 31, 2019		48,668
Stock-based compensation expense	7,489	$ 0	7,489	0	0
Issuance of common stock upon exercise of stock options	33	$ 0	33	0	0
Issuance of common stock upon exercise of stock options, Shares		57
Issuance of common stock upon 2018 ESPP purchase	756	$ 0	756	0	0
Issuance of common stock upon 2018 ESPP purchase, Shares		40
Unrealized gain on marketable securities	1,869	$ 0	0	1,869	0
Net loss	(27,824)	0	0	0	(27,824)
Balance at Mar. 31, 2020	478,044	$ 48	693,298	2,006	(217,308)
Balance, Shares at Mar. 31, 2020		48,765
Balance at Dec. 31, 2020	654,395	$ 53	997,298	8	(342,964)
Balance, Shares at Dec. 31, 2020		53,081
Stock-based compensation expense	12,354	$ 0	12,354	0	0
Issuance of common stock upon exercise of stock options	$ 3,788	$ 0	3,788	0	0
Issuance of common stock upon exercise of stock options, Shares	321	321
Issuance of common stock upon 2018 ESPP purchase	$ 995	$ 0	995	0	0
Issuance of common stock upon 2018 ESPP purchase, Shares		17
Issuance of common stock upon vesting of restricted stock units	0	$ 0	0	0	0
Issuance of common stock upon vesting of restricted stock units, Shares		38
Unrealized gain on marketable securities	80	$ 0	0	80	0
Net loss	(55,558)	0	0	0	(55,558)
Balance at Mar. 31, 2021	$ 616,054	$ 53	$ 1,014,435	$ 88	$ (398,522)
Balance, Shares at Mar. 31, 2021		53,457

STATEMENTS OF CASH FLOWS (unaud

STATEMENTS OF CASH FLOWS (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net loss	$ (55,558)	$ (27,824)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	372	393
Stock-based compensation	12,354	7,489
Net amortization of premiums and discounts on marketable securities	465	221
Noncash lease expense	807	70
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,458)	(113)
Accounts payable	(6,791)	3,092
Accrued expenses and other current liabilities	3,823	(1,942)
Operating lease liabilities, net of current portion	727	0
Net cash used in operating activities	(46,259)	(18,614)
Cash flows from investing activities
Purchases of marketable securities	(174,797)	(15,052)
Proceeds from maturities of marketable securities	180,000	130,500
Purchases of property and equipment	(915)	(48)
Net cash provided by investing activities	4,288	115,400
Cash flows from financing activities
Proceeds from exercise of stock options	3,788	33
Proceeds from issuance of common stock under the 2018 ESPP	995	756
Net cash provided by financing activities	4,783	789
Net increase (decrease) in cash, cash equivalents and restricted cash	(37,188)	97,575
Cash, cash equivalents and restricted cash, beginning of period	209,452	40,642
Cash, cash equivalents and restricted cash, end of period	172,264	138,217
Noncash investing and financing items:
Lessor funded lease incentives included in property and equipment	1,466	0
Property and equipment purchased, not yet paid	$ 3,266	$ 7

Organization and Business

Organization and Business	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Business	1. Organization and Business Allakos Inc. (“Allakos” or the “Company”) was incorporated in the state of Delaware in March 2012. Allakos is a clinical stage biopharmaceutical company focused on the development of lirentelimab (AK002) for the treatment of eosinophil and mast cell related diseases. The Company’s primary activities to date have included establishing its facilities, recruiting personnel, conducting research and development of its product candidates and raising capital. The Company’s operations are located in Redwood City, California. Liquidity Matters Since inception, the Company has incurred net losses and negative cash flows from operations. During the three months ended March 31, 2021, the Company incurred a net loss of $55.6 million and used $46.3 million of cash in operations. At March 31,

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The unaudited interim financial statements have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts and disclosures reported in the financial statements and accompanying notes. The interim balance sheet as of March 31, 2021, the statements of operations and comprehensive loss, statements of stockholders’ equity and statements of cash flows for the three months ended March 31, 2021 and 2020 are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair presentation of the Company’s financial position as of March 31, 2021 and its results of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 and its cash flows for the three months ended March 31, 2021 and 2020. Certain information and note disclosures normally included in annual audited financial statements prepared in accordance with U.S. GAAP have been omitted. The financial data and the other financial information disclosed in these notes to the interim financial statements are also unaudited. The results of operations for any interim period are not necessarily indicative of the results to be expected for the entire year or for any other future annual or interim period. The balance sheet as of March 31, 2021 included herein was derived from the audited financial statements as of that date. These interim financial statements should be read in conjunction with the Company’s audited financial statements included in the Company’s Annual Report on Form 10-K, which was filed with the Securities and Exchange Commission (the “SEC”) on March 1, 2021. Use of Estimates Management uses significant judgment when making estimates related to common stock valuation and related stock-based compensation expense, accrued research and development expense, and deferred tax valuation allowances. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates under different assumptions or conditions, and those differences could be material to the financial position and results of operations. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to credit risk principally consist of cash, cash equivalents and marketable securities. These financial instruments are held in accounts at a single financial institution that management believes possesses high credit quality. Amounts on deposit with this financial institution have and will continue to exceed federally-insured limits. The Company has not experienced any losses on its cash deposits. Additionally, the Company’s investment policy limits its investments to certain types of securities issued by or backed by the U.S. government and its agencies. The Company is subject to a number of risks similar to that of other clinical stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of current or future clinical trials, its reliance on third-parties to conduct its clinical trials, the need to obtain regulatory and marketing approvals for its product candidates, competitive developments, the need to successfully commercialize and gain market acceptance of the Company’s product candidates, its right to develop and commercialize its product candidates pursuant to the terms and conditions of the licenses granted to the Company, protection of proprietary technology, the ability to make milestone, royalty or other payments due under licensing agreements, and the need to secure and maintain adequate manufacturing arrangements with third-parties. If the Company does not successfully commercialize or partner its product candidates, it will be unable to generate product revenue or achieve profitability. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the accompanying statements of cash flows (in thousands): March 31, December 31, 2021 2020 Cash and cash equivalents $ 169,989 $ 207,177 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 172,264 $ 209,452 March 31, December 31, 2020 2019 Cash and cash equivalents $ 135,942 $ 38,367 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 138,217 $ 40,642 Restricted cash at March 31, 2021 represents $2.3 million in deposits for the lease of the Company’s facilities in Redwood City, California and San Carlos, California. Both security deposits are in the form of letters of credit secured by restricted cash. Restricted cash amounts are included within other long-term assets on the Company’s balance sheets. Marketable Securities The Company invests in marketable securities, primarily securities issued by the United States government and its agencies. The Company’s marketable securities are considered available-for-sale and are classified as current assets even when the stated maturities of the underlying securities exceed one year from the date of the current balance sheet being reported. This classification reflects management’s ability and intent to utilize proceeds from the sale of such investments to fund ongoing operations. Unrealized gains and losses are excluded from earnings and are reported as a component of accumulated other comprehensive gain. The cost of securities sold is determined using the specific-identification method. Interest earned and adjustments for the amortization of premiums and discounts on investments are included in interest income, net, on the statements of operations and comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on investments in marketable securities are included in other expense, net, on the statements of operations and comprehensive loss. Operating Leases Effective January 1, 2019, the Company accounts for its leases in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 842, “Leases” (“ASC 842”). As part of this transition, the Company elected a number of optional practical expedients made available under the ASC 842 transition guidance including (i) carrying forward the Company’s historical lease classifications, (ii) foregoing of re-evaluation of historical contracts using ASC 842’s definition of a lease, (iii) foregoing a re-assessment of initial direct costs related to leases that existed prior to adoption, (iv) combining lease and non-lease components for all classes of assets, and (v) recognizing lease expense for all contracts with an initial term of 12 months or less within the statements of operations and comprehensive loss on a straight-line basis over the requisite lease term. Under ASC 842, the Company accounts for its leases by recording right-of-use assets and lease liabilities on the balance sheets. Right-of-use assets represent the Company’s right to use an underlying asset over the lease term and include any lease payments made prior to the lease commencement date and are reduced by lease incentives. Lease liabilities represent the present value of the total lease payments over the lease term, calculated using the Company’s incremental borrowing rate. In determining the Company’s incremental borrowing rate, consideration is given to the term of the lease and the Company’s credit risk. The Company recognizes options to extend a lease when it is reasonably certain that it will exercise such extension. The Company does not recognize options to terminate a lease when it is reasonably certain that it will not exercise such early termination options. Lease expense is recognized on a straight-line basis over the expected lease term. Prior to the Company’s adoption of ASC 842, the Company accounted for its leases in accordance with FASB ASC 840, Leases (“ASC 840”). Under ASC 840, r ent expense is recorded on a straight-line basis over the term of the lease. Differences that exist between cash rent payments and the recognition of rent expense, such as those resulting from rent abatements or contractual escalations of future lease payments, are recorded as a deferred rent liability and recognized as adjustments to rental expense on a straight-line basis over the term of the lease. The current portion of the deferred rent liability is included within accrued expenses and other current liabilities on the Company’s balance sheet s with remainder included within operating lease liabilities, net of current portion . Tenant improvement allowances received are recorded as lease incentive obligations included in accrued expenses and other current liabilities and operating lease liabilities , net of current portion on the Company’s balance sheets and amortized to rent expense over the term of the lease . Accrued Research and Development Expense Service agreements with contract development and manufacturing organizations (“CDMOs”), clinical contract research organizations (“CROs”) and clinical investigative sites comprise a significant component of the Company’s research and development activities. External costs for these vendors are recognized as the services are incurred. The Company accrues for expenses resulting from obligations under agreements with its third-parties for which the timing of payments does not match the periods over which the materials or services are provided to the Company. Accruals are recorded based on estimates of services received and efforts expended pursuant to agreements established with CDMOs, clinical CROs, clinical investigative sites and other outside service providers. These estimates are typically based on contracted amounts applied to the proportion of work performed and determined through analysis with internal personnel and external service providers as to the progress or stage of completion of the services. The Company makes judgements and estimates in determining the accrual balance in each reporting period. In the event advance payments are made to a CDMO, clinical CRO, clinical investigative site or other outside service provider, the payments are recorded within prepaid expenses and other current assets and subsequently recognized as research and development expense when the associated services have been performed. As actual costs become known, the Company adjusts its liabilities and assets. Inputs, such as the extent of services received and the duration of services to be performed, may vary from the Company’s estimates, which will result in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. The Company’s historical estimates have not been materially different from actual amounts recorded . Research and Development Expense Research and development costs are expensed as incurred. Research and development costs include, among others, consulting costs, salaries, benefits, travel, stock-based compensation, laboratory supplies and other non-capital equipment utilized for in-house research, allocation of facilities and overhead costs and external costs paid to third-parties that conduct research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements, including milestone payments, are also included in research and development expense. Advance payments for goods or services to be rendered in the future for use in research and development activities are deferred and included in prepaid expenses and other current assets. The deferred amounts are expensed as the related goods are delivered or the services are performed. Comprehensive Loss Comprehensive loss is defined as the change in stockholders’ equity (deficit) during a period from transactions and other events and circumstances from non-owner sources. The difference between net loss and comprehensive loss for the three months ended March 31, 2021 and 2020 are a result of unrealized gains and losses on the Company’s investments in marketable securities included in current assets on the balance sheets. Net Loss per Share The Company calculates basic net loss per share by dividing the net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. The Company calculates diluted net loss per share after giving consideration to all potentially dilutive securities outstanding during the period using the treasury-stock and if-converted methods, except where the effect of including such securities would be Basic and diluted net loss per share was calculated as follows (in thousands, except per share data): Three Months Ended March 31, 2021 2020 Numerator: Net loss $ (55,558 ) $ (27,824 ) Denominator: Weighted-average shares of common stock outstanding, basic and diluted 53,186 48,691 Net loss per share, basic and diluted $ (1.04 ) $ (0.57 ) The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect for the periods indicated (in thousands): Three Months Ended March 31, 2021 2020 Options to purchase common stock 6,251 7,105 Unvested restricted stock units 1,093 572 Shares issuable under employee stock purchase plans 4 8 Total 7,348 7,685 Recently Issued and Adopted Accounting Pronouncements The Company has reviewed recently issued accounting pronouncements and concluded they are either not applicable to the business or that no material effect is expected on the Company’s financial statements as a result of future adoption. Impact of Recent Legislation In March 2020, the Coronavirus Aid, Relief and Economic Security Act (“the CARES Act”) was signed into law. The CARES Act includes provisions relating to several aspects of corporate income taxes. The Company does not currently expect the CARES Act to have a material impact on its income tax positions; however, it will continue to monitor the provisions of the CARES Act in relation to its operations .

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company measures and reports certain financial instruments as assets and liabilities at fair value on a recurring basis. The Company’s financial assets measured at fair value on a recurring basis were as follows (in thousands): March 31, 2021 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 168,754 $ — $ — $ 168,754 Total cash equivalents 168,754 — — 168,754 Short-term marketable securities U.S. treasuries 445,945 — — 445,945 Total short-term marketable securities 445,945 — — 445,945 Total cash equivalents and short-term marketable securities $ 614,699 $ — $ — $ 614,699 December 31, 2020 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 205,408 $ — $ — $ 205,408 Total cash equivalents 205,408 — — 205,408 Short-term marketable securities U.S. treasuries 451,820 — — 451,820 Total short-term marketable securities 451,820 — — 451,820 Total cash equivalents and short-term marketable securities $ 657,228 $ — $ — $ 657,228 The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of assets or liabilities between levels during the three months ended March 31, 2021 and 2020.

Marketable Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2021
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities All marketable securities were considered available-for-sale at March 31, 2021. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type at March 31, 2021 and December 31, 2020 are summarized in the table below (in thousands): March 31, 2021 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Available-for-sale securities U.S. treasuries classified as investments $ 445,857 $ 88 $ — $ 445,945 Total available-for-sale securities $ 445,857 $ 88 $ — $ 445,945 December 31, 2020 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Available-for-sale securities U.S. treasuries classified as investments $ 451,812 $ 26 $ (18 ) $ 451,820 Total available-for-sale securities $ 451,812 $ 26 $ (18 ) $ 451,820 The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. As of March 31, 2021, the Company had no securities in an unrealized loss position. As of December 31, 2020, the aggregate fair value of securities held by the Company in an unrealized loss position was $91.4 million. All of these securities had remaining maturities of less than one year. The Company has the intent and ability to hold such securities until recovery and has determined that there has been no material change to their credit risk. As a result, the Company determined it did not hold any investments with a credit loss at March 31, 2021 and December 31, 2020. There were no material realized gains or losses recognized on the sale or maturity of available-for-sale securities during the three months ended March 31, 2021 and 2020, and as a result, there were no material reclassifications out of accumulated other comprehensive gain (loss) for the same periods.

Balance Sheet Components and Su

Balance Sheet Components and Supplemental Disclosures	3 Months Ended
	Mar. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components and Supplemental Disclosures	5. Balance Sheet Components and Supplemental Disclosures Property and Equipment, Net Property and equipment, net, consisted of the following (in thousands): March 31, December 31, 2021 2020 Laboratory equipment $ 4,232 $ 4,236 Furniture and office equipment 1,784 1,784 Leasehold improvements 4,581 4,581 Construction-in-progress 6,964 1,325 17,561 11,926 Less accumulated depreciation (3,941 ) (3,581 ) Property and equipment, net $ 13,620 $ 8,345 Depreciation and amortization expense for each of the three months ended March 31, 2021 and 2020 was $0.4 million. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): March 31, December 31, 2021 2020 Accrued contract research and development expense $ 8,091 $ 4,697 Accrued compensation and benefits expense 3,798 3,214 Current portion of operating lease liabilities 514 492 Other current liabilities 573 87 Total $ 12,976 $ 8,490

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Operating Leases The Company’s lease obligations primarily relate to leased office and laboratory space under noncancelable operating leases. In accordance with ASC 842, the Company has performed an evaluation of its other contracts with vendors and has determined that, except for the leases described below, none of its other contracts contain a lease 2018 Redwood City Lease In January 2018, the Company entered into an operating lease agreement for approximately 25,000 square feet of office and laboratory space in Redwood City, California (the “2018 Redwood City Lease”). The contractual term of the 2018 Redwood City Lease is 10.75 years beginning from the substantial completion and delivery of the premises, which occurred in November 2018, and terminating in July 2029. The 2018 Redwood City Lease provides rent abatements and includes a one-time option to extend the lease term for five years. This option to extend the lease term was not determined to be reasonably certain and therefore has not been included in the Company’s calculation of the associated operating lease liability under ASC 842 The 2018 Redwood City Lease includes monthly base rent amounts escalating over the term of the lease. In addition, the lessor provided for a tenant improvement allowance ("TIA") of up to $1.4 million, which was fully utilized. The TIA was recorded as leasehold improvements, with offsetting adjustments recorded to the associated operating lease right of use asset included on the balance sheets as of March 31, 2021 and December 31, 2020. The Company utilized its incremental borrowing rate to calculate the present value of the lease payments for the 2018 Redwood City Lease based on information available on January 1, 2019, the adoption date of ASC 842. 2019 San Carlos Lease In December 2019, the Company entered into an additional operating lease agreement for approximately 98,000 and terminate in September 2031 . The 2019 San Carlos Lease provides rent abatements and includes a one-time option to extend the lease term for five years . This option to extend the lease term was not determined to be reasonably certain and therefore has not been included in the Company’s calculation of the associated operating lease liability under ASC 842. The 2019 San Carlos Lease includes monthly base rent amounts escalating over the term of the lease. In addition, the lessor provided for a TIA of up to $14.7 million, which is expected to be fully utilized. The TIA was recorded as construction-in-progress, and included within property and equipment, net on the balance sheets as of March 31, 2021 and December 31, 2020. The Company utilized its incremental borrowing rate to calculate the present value of the lease payments for the 2019 San Carlos Lease based on information available on November 1, 2020, the lease commencement date for accounting purposes, which was the date the Company was deemed to have obtained control of the premises. Calculation of the operating lease liability also included estimated future TIA reimbursements that had not yet been received as of the lease commencement date. TIA reimbursements received subsequent to lease commencement date are recorded as reductions to the operating lease liability. Classification of Operating Leases The 2018 Redwood City Lease and the 2019 San Carlos Lease required security deposits of $0.8 million and $1.5 million, respectively, which the Company satisfied by establishing letters of credit secured by restricted cash. Restricted cash related to the Company’s lease agreements are recorded in other long-term assets on the Company’s balance sheets. Classification of the Company’s operating lease liabilities included on its balance sheets at March 31, 2021 and December 31, 2020 was as follows (in thousands): March 31, December 31, 2021 2020 Operating lease liabilities Current portion included in accrued expenses and other current liabilities $ 514 $ 492 Operating lease liabilities, net of current portion 44,827 42,773 Total operating lease liabilities $ 45,341 $ 43,265 The components of lease costs, which were included in operating expenses in the Company’s statements of operations and comprehensive loss were as follows (in thousands): Three Months Ended March 31, 2021 2020 Operating lease cost $ 1,734 $ 279 Variable cost 87 87 Total lease costs $ 1,821 $ 366 Variable costs included in the table above represent amounts the Company pays related to property taxes, insurance, maintenance and repair costs. Cash paid for amounts included in the measurement of the Company’s operating lease liabilities and presented within cash used in operating activities in the statements of cash flows was $0.3 million for the three months ended March 31, 2021 and 2020. Cash received for amounts related to tenant improvement allowances from lessors was $0.4 million and none for the three months ended March 31, 2021 and 2020, respectively. Operating Lease Obligations Future lease payments required under operating leases included on the Company’s balance sheet at March 31, 2021 are as follows (in thousands): Fiscal Year Ending December 31, 2021 (remaining 9 months) 2,083 2022 8,181 2023 8,427 2024 8,679 2025 8,940 Thereafter 53,246 Total future lease payments 89,556 Less: Present value adjustment 31,458 Present value of future lease incentives 12,757 Operating lease liabilities $ 45,341 Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, the Company used its incremental borrowing rate based on the information available at the lease commencement date. As of March 31, 2021, the weighted-average remaining lease term of the Company’s leases was 10.1 years and the weighted-average discount rate used to determine the operating lease liabilities included on its balance sheet was 8.8%. As of March 31, 2021, the Company is not party to any lease agreements containing material residual value guarantees or material restrictive covenants. Purchase Obligations The Company has entered into contractual agreements with various research and development organizations and suppliers in the normal course of its business. All contracts are terminable, with varying provisions regarding termination. If a contract were to be terminated, the Company would only be obligated for the products or services that the Company had received through the time of termination as well as any noncancelable minimum payments contractually agreed upon prior to the effective date of termination. In the case of terminating a clinical trial agreement with an investigational site conducting clinical activities on behalf of the Company, the Company would also be obligated to provide continued support for appropriate safety procedures through completion or termination of the associated study. At March 31, 2021, the Company had $196.4 million of noncancelable purchase obligations under these agreements. In-Licensing Agreements The Company has entered into exclusive and non-exclusive, royalty bearing license agreements with third-parties for certain intellectual property. Under the terms of the license agreements, the Company is obligated to pay milestone payments upon the achievement of specified clinical, regulatory and commercial milestones. Research and development expense associated with the Company’s milestone payments are recognized when such milestone has been achieved. Actual amounts due under the license agreements will vary depending on factors including, but not limited to, the number of products developed and the Company’s ability to further develop and commercialize the licensed products. The Company is also subject to future royalty payments based on sales of the licensed products. In-licensing payments to third-parties for milestones are recognized as research and development expense in the period of achievement. The Company did not recognize any milestone expense for the three months ended March 31, 2021 and 2020. As of March 31, 2021, the Company has not incurred any royalty liabilities related to its license agreements, as product sales have not yet commenced. Exclusive License Agreement with The Johns Hopkins University In December 2013, the Company entered into a license agreement with The Johns Hopkins University (“JHU”) for a worldwide exclusive license to develop, use, manufacture and commercialize covered product candidates including lirentelimab, which was amended in September 2016. Under the terms of the agreement, the Company has made upfront and milestone payments of $0.7 million through March 31, 2021 and may be required to make aggregate additional milestone payments of up to $1.8 million. The Company also issued 88,887 shares of common stock as consideration under the JHU license agreement. In addition to milestone payments, the Company is also subject to low single-digit royalties to JHU based on future net sales of each licensed therapeutic product candidate by the Company and its affiliates and sublicensees, with up to a low six-digit dollar minimum annual royalty payment. Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG In October 2013, the Company entered into a tripartite agreement with BioWa Inc. (“BioWa”), and Lonza Sales AG (“Lonza”), for the non-exclusive worldwide license to develop and commercialize product candidates including lirentelimab that are manufactured using a technology jointly developed and owned by BioWa and Lonza. Under the terms of the agreement, the Company has made milestone payments of $3.4 million through March 31, 2021 and may be required to make aggregate additional milestone payments of up to $38.0 million. In addition to milestone payments, the Company is also subject to minimum annual commercial license fees of $40,000 per year to BioWa until such time as BioWa receives royalty payments, as well as low single-digit royalties to BioWa and to Lonza. Royalties are based on future net sales by the Company and its affiliates and sublicensees and vary dependent on Lonza’s participation as sole manufacturer for commercial production. Indemnification Agreements The Company has entered into indemnification agreements with certain directors and officers that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. To date, no such matters have arisen and the Company does not believe that the outcome of any claims under indemnification arrangements will have a material adverse effect on its financial positions, results of operations or cash flows. Accordingly, the Company has not recorded a liability related to such indemnifications at March 31, 2021. Legal Contingencies On March 10, 2020, a putative securities class action complaint captioned Kim v. Allakos et al., No. 20-cv-01720 (N.D. Cal.) was filed in the United States District Court for the Northern District of California against the Company, its Chief Executive Officer, Dr. Robert Alexander, and its former Chief Financial Officer, Mr. Leo Redmond. The complaint asserts claims for violations of Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder and seeks damages based on alleged material misrepresentations and omissions concerning its Phase 2 clinical trials of lirentelimab. The proposed class period is August 5, 2019, through December 17, 2019, inclusive. On August 28, 2020, the plaintiff filed an amended complaint, adding as defendants Adam Tomasi, the Company’s President and Chief Operating Officer, and Henrik Rasmussen, the Company’s Chief Medical Officer. Given the early stage of this litigation matter, the Company cannot reasonably estimate a potential future loss or a range of potential future losses and has not recorded a contingent liability accrual as of March 31, 2021.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7. Stock-Based Compensation Total stock-based compensation expense recognized is as follows (in thousands): Three Months Ended March 31, 2021 2020 Research and development $ 5,063 $ 2,443 General and administrative 7,291 5,046 Total $ 12,354 $ 7,489 No income tax benefits for stock-based compensation expense have been recognized for the three months ended March 31, 2021 and 2020 as a result of the Company’s full valuation allowance applied to net deferred tax assets and net operating loss carryforwards. Equity Incentive Plans In July 2018, the Board of Directors adopted the 2018 Equity Incentive Plan (the “2018 Plan”). The 2018 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units (“RSUs”), stock appreciation rights and other stock-based awards. The Company initially reserved 4,000,000 shares of common stock for issuance under the 2018 Plan. The number of shares of common stock that may be issued under the 2018 Plan will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2019, equal to the least Following the IPO and upon the effectiveness of the 2018 Plan, the Company’s 2012 Equity Incentive Plan, as amended, (the “2012 Plan”), terminated and no further awards will be granted thereunder. All outstanding awards under the 2012 Plan will continue to be governed by their existing terms. Any shares subject to awards granted under the 2012 Plan that, on or after the termination of the 2012 Plan, expire or terminate and shares previously issued pursuant to awards granted under the 2012 Plan that, on or after the termination of the 2012 Plan, are forfeited or repurchased by the Company will be transferred into the 2018 Plan. As of March 31, 2021, the maximum number of shares that may be added to the 2018 Plan pursuant to the preceding clause is 4,432,472 shares. Prior to its termination, the 2012 Plan provided for the grant of stock options, stock appreciation rights, restricted stock and restricted stock units to employees, directors and consultants. Stock options granted under the 2012 Plan generally vest over four years and expire no more than 10 years from the date of grant. Stock Options The following weighted-average assumptions were used to calculate the fair value of stock options granted during the periods indicated: Three Months Ended March 31, 2021 2020 Risk-free interest rate 0.77 % 1.10 % Expected volatility 69.57 % 68.17 % Expected dividend yield — — Expected term (in years) 6.06 6.08 The Company’s stock option activity during the three months ended March 31, 2021 is summarized as follows (number of shares in thousands): Weighted- Average Options Exercise Outstanding Price Balance at December 31, 2020 6,616 $ 15.53 Granted 56 $ 128.38 Exercised (321 ) $ 11.80 Forfeited (100 ) $ 29.00 Balance at March 31, 2021 6,251 $ 16.53 Options exercisable 4,753 $ 9.51 Options vested and expected to vest 6,236 $ 16.43 During the three months ended March 31, 2021 and 2020, the Company did not grant any stock options with performance-based or market-based vesting conditions. As of March 31, 2021, total unrecognized stock-based compensation expense relating to unvested stock options was $31.9 million. This amount is expected to be recognized over a weighted-average period of 2.4 years. Restricted Stock Units RSU activity under the 2018 Plan during the three months ended March 31, 2021 is summarized as follows (in thousands, except per share data): Weighted- Average Grant Date Shares Fair Value Balance at December 31, 2020 1,161 $ 102.24 Granted 32 $ 127.96 Vested (38 ) $ 89.95 Forfeited (62 ) $ 99.08 Balance at March 31, 2021 1,093 $ 103.61 The weighted-average fair value of RSUs granted during the three months ended March 31, 2021 and 2020 was $127.96 and $67.57, respectively. As of March 31 , 2021, total unrecognized stock-based compensation expense relating to unvested RSUs was $103.4 million and the weighted-average remaining vesting period was 3.4 years. 2018 Employee Stock Purchase Plan In July 2018, the Company’s Board of Directors and stockholders approved the 2018 Employee Stock Purchase Plan (the “2018 ESPP”). There were 500,000 shares of common stock initially reserved for issuance under the 2018 ESPP. The number of shares of common stock that may be issued under the 2018 ESPP shall automatically increase on each January 1, beginning with the fiscal year ending December 31, 2019, equal to the least of (i) 1,000,000 shares, (ii) 1% of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year and (iii) such other amount determined by the 2018 ESPP administrator. Under the 2018 ESPP, employees may purchase shares of the Company’s common stock at a price per share equal to 85% of the lower of the fair market value of the common stock on the first trading day of the offering period or on the exercise date. The 2018 ESPP provides for consecutive, overlapping 24-month offering periods, each of which will include four 6-month purchase periods.

Defined Contribution Plans

Defined Contribution Plans	3 Months Ended
	Mar. 31, 2021
Compensation And Retirement Disclosure [Abstract]
Defined Contribution Plans	8. Defined Contribution Plans In January 2018, the Company established a defined contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) plan”). The 401(k) plan covers all employees who meet defined minimum age and service requirements. Employee contributions are voluntary and are determined on an individual basis, limited to the maximum amount allowable under U.S. federal tax regulations. The Company makes matching contributions of up to 4% of the eligible employees’ compensation to the 401(k) plan. During each of the three months ended March 31, 2021 and 2020, the Company made contributions to the 401(k) plan of $0.2 million

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited interim financial statements have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts and disclosures reported in the financial statements and accompanying notes. The interim balance sheet as of March 31, 2021, the statements of operations and comprehensive loss, statements of stockholders’ equity and statements of cash flows for the three months ended March 31, 2021 and 2020 are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair presentation of the Company’s financial position as of March 31, 2021 and its results of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 and its cash flows for the three months ended March 31, 2021 and 2020. Certain information and note disclosures normally included in annual audited financial statements prepared in accordance with U.S. GAAP have been omitted. The financial data and the other financial information disclosed in these notes to the interim financial statements are also unaudited. The results of operations for any interim period are not necessarily indicative of the results to be expected for the entire year or for any other future annual or interim period. The balance sheet as of March 31, 2021 included herein was derived from the audited financial statements as of that date. These interim financial statements should be read in conjunction with the Company’s audited financial statements included in the Company’s Annual Report on Form 10-K, which was filed with the Securities and Exchange Commission (the “SEC”) on March 1, 2021.
Use of Estimates	Use of Estimates Management uses significant judgment when making estimates related to common stock valuation and related stock-based compensation expense, accrued research and development expense, and deferred tax valuation allowances. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates under different assumptions or conditions, and those differences could be material to the financial position and results of operations.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to credit risk principally consist of cash, cash equivalents and marketable securities. These financial instruments are held in accounts at a single financial institution that management believes possesses high credit quality. Amounts on deposit with this financial institution have and will continue to exceed federally-insured limits. The Company has not experienced any losses on its cash deposits. Additionally, the Company’s investment policy limits its investments to certain types of securities issued by or backed by the U.S. government and its agencies. The Company is subject to a number of risks similar to that of other clinical stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of current or future clinical trials, its reliance on third-parties to conduct its clinical trials, the need to obtain regulatory and marketing approvals for its product candidates, competitive developments, the need to successfully commercialize and gain market acceptance of the Company’s product candidates, its right to develop and commercialize its product candidates pursuant to the terms and conditions of the licenses granted to the Company, protection of proprietary technology, the ability to make milestone, royalty or other payments due under licensing agreements, and the need to secure and maintain adequate manufacturing arrangements with third-parties. If the Company does not successfully commercialize or partner its product candidates, it will be unable to generate product revenue or achieve profitability.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the accompanying statements of cash flows (in thousands): March 31, December 31, 2021 2020 Cash and cash equivalents $ 169,989 $ 207,177 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 172,264 $ 209,452 March 31, December 31, 2020 2019 Cash and cash equivalents $ 135,942 $ 38,367 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 138,217 $ 40,642 Restricted cash at March 31, 2021 represents $2.3 million in deposits for the lease of the Company’s facilities in Redwood City, California and San Carlos, California. Both security deposits are in the form of letters of credit secured by restricted cash. Restricted cash amounts are included within other long-term assets on the Company’s balance sheets.
Marketable Securities	Marketable Securities The Company invests in marketable securities, primarily securities issued by the United States government and its agencies. The Company’s marketable securities are considered available-for-sale and are classified as current assets even when the stated maturities of the underlying securities exceed one year from the date of the current balance sheet being reported. This classification reflects management’s ability and intent to utilize proceeds from the sale of such investments to fund ongoing operations. Unrealized gains and losses are excluded from earnings and are reported as a component of accumulated other comprehensive gain. The cost of securities sold is determined using the specific-identification method. Interest earned and adjustments for the amortization of premiums and discounts on investments are included in interest income, net, on the statements of operations and comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on investments in marketable securities are included in other expense, net, on the statements of operations and comprehensive loss.
Operating Leases	Operating Leases Effective January 1, 2019, the Company accounts for its leases in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 842, “Leases” (“ASC 842”). As part of this transition, the Company elected a number of optional practical expedients made available under the ASC 842 transition guidance including (i) carrying forward the Company’s historical lease classifications, (ii) foregoing of re-evaluation of historical contracts using ASC 842’s definition of a lease, (iii) foregoing a re-assessment of initial direct costs related to leases that existed prior to adoption, (iv) combining lease and non-lease components for all classes of assets, and (v) recognizing lease expense for all contracts with an initial term of 12 months or less within the statements of operations and comprehensive loss on a straight-line basis over the requisite lease term. Under ASC 842, the Company accounts for its leases by recording right-of-use assets and lease liabilities on the balance sheets. Right-of-use assets represent the Company’s right to use an underlying asset over the lease term and include any lease payments made prior to the lease commencement date and are reduced by lease incentives. Lease liabilities represent the present value of the total lease payments over the lease term, calculated using the Company’s incremental borrowing rate. In determining the Company’s incremental borrowing rate, consideration is given to the term of the lease and the Company’s credit risk. The Company recognizes options to extend a lease when it is reasonably certain that it will exercise such extension. The Company does not recognize options to terminate a lease when it is reasonably certain that it will not exercise such early termination options. Lease expense is recognized on a straight-line basis over the expected lease term. Prior to the Company’s adoption of ASC 842, the Company accounted for its leases in accordance with FASB ASC 840, Leases (“ASC 840”). Under ASC 840, r ent expense is recorded on a straight-line basis over the term of the lease. Differences that exist between cash rent payments and the recognition of rent expense, such as those resulting from rent abatements or contractual escalations of future lease payments, are recorded as a deferred rent liability and recognized as adjustments to rental expense on a straight-line basis over the term of the lease. The current portion of the deferred rent liability is included within accrued expenses and other current liabilities on the Company’s balance sheet s with remainder included within operating lease liabilities, net of current portion . Tenant improvement allowances received are recorded as lease incentive obligations included in accrued expenses and other current liabilities and operating lease liabilities , net of current portion on the Company’s balance sheets and amortized to rent expense over the term of the lease .
Accrued Research and Development Expense	Accrued Research and Development Expense Service agreements with contract development and manufacturing organizations (“CDMOs”), clinical contract research organizations (“CROs”) and clinical investigative sites comprise a significant component of the Company’s research and development activities. External costs for these vendors are recognized as the services are incurred. The Company accrues for expenses resulting from obligations under agreements with its third-parties for which the timing of payments does not match the periods over which the materials or services are provided to the Company. Accruals are recorded based on estimates of services received and efforts expended pursuant to agreements established with CDMOs, clinical CROs, clinical investigative sites and other outside service providers. These estimates are typically based on contracted amounts applied to the proportion of work performed and determined through analysis with internal personnel and external service providers as to the progress or stage of completion of the services. The Company makes judgements and estimates in determining the accrual balance in each reporting period. In the event advance payments are made to a CDMO, clinical CRO, clinical investigative site or other outside service provider, the payments are recorded within prepaid expenses and other current assets and subsequently recognized as research and development expense when the associated services have been performed. As actual costs become known, the Company adjusts its liabilities and assets. Inputs, such as the extent of services received and the duration of services to be performed, may vary from the Company’s estimates, which will result in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. The Company’s historical estimates have not been materially different from actual amounts recorded .
Research and Development Expense	Research and Development Expense Research and development costs are expensed as incurred. Research and development costs include, among others, consulting costs, salaries, benefits, travel, stock-based compensation, laboratory supplies and other non-capital equipment utilized for in-house research, allocation of facilities and overhead costs and external costs paid to third-parties that conduct research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements, including milestone payments, are also included in research and development expense. Advance payments for goods or services to be rendered in the future for use in research and development activities are deferred and included in prepaid expenses and other current assets. The deferred amounts are expensed as the related goods are delivered or the services are performed.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in stockholders’ equity (deficit) during a period from transactions and other events and circumstances from non-owner sources. The difference between net loss and comprehensive loss for the three months ended March 31, 2021 and 2020 are a result of unrealized gains and losses on the Company’s investments in marketable securities included in current assets on the balance sheets.
Net Loss per Share	Net Loss per Share The Company calculates basic net loss per share by dividing the net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. The Company calculates diluted net loss per share after giving consideration to all potentially dilutive securities outstanding during the period using the treasury-stock and if-converted methods, except where the effect of including such securities would be Basic and diluted net loss per share was calculated as follows (in thousands, except per share data): Three Months Ended March 31, 2021 2020 Numerator: Net loss $ (55,558 ) $ (27,824 ) Denominator: Weighted-average shares of common stock outstanding, basic and diluted 53,186 48,691 Net loss per share, basic and diluted $ (1.04 ) $ (0.57 ) The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect for the periods indicated (in thousands): Three Months Ended March 31, 2021 2020 Options to purchase common stock 6,251 7,105 Unvested restricted stock units 1,093 572 Shares issuable under employee stock purchase plans 4 8 Total 7,348 7,685
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and Adopted Accounting Pronouncements The Company has reviewed recently issued accounting pronouncements and concluded they are either not applicable to the business or that no material effect is expected on the Company’s financial statements as a result of future adoption.
Impact of Recent Legislation	Impact of Recent Legislation In March 2020, the Coronavirus Aid, Relief and Economic Security Act (“the CARES Act”) was signed into law. The CARES Act includes provisions relating to several aspects of corporate income taxes. The Company does not currently expect the CARES Act to have a material impact on its income tax positions; however, it will continue to monitor the provisions of the CARES Act in relation to its operations .

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the accompanying statements of cash flows (in thousands): March 31, December 31, 2021 2020 Cash and cash equivalents $ 169,989 $ 207,177 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 172,264 $ 209,452 March 31, December 31, 2020 2019 Cash and cash equivalents $ 135,942 $ 38,367 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 138,217 $ 40,642
Calculation of Basic and Diluted Net Loss per Share	Basic and diluted net loss per share was calculated as follows (in thousands, except per share data): Three Months Ended March 31, 2021 2020 Numerator: Net loss $ (55,558 ) $ (27,824 ) Denominator: Weighted-average shares of common stock outstanding, basic and diluted 53,186 48,691 Net loss per share, basic and diluted $ (1.04 ) $ (0.57 )
Summary of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share	The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect for the periods indicated (in thousands): Three Months Ended March 31, 2021 2020 Options to purchase common stock 6,251 7,105 Unvested restricted stock units 1,093 572 Shares issuable under employee stock purchase plans 4 8 Total 7,348 7,685

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The Company’s financial assets measured at fair value on a recurring basis were as follows (in thousands): March 31, 2021 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 168,754 $ — $ — $ 168,754 Total cash equivalents 168,754 — — 168,754 Short-term marketable securities U.S. treasuries 445,945 — — 445,945 Total short-term marketable securities 445,945 — — 445,945 Total cash equivalents and short-term marketable securities $ 614,699 $ — $ — $ 614,699 December 31, 2020 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 205,408 $ — $ — $ 205,408 Total cash equivalents 205,408 — — 205,408 Short-term marketable securities U.S. treasuries 451,820 — — 451,820 Total short-term marketable securities 451,820 — — 451,820 Total cash equivalents and short-term marketable securities $ 657,228 $ — $ — $ 657,228

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2021
Investments Debt And Equity Securities [Abstract]
Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Marketable Securities	The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type at March 31, 2021 and December 31, 2020 are summarized in the table below (in thousands): March 31, 2021 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Available-for-sale securities U.S. treasuries classified as investments $ 445,857 $ 88 $ — $ 445,945 Total available-for-sale securities $ 445,857 $ 88 $ — $ 445,945 December 31, 2020 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Available-for-sale securities U.S. treasuries classified as investments $ 451,812 $ 26 $ (18 ) $ 451,820 Total available-for-sale securities $ 451,812 $ 26 $ (18 ) $ 451,820

Balance Sheet Components and _2

Balance Sheet Components and Supplemental Disclosures (Tables)	3 Months Ended
	Mar. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net, consisted of the following (in thousands): March 31, December 31, 2021 2020 Laboratory equipment $ 4,232 $ 4,236 Furniture and office equipment 1,784 1,784 Leasehold improvements 4,581 4,581 Construction-in-progress 6,964 1,325 17,561 11,926 Less accumulated depreciation (3,941 ) (3,581 ) Property and equipment, net $ 13,620 $ 8,345
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): March 31, December 31, 2021 2020 Accrued contract research and development expense $ 8,091 $ 4,697 Accrued compensation and benefits expense 3,798 3,214 Current portion of operating lease liabilities 514 492 Other current liabilities 573 87 Total $ 12,976 $ 8,490

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Summary of Classification of Company's Operating Lease Liabilities	Classification of the Company’s operating lease liabilities included on its balance sheets at March 31, 2021 and December 31, 2020 was as follows (in thousands): March 31, December 31, 2021 2020 Operating lease liabilities Current portion included in accrued expenses and other current liabilities $ 514 $ 492 Operating lease liabilities, net of current portion 44,827 42,773 Total operating lease liabilities $ 45,341 $ 43,265
Summary of Components of Lease Costs	The components of lease costs, which were included in operating expenses in the Company’s statements of operations and comprehensive loss were as follows (in thousands): Three Months Ended March 31, 2021 2020 Operating lease cost $ 1,734 $ 279 Variable cost 87 87 Total lease costs $ 1,821 $ 366
Summary of Future Lease Payments Required Under Operating Leases	Future lease payments required under operating leases included on the Company’s balance sheet at March 31, 2021 are as follows (in thousands): Fiscal Year Ending December 31, 2021 (remaining 9 months) 2,083 2022 8,181 2023 8,427 2024 8,679 2025 8,940 Thereafter 53,246 Total future lease payments 89,556 Less: Present value adjustment 31,458 Present value of future lease incentives 12,757 Operating lease liabilities $ 45,341

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Total Stock-Based Compensation Expense Recognized	Total stock-based compensation expense recognized is as follows (in thousands): Three Months Ended March 31, 2021 2020 Research and development $ 5,063 $ 2,443 General and administrative 7,291 5,046 Total $ 12,354 $ 7,489
Summary of Weighted-Average Assumptions Used to Calculate Fair Value of Stock Options Granted	The following weighted-average assumptions were used to calculate the fair value of stock options granted during the periods indicated: Three Months Ended March 31, 2021 2020 Risk-free interest rate 0.77 % 1.10 % Expected volatility 69.57 % 68.17 % Expected dividend yield — — Expected term (in years) 6.06 6.08
Summary of Stock Option Activity	The Company’s stock option activity during the three months ended March 31, 2021 is summarized as follows (number of shares in thousands): Weighted- Average Options Exercise Outstanding Price Balance at December 31, 2020 6,616 $ 15.53 Granted 56 $ 128.38 Exercised (321 ) $ 11.80 Forfeited (100 ) $ 29.00 Balance at March 31, 2021 6,251 $ 16.53 Options exercisable 4,753 $ 9.51 Options vested and expected to vest 6,236 $ 16.43
Summary of Restricted Stock Awards and Restricted Stock Units	RSU activity under the 2018 Plan during the three months ended March 31, 2021 is summarized as follows (in thousands, except per share data): Weighted- Average Grant Date Shares Fair Value Balance at December 31, 2020 1,161 $ 102.24 Granted 32 $ 127.96 Vested (38 ) $ 89.95 Forfeited (62 ) $ 99.08 Balance at March 31, 2021 1,093 $ 103.61

Organization and Business - Add

Organization and Business - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Net loss	$ 55,558	$ 27,824
Cash used in operations	46,259	$ 18,614
Accumulated deficit	398,522		$ 342,964
Cash, cash equivalents and marketable securities	$ 615,900

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 169,989	$ 207,177	$ 135,942	$ 38,367
Restricted cash in other long-term assets, deposit for lease facility	2,275	2,275	2,275	2,275
Total cash, cash equivalents and restricted cash	$ 172,264	$ 209,452	$ 138,217	$ 40,642

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Restricted cash in other long term assets, deposit for lease facility	$ 2,275	$ 2,275	$ 2,275	$ 2,275

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net loss	$ (55,558)	$ (27,824)
Weighted-average number of common shares outstanding:
Weighted-average shares of common stock outstanding, basic and diluted	53,186	48,691
Net loss per share, basic and diluted	$ (1.04)	$ (0.57)

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	7,348	7,685
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	6,251	7,105
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	1,093	572
Shares Issuable under Employee Stock Purchase Plans
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	4	8

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	$ 445,945	$ 451,820
Fair Value, Measurements, Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	168,754	205,408
Short-term marketable securities	445,945	451,820
Total cash equivalents and short-term marketable securities	614,699	657,228
Fair Value, Measurements, Recurring Basis | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	168,754	205,408
Short-term marketable securities	445,945	451,820
Total cash equivalents and short-term marketable securities	614,699	657,228
Fair Value, Measurements, Recurring Basis | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term marketable securities	0	0
Total cash equivalents and short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term marketable securities	0	0
Total cash equivalents and short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	168,754	205,408
Fair Value, Measurements, Recurring Basis | Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	168,754	205,408
Fair Value, Measurements, Recurring Basis | Money Market Funds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring Basis | Money Market Funds | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring Basis | U.S. Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	445,945	451,820
Fair Value, Measurements, Recurring Basis | U.S. Treasuries | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	445,945	451,820
Fair Value, Measurements, Recurring Basis | U.S. Treasuries | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis | U.S. Treasuries | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	$ 0	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Transfers of assets between level 1 to level 2	$ 0	$ 0
Transfers of assets between level 2 to level 1	0	0
Transfers of liabilities between level 1 to level 2	0	0
Transfers of liabilities between level 2 to level 1	0	0
Transfers of assets into level 3	0	0
Transfers of assets out of level 3	0	0
Transfers of liabilities into level 3	0	0
Transfers of liabilities out of level 3	$ 0	$ 0

Marketable Securities - Marketa

Marketable Securities - Marketable Securities - Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 445,857	$ 451,812
Unrealized Gains	88	26
Unrealized Losses	0	(18)
Fair Value	445,945	451,820
U.S. Treasuries | Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	445,857	451,812
Unrealized Gains	88	26
Unrealized Losses	0	(18)
Fair Value	$ 445,945	$ 451,820

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities in an unrealized loss position, fair value	$ 0		$ 91,400,000
Available for sale securities gross recognized gains on sale or maturity	0	$ 0
Available for sale securities gross recognized losses on sale or maturity	$ 0	$ 0
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, remaining maturity period	1 year		1 year

Balance Sheet Components and _3

Balance Sheet Components and Supplemental Disclosures - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 17,561	$ 11,926
Less accumulated depreciation	(3,941)	(3,581)
Property and equipment, net	13,620	8,345
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,232	4,236
Furniture And Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,784	1,784
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,581	4,581
Construction In Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 6,964	$ 1,325

Balance Sheet Components and _4

Balance Sheet Components and Supplemental Disclosures - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization	$ 372	$ 393

Balance Sheet Components and _5

Balance Sheet Components and Supplemental Disclosures - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued contract research and development expense	$ 8,091	$ 4,697
Accrued compensation and benefits expense	3,798	3,214
Current portion of operating lease liabilities	514	492
Other current liabilities	573	87
Total	$ 12,976	$ 8,490

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended		3 Months Ended		87 Months Ended	89 Months Ended
	Dec. 31, 2019USD ($)ft²	Jan. 31, 2018USD ($)ft²	Mar. 31, 2021USD ($)shares	Mar. 31, 2020USD ($)	Mar. 31, 2021USD ($)shares	Mar. 31, 2021USD ($)shares	Dec. 31, 2020shares	Dec. 31, 2013shares
Commitments And Contingencies [Line Items]
Cash paid for amounts included in measurement of operating lease liabilities			$ 300,000	$ 300,000
Cash received for amounts related to tenant improvement allowances from lessors			$ 400,000	0
Operating lease, weighted-average remaining lease term			10 years 1 month 6 days		10 years 1 month 6 days	10 years 1 month 6 days
Operating lease, weighted-average discount rate			8.80%		8.80%	8.80%
Non-cancelable purchase obligations			$ 196,400,000		$ 196,400,000	$ 196,400,000
Common stock, shares issued | shares			53,457,000		53,457,000	53,457,000	53,081,000
In-Licensing Agreements
Commitments And Contingencies [Line Items]
Milestone expense			$ 0	$ 0
Accrued Royalties			0		$ 0	$ 0
Exclusive License Agreement with The Johns Hopkins University
Commitments And Contingencies [Line Items]
Upfront and milestone payments					700,000
Common stock, shares issued | shares								88,887
Exclusive License Agreement with The Johns Hopkins University | Maximum
Commitments And Contingencies [Line Items]
Aggregate additional milestone payments					1,800,000
Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG
Commitments And Contingencies [Line Items]
Milestone payments						3,400,000
Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG | Maximum
Commitments And Contingencies [Line Items]
Aggregate additional milestone payments						38,000,000
Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG | Minimum [Member]
Commitments And Contingencies [Line Items]
Annual commercial license fees						40,000
2019 San Carlos Lease Agreement
Commitments And Contingencies [Line Items]
Operating lease agreement initiation period	2019-12
Base term of lease	10 years 3 months
Lessee operating lease expected termination Period	2031-09
Lease term extension period	5 years
Area of office and laboratory space | ft²	98,000
Contractual tenant improvement allowance	$ 14,700,000
Security deposit in the form of letter of credit secured by restricted cash			1,500,000		1,500,000	1,500,000
2018 Redwood City Lease Agreement
Commitments And Contingencies [Line Items]
Operating lease agreement initiation period		2018-01
Base term of lease		10 years 9 months
Lessee operating lease expected termination Period		2029-07
Lease term extension period		5 years
Area of office and laboratory space | ft²		25,000
Tenant improvement allowance		$ 1,400,000
Security deposit in the form of letter of credit secured by restricted cash			$ 800,000		$ 800,000	$ 800,000

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Classification of Company's Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Operating lease liabilities
Current portion included in accrued expenses and other current liabilities	$ 514	$ 492
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued expenses and other current liabilities	Accrued expenses and other current liabilities
Operating lease liabilities, net of current portion	$ 44,827	$ 42,773
Total operating lease liabilities	$ 45,341	$ 43,265

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Components of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating lease cost	$ 1,734	$ 279
Variable cost	87	87
Total lease costs	$ 1,821	$ 366

Commitments and Contingencies_4

Commitments and Contingencies - Summary of Future Lease Payments Required Under Operating Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Operating Lease Liabilities Payments Due [Abstract]
2021 (remaining 9 months)	$ 2,083
2022	8,181
2023	8,427
2024	8,679
2025	8,940
Thereafter	53,246
Total future lease payments	89,556
Present value adjustment	31,458
Present value of future lease incentives	12,757
Operating lease liabilities	$ 45,341	$ 43,265

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Total Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 12,354	$ 7,489
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	5,063	2,443
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 7,291	$ 5,046

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended
	Jul. 31, 2018	Mar. 31, 2021	Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Tax benefits for stock-based compensation expense recognized		$ 0	$ 0
Stock options granted		56,000
Total unrecognized stock-based compensation expense relating to unvested stock options		$ 31,900,000
Total stock-based compensation expense		$ 12,354,000	$ 7,489,000
Performance-Based Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted		0	0
Market-Based Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted		0	0
Exercise of Common Stock Options Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average recognition period		2 years 4 months 24 days
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average recognition period		3 years 4 months 24 days
Weighted-average fair value of RSUs granted		$ 127.96	$ 67.57
Total unrecognized stock-based compensation expense		$ 103,400,000
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance	500,000
Increase in number of common stock shares reserved for issuance per year	1,000,000
Percentage increase in shares reserved for issuance per year	1.00%
Price as a percentage of fair market value of common stock	85.00%
Consecutive overlapping offering period	24 months
First offering period commence date		Jul. 18, 2018
Total stock-based compensation expense		$ 200,000	$ 200,000
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance	4,000,000
Increase in number of common stock shares reserved for issuance per year	5,000,000
Percentage increase in shares reserved for issuance per year	5.00%
Award vesting period	4 years
Maximum number of additional shares authorized to be added to the Plan		4,432,472
2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option expiration period	10 years

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used to Calculate Fair Value of Stock Options Granted (Details) - Employees and Non-Employees - Exercise of Common Stock Options Outstanding	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.77%	1.10%
Expected volatility	69.57%	68.17%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	6 years 21 days	6 years 29 days

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock Option Activity (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Beginning balance | shares	6,616
Options Outstanding, Granted | shares	56
Options Outstanding, Exercised | shares	(321)
Options Outstanding, forfeited | shares	(100)
Options Outstanding, Ending balance | shares	6,251
Options Outstanding, Options exercisable | shares	4,753
Options Outstanding, Options vested and expected to vest | shares	6,236
Weighted Average Exercise Price, Beginning balance | $ / shares	$ 15.53
Weighted Average Exercise Price, Granted | $ / shares	128.38
Weighted Average Exercise Price, Exercised | $ / shares	11.80
Weighted Average Exercise Price, Forfeited | $ / shares	29
Weighted Average Exercise Price, Ending balance | $ / shares	16.53
Weighted Average Exercise Price, Options exercisable | $ / shares	9.51
Weighted Average Exercise Price, Options vested and expected to vest | $ / shares	$ 16.43

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of RSU Activity Under 2018 Plan (Details) - Restricted Stock Units - $ / shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Number of Shares
Balance at December 31, 2020	1,161
Granted	32
Vested	(38)
Forfeited	(62)
Balance at March 31, 2021	1,093
Weighted-Average Grant Date Fair Value
Balance at December 31, 2020	$ 102.24
Granted	127.96	$ 67.57
Vested	89.95
Forfeited	99.08
Balance at March 31, 2021	$ 103.61

Defined Contribution Plans - Ad

Defined Contribution Plans - Additional Information (Details) - 401(K) Plan - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Contribution Plan Disclosure [Line Items]
Employer contribution matching percentage	4.00%	4.00%
Contributions made by employer	$ 0.2	$ 0.2