Allakos (ALLK) 10-Q 10 Aug 20 2020 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Aug. 05, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
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		48,913,669
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	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 153,898	$ 38,367
Investments in marketable securities	301,048	457,534
Prepaid expenses and other current assets	3,336	3,969
Total current assets	458,282	499,870
Property and equipment, net	7,703	8,410
Operating lease right-of-use assets	5,633	5,775
Other long-term assets	2,839	2,839
Total assets	474,457	516,894
Current liabilities:
Accounts payable	9,617	5,963
Accrued expenses and other current liabilities	9,962	7,098
Total current liabilities	19,579	13,061
Other long-term liabilities	7,875	8,112
Total liabilities	27,454	21,173
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock, $0.001 par value per share; 20,000 shares authorized as of June 30, 2020 and December 31, 2019; no shares issued and outstanding as of June 30, 2020 and December 31, 2019	0	0
Common stock, $0.001 par value per share; 200,000 shares authorized as of June 30, 2020 and December 31, 2019; 48,913 and 48,668 shares issued and outstanding as of June 30, 2020 and December 31, 2019, respectively	49	48
Additional paid-in capital	702,767	685,020
Accumulated other comprehensive gain	787	137
Accumulated deficit	(256,600)	(189,484)
Total stockholders’ equity	447,003	495,721
Total liabilities and stockholders’ equity	$ 474,457	$ 516,894

BALANCE SHEETS (Unaudited) (Par

BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	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	48,913,000	48,668,000
Common stock, shares outstanding	48,913,000	48,668,000

STATEMENTS OF OPERATIONS AND CO

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses
Research and development	$ 28,346	$ 14,111	$ 46,631	$ 29,209
General and administrative	12,058	5,946	23,646	11,775
Total operating expenses	40,404	20,057	70,277	40,984
Loss from operations	(40,404)	(20,057)	(70,277)	(40,984)
Interest income, net	1,284	971	3,273	2,001
Other income (expense), net	(172)	14	(112)	(42)
Net loss	(39,292)	(19,072)	(67,116)	(39,025)
Unrealized gain (loss) on marketable securities, net of tax	(1,219)	84	650	129
Comprehensive loss	$ (40,511)	$ (18,988)	$ (66,466)	$ (38,896)
Net loss per common share:
Basic and diluted	$ (0.80)	$ (0.44)	$ (1.38)	$ (0.91)
Weighted-average number of common shares outstanding:
Basic and diluted	48,816	43,115	48,753	42,868

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 (Loss)	Accumulated Deficit
Balance at Dec. 31, 2018	$ 183,994	$ 42	$ 288,079	$ (15)	$ (104,112)
Balance, Shares at Dec. 31, 2018		42,117
Stock-based compensation expense	2,834	$ 0	2,834	0	0
Issuance of common stock upon exercise of stock options	368	$ 1	367	0	0
Issuance of common stock upon exercise of stock options, Shares		968
Issuance of common stock upon 2018 ESPP purchase	595	$ 0	595	0	0
Issuance of common stock upon 2018 ESPP purchase, Shares		39
Vesting of restricted common stock	6	$ 0	6	0	0
Unrealized gain (loss) on marketable securities	45	0	0	45	0
Net loss	(19,953)	0	0	0	(19,953)
Balance at Mar. 31, 2019	167,889	$ 43	291,881	30	(124,065)
Balance, Shares at Mar. 31, 2019		43,124
Balance at Dec. 31, 2018	183,994	$ 42	288,079	(15)	(104,112)
Balance, Shares at Dec. 31, 2018		42,117
Unrealized gain (loss) on marketable securities	129
Net loss	(39,025)
Balance at Jun. 30, 2019	152,150	$ 43	295,130	114	(143,137)
Balance, Shares at Jun. 30, 2019		43,184
Balance at Mar. 31, 2019	167,889	$ 43	291,881	30	(124,065)
Balance, Shares at Mar. 31, 2019		43,124
Stock-based compensation expense	3,105	$ 0	3,105	0	0
Issuance of common stock upon exercise of stock options	138	$ 0	138	0	0
Issuance of common stock upon exercise of stock options, Shares		60
Vesting of restricted common stock	6	$ 0	6	0	0
Unrealized gain (loss) on marketable securities	84	0	0	84	0
Net loss	(19,072)	0	0	0	(19,072)
Balance at Jun. 30, 2019	152,150	$ 43	295,130	114	(143,137)
Balance, Shares at Jun. 30, 2019		43,184
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 (loss) 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, 2019	$ 495,721	$ 48	685,020	137	(189,484)
Balance, Shares at Dec. 31, 2019		48,668
Issuance of common stock upon exercise of stock options, Shares	205
Unrealized gain (loss) on marketable securities	$ 650
Net loss	(67,116)
Balance at Jun. 30, 2020	447,003	$ 49	702,767	787	(256,600)
Balance, Shares at Jun. 30, 2020		48,913
Balance at Mar. 31, 2020	478,044	$ 48	693,298	2,006	(217,308)
Balance, Shares at Mar. 31, 2020		48,765
Stock-based compensation expense	7,762	$ 0	7,762	0	0
Issuance of common stock upon exercise of stock options	1,708	$ 1	1,707	0	0
Issuance of common stock upon exercise of stock options, Shares		148
Unrealized gain (loss) on marketable securities	(1,219)	$ 0	0	(1,219)	0
Net loss	(39,292)	0	0	0	(39,292)
Balance at Jun. 30, 2020	$ 447,003	$ 49	$ 702,767	$ 787	$ (256,600)
Balance, Shares at Jun. 30, 2020		48,913

STATEMENTS OF CASH FLOWS (unaud

STATEMENTS OF CASH FLOWS (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (67,116)	$ (39,025)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	777	732
Stock-based compensation	15,251	5,939
Net amortization of premiums and discounts on marketable securities	966	(1,330)
Noncash lease expense	142	142
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	13	1,508
Accounts payable	3,654	874
Accrued expenses and other current liabilities	2,627	3,314
Other long-term liabilities	0	144
Net cash used in operating activities	(43,686)	(27,702)
Cash flows from investing activities
Purchases of marketable securities	(90,010)	(115,984)
Proceeds from maturities of marketable securities	246,800	146,000
Purchases of property and equipment	(70)	(618)
Net cash provided by investing activities	156,720	29,398
Cash flows from financing activities
Proceeds from exercise of stock options	1,741	506
Proceeds from issuance of common stock under the 2018 ESPP	756	595
Net cash provided by financing activities	2,497	1,101
Net increase in cash, cash equivalents and restricted cash	115,531	2,797
Cash, cash equivalents and restricted cash, beginning of period	40,642	34,462
Cash, cash equivalents and restricted cash, end of period	156,173	37,259
Noncash investing and financing items:
Right-of-use assets obtained in exchange for lease obligations	0	6,050
Vesting of restricted common stock subject to repurchase	$ 0	$ 12

Organization and Business

Organization and Business	6 Months Ended
	Jun. 30, 2020
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 six months ended June 30, 2020, the Company incurred a net loss of $67.1 million and used $43.7 million of cash in operations. At June 30, 2020, the Company had an accumulated deficit of $256.6 million and does not expect to experience positive cash flows from operating activities in the foreseeable future. The Company has financed its operations to date primarily through the sale of common stock and issuance of convertible preferred stock. Management expects to incur additional operating losses in the future as the Company continues to further develop, seek regulatory approval for and, if approved, commence commercialization of its product candidates. The Company had $454.9 million of cash, cash equivalents and marketable securities at June 30, 2020. Management believes that this amount is sufficient to fund the Company’s operations for at least the next 12 months from the issuance date of these financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
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 June 30, 2020, the statements of operations and comprehensive loss, statements of stockholders’ equity and statements of cash flows for the three and six months ended June 30, 2020 and 2019 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 June 30, 2020 and its results of operations and comprehensive loss for the three and six months ended June 30, 2020 and 2019 and its cash flows for the six months ended June 30, 2020 and 2019. 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 December 31, 2019 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 February 25, 2020. Use of Estimates Management uses significant judgment when making estimates related to common stock valuation and related stock-based compensation expense, accrued expenses related to clinical trials, calculation of right-of-use assets and lease liabilities, 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. Restricted cash as of June 30, 2020 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. 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): June 30, December 31, 2020 2019 Cash and cash equivalents $ 153,898 $ 38,367 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 156,173 $ 40,642 June 30, December 31, 2019 2018 Cash and cash equivalents $ 36,457 $ 33,660 Restricted cash in other long-term assets, deposit for lease facility 802 802 Total cash, cash equivalents and restricted cash $ 37,259 $ 34,462 Marketable Securities The Company invests in marketable securities, primarily securities issued by the U.S. 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. 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 the fair value of an available-for-sale security due to a credit loss are included in other expense, net, on the statements of operations and comprehensive loss to the extent the Company does not expect to recover the amortized cost basis. Any portion of a decline in fair value that is due to factors other than a credit loss is excluded from earnings and reported as a component of accumulated comprehensive income (loss). 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”). Prior period amounts continue to be reported in accordance with the Company’s historic accounting under previous lease guidance. Additionally, the Company elected a number of optional practical expedients made available under the ASC 842 transition guidance. Such elections include (i) carrying forward the Company’s historical lease classifications, (ii) foregoing a re-evaluation of historical contracts to identify embedded leases, (iii) foregoing a re-assessment of initial direct costs related to leases that existed prior to adoption, (iv) combining lease and non-lease components, 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. The Company accounts for its leases by recording right-of-use assets and lease liabilities on the Balance Sheet. 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 exclude 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 or terminate a lease when it is reasonably certain that the Company will exercise any such options. 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. Accrued Research and Development Costs Service agreements with contract research organizations (“CROs”) and contract development and manufacturing organizations (“CDMOs”) comprise a significant component of the Company’s research and development activities. External costs for CROs and CDMOs 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 CROs, CDMOs 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 CRO, CDMO 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. 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 and consists primarily of unrealized gains and losses on the Company’s investments in marketable securities. 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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Numerator: Net loss $ (39,292 ) $ (19,072 ) $ (67,116 ) $ (39,025 ) Denominator: Weighted-average shares of common stock outstanding, basic and diluted 48,816 43,115 48,753 42,868 Net loss per share, basic and diluted $ (0.80 ) $ (0.44 ) $ (1.38 ) $ (0.91 ) 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): Six Months Ended June 30, 2020 2019 Options to purchase common stock 7,016 6,976 Unvested restricted stock units 584 — Unvested restricted common stock — 19 Shares issuable under employee stock purchase plans 24 27 Total 7,624 7,022 Recently Adopted Accounting Pronouncements In June 2016 the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The FASB subsequently issued amendments to ASU 2016-13, which have the same effective date and transition date of January 1, 2020. This guidance requires companies to recognize an allowance for credit losses on available-for-sale debt securities rather than the current approach of recording a reduction to the carrying value of the asset. The Company adopted ASU 2016-13 effective January 1, 2020. The guidance limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and requires the reversal of previously recognized credit losses if fair value increases. Based on the composition of the Company’s investment portfolio and other financial assets, current economic conditions and historical credit loss activity, the adoption of the guidance did not have a material impact on the Company’s financial statements and related disclosures. During the three and six months ended June 30, 2020, the Company’s current investment portfolio was comprised of only US Treasury securities which are not in unrealized loss positions. Upon adoption, the Company did not record an allowance for credit losses on its available-for-sale debt securities. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. This ASU eliminates, modifies and adds disclosure requirements for fair value measurements. The amendments in this ASU are effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted. The Company adopted this ASU effective January 1, 2020. The Company’s adoption of this ASU did not have a material impact on its financial statements and related disclosures. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU affects general principles within Topic 740 and are meant to simplify the accounting for income taxes by removing certain exceptions to the general framework. The ASU further adds guidance to reduce complexity in certain areas, including recognizing a franchise (or similar) tax that is partially based on income as an income-based tax and incremental amounts incurred as a non-income-based tax and recognizing deferred taxes for tax goodwill. ASU 2019-12 also created an exception to the incremental approach for intraperiod tax allocation when there is a loss from continuing operations and income or a gain from other items (for example, other comprehensive income). Under the historical guidance, in this situation, an entity would have recorded an income tax provision for unrealized gains on available-for-sale securities reported in other comprehensive income, with an offsetting income tax benefit recorded in continuing operations. Per ASU 2019-12, under the new guidance, an entity would record no income tax provision in the interim period. The amendments in ASU 2019-12 are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption of the amendments is permitted, including adoption in any interim period for which financial statements have not yet been issued. An entity that elects to early adopt the amendments in an interim period should reflect any adjustments as of the beginning of the annual period that includes that interim period. Additionally, an entity that elects early adoption must adopt all the amendments in the same period. The Company elected to early adopt ASU 2019-12 effective January 1, 2020 on a prospective basis. As a result of this election, no benefit from income tax was recorded in continuing operations and no tax provision was recorded in other comprehensive income for the three and six months ended June 30, 2020 related to the Company’s loss from continuing operations and unrealized gain on available-for-sale securities during the same period. Further, the Company’s adoption had no impact to its effective tax rate. 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	6 Months Ended
	Jun. 30, 2020
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. Financial instruments that are highly liquid with original maturities of three months or less from the date of purchase are included within cash equivalents. Financial instruments that are not highly liquid, or for which their original maturities are greater than three months, are classified as investments in marketable securities. The Company’s financial assets measured at fair value on a recurring basis were as follows (in thousands): June 30, 2020 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 151,698 $ — $ — $ 151,698 Total cash equivalents 151,698 — — 151,698 Short-term marketable securities U.S. treasuries 301,048 — — 301,048 Total short-term marketable securities 301,048 — — 301,048 Total cash equivalents and short-term marketable securities $ 452,746 $ — $ — $ 452,746 December 31, 2019 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 35,935 $ — $ — $ 35,935 Total cash equivalents 35,935 — — 35,935 Short-term marketable securities U.S. treasuries 457,534 — — 457,534 Total short-term marketable securities 457,534 — — 457,534 Total cash equivalents and short-term marketable securities $ 493,469 $ — $ — $ 493,469 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 and six months ended June 30, 2020 and 2019.

Marketable Securities

Marketable Securities	6 Months Ended
	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities All marketable securities were considered available-for-sale at June 30, 2020. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type at June 30, 2020 and December 31, 2019 are summarized in the table below (in thousands): June 30, 2020 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Available-for-sale securities U.S. treasuries classified as investments $ 300,261 $ 787 $ — $ 301,048 Total available-for-sale securities $ 300,261 $ 787 $ — $ 301,048 December 31, 2019 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Available-for-sale securities U.S. treasuries classified as investments $ 457,397 $ 161 $ (24 ) $ 457,534 Total available-for-sale securities $ 457,397 $ 161 $ (24 ) $ 457,534 The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. As of June 30, 2020, the Company had no available-for-sale securities in an unrealized loss position. The aggregate fair value of securities held by the Company at December 31, 2019 in an unrealized loss position was $187.4 million, for which all of these securities had remaining maturities of less than one year as of the balance sheet date. 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 as of June 30, 2020 and December 31, 2019. There were no material realized gains or losses recognized on the sale or maturity of available-for-sale securities during the three or six months ended June 30, 2020 or 2019, 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	6 Months Ended
	Jun. 30, 2020
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): June 30, December 31, 2020 2019 Laboratory equipment $ 4,204 $ 4,170 Furniture and office equipment 1,731 1,695 Leasehold improvements 4,581 4,581 10,516 10,446 Less accumulated depreciation (2,813 ) (2,036 ) Property and equipment, net $ 7,703 $ 8,410 Depreciation and amortization expense for each of the three months ended June 30, 2020 and 2019 was $0.4 Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, December 31, 2020 2019 Accrued contract research and development expense $ 4,821 $ 4,990 Accrued compensation and benefits expense 4,478 1,608 Lease liability, current 450 410 Other current liabilities 213 90 Total $ 9,962 $ 7,098

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Lease Obligations The Company’s lease obligations primarily relate to leased office and laboratory space under noncancelable operating leases. In January 2018, the Company entered into a lease agreement for approximately 25,000 square feet of office and laboratory space in Redwood City, California (the “2018 Redwood City Lease”). The 2018 Redwood City Lease includes a contractual lease term commencing upon substantial completion and delivery of the premises, which occurred in November 2018. The Company subsequently terminated its previous lease agreement for office and laboratory space in San Carlos, California (the “2015 San Carlos Lease”). The base term of the 2018 Redwood City Lease is 10.75 years and contains a one-time option to extend the lease term for five years. This option to extend the lease term has not been included in the Company’s calculations under ASC 842 as the exercise of the option is highly uncertain and therefore deemed not probable The 2018 Redwood City Lease also included a $1.4 million tenant improvement allowance that has been applied to the total cost of tenant improvements made to the leased premises. Tenant improvement allowances received under the 2018 Redwood City Lease were recorded as leasehold improvements with an offsetting adjustment included in the Company’s calculation of its right-of-use asset under ASC 842. Leasehold improvements are depreciated over the term of the lease. In December 2019, the Company entered into an additional lease agreement for approximately 98,000 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. As described in Note 2, the Company adopted ASC 842 effective January 1, 2019. In accordance with ASC 842, the Company has performed an evaluation of its other contracts with vendors in accordance with ASC 842 and has determined that, except for the leases described above, none of its other contracts contain a lease. Classification of the Company’s lease liabilities included on the its balance sheets at June 30, 2020 was as follows (in thousands): June 30, December 31, 2020 2019 Operating lease liabilities Current portion included in accrued expenses and other current liabilities $ 450 $ 410 Non-current portion included in other long-term liabilities 7,875 8,112 Total operating lease liabilities $ 8,325 $ 8,522 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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Operating lease cost $ 279 $ 280 $ 558 $ 560 Variable cost 87 91 174 178 Total lease costs $ 366 $ 371 $ 732 $ 738 Future minimum lease payments required under operating leases include on the Company’s balance sheets at June 30, 2020 are as follows (in thousands): Fiscal Year Ending December 31, 2020 (remaining 6 months) $ 620 2021 1,270 2022 1,308 2023 1,348 2024 1,388 Thereafter 6,916 Total minimum future lease payments (1) 12,850 Less: Present value adjustment 4,525 Operating lease liabilities $ 8,325 (1) In addition to the minimum future lease commitments presented above , the lease requires the Company to pay property taxes, insurance, maintenance and repair costs. Net rent expense was $0.3 million for the each of three months ended June 30, 2020 and 2019. Net rent expense was $0.6 million for each of the six months ended June 30, 2020 and 2019. 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 June 30, 2020, the remaining lease term is 9.1 years and the discount rate used to determine the operating lease liability was 10.0%. As of June 30, 2020, 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 non-cancelable 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 June 30, 2020, the Company had $59.3 million of non-cancelable 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. 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 incurred $3.4 million of milestone expense for the three and six months ended June 30, 2020 related to development milestones associated with the first patient dosed in our Phase 3 study with lirentelimab (AK002). No milestone expense was incurred during the three and six months ended June 30, 2019. As of June 30, 2020, 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 (AK002), 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 June 30, 2020 and may be required to make aggregate additional milestone payments of up to $3.6 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 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 (AK002) 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 June 30, 2020 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 June 30, 2020. 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 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 (AK002). The proposed class period is August 5, 2019, through December 17, 2019, inclusive. 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 June 30, 2020.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2020
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 Six Months Ended June 30, June 30, 2020 0 2019 0 2020 0 2019 Research and development $ 2,585 $ 1,044 $ 5,028 $ 2,097 General and administrative 5,177 2,061 10,223 3,842 Total $ 7,762 $ 3,105 $ 15,251 $ 5,939 No income tax benefits for stock-based compensation expense have been recognized for the three and six months ended June 30, 2020 and 2019 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 June 30, 2020, the maximum number of shares that may be added to the 2018 Plan pursuant to the preceding clause is 5,098,992 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-based awards granted to employees and non-employees during the periods indicated: Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Risk-free interest rate 0.38 % 2.19 % 0.59 % 2.22 % Expected volatility 72.12 % 67.68 % 70.97 % 67.81 % Expected dividend yield — — — — Expected term (in years) 5.70 5.86 5.81 5.88 The Company’s stock option activity during the six months ended June 30, 2020 is summarized as follows (number of shares in thousands): Weighted- Average Options Exercise Outstanding Price Balance at December 31, 2019 7,148 $ 12.96 Granted 83 $ 66.48 Exercised (205 ) $ 8.47 Forfeited (10 ) $ 13.70 Balance at June 30, 2020 7,016 $ 13.73 Options exercisable 4,511 $ 7.07 Options vested and expected to vest 6,997 $ 13.68 During the three and six months ended June 30, 2020 and 2019, the Company did not grant any stock options with performance-based or market-based vesting conditions. As of June 30, 2020, total unrecognized stock-based compensation expense relating to unvested stock options was $36.6 million. This amount is expected to be recognized over a weighted-average period of 2.5 years. Restricted Stock Units RSU activity under the 2018 Plan during the six months ended June 30, 2020 is summarized as follows (in thousands, except per share data): Weighted- Average Grant Date Shares Fair Value Balance at December 31, 2019 542 $ 93.67 Granted 43 $ 66.77 Forfeited (1 ) $ 95.98 Balance at June 30, 2020 584 $ 91.65 The weighted-average fair value of RSUs granted during the six months ended June 30, 2020 was $66.77. No RSUs were granted during the six months ended June 30, 2019. As of June 30, 2020, total unrecognized stock-based compensation expense relating to unvested RSUs was $45.3 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 are 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 will 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. The Company’s first offering period under the 2018 ESPP commenced on July 18 , 2018 . During the three and six months ended June 30 , 2020 , stock-based compensation expense related to the 2018 ESPP was $ 0.2 million and $ million, respectively . During the three and six months ended June 30, 2019, stock-based compensation expense related to the 2018 ESPP was $ million and $ million, respectively.

Defined Contribution Plans

Defined Contribution Plans	6 Months Ended
	Jun. 30, 2020
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 the three and six months ended June 30, 2020, the Company made contributions to the 401(k) plan of $0.2 million and $0.3 million, respectively. During the three and six months ended June 30, 2019, the Company made contributions to the 401(k) plan of $0.1 million and $0.2 million, respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
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 June 30, 2020, the statements of operations and comprehensive loss, statements of stockholders’ equity and statements of cash flows for the three and six months ended June 30, 2020 and 2019 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 June 30, 2020 and its results of operations and comprehensive loss for the three and six months ended June 30, 2020 and 2019 and its cash flows for the six months ended June 30, 2020 and 2019. 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 December 31, 2019 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 February 25, 2020.
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 expenses related to clinical trials, calculation of right-of-use assets and lease liabilities, 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. Restricted cash as of June 30, 2020 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. 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): June 30, December 31, 2020 2019 Cash and cash equivalents $ 153,898 $ 38,367 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 156,173 $ 40,642 June 30, December 31, 2019 2018 Cash and cash equivalents $ 36,457 $ 33,660 Restricted cash in other long-term assets, deposit for lease facility 802 802 Total cash, cash equivalents and restricted cash $ 37,259 $ 34,462
Marketable Securities	Marketable Securities The Company invests in marketable securities, primarily securities issued by the U.S. 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. 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 the fair value of an available-for-sale security due to a credit loss are included in other expense, net, on the statements of operations and comprehensive loss to the extent the Company does not expect to recover the amortized cost basis. Any portion of a decline in fair value that is due to factors other than a credit loss is excluded from earnings and reported as a component of accumulated comprehensive income (loss).
Leases	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”). Prior period amounts continue to be reported in accordance with the Company’s historic accounting under previous lease guidance. Additionally, the Company elected a number of optional practical expedients made available under the ASC 842 transition guidance. Such elections include (i) carrying forward the Company’s historical lease classifications, (ii) foregoing a re-evaluation of historical contracts to identify embedded leases, (iii) foregoing a re-assessment of initial direct costs related to leases that existed prior to adoption, (iv) combining lease and non-lease components, 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. The Company accounts for its leases by recording right-of-use assets and lease liabilities on the Balance Sheet. 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 exclude 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 or terminate a lease when it is reasonably certain that the Company will exercise any such options.
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.
Accrued Research and Development Costs	Accrued Research and Development Costs Service agreements with contract research organizations (“CROs”) and contract development and manufacturing organizations (“CDMOs”) comprise a significant component of the Company’s research and development activities. External costs for CROs and CDMOs 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 CROs, CDMOs 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 CRO, CDMO 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.
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 and consists primarily of unrealized gains and losses on the Company’s investments in marketable securities.
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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Numerator: Net loss $ (39,292 ) $ (19,072 ) $ (67,116 ) $ (39,025 ) Denominator: Weighted-average shares of common stock outstanding, basic and diluted 48,816 43,115 48,753 42,868 Net loss per share, basic and diluted $ (0.80 ) $ (0.44 ) $ (1.38 ) $ (0.91 ) 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): Six Months Ended June 30, 2020 2019 Options to purchase common stock 7,016 6,976 Unvested restricted stock units 584 — Unvested restricted common stock — 19 Shares issuable under employee stock purchase plans 24 27 Total 7,624 7,022
Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2016 the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The FASB subsequently issued amendments to ASU 2016-13, which have the same effective date and transition date of January 1, 2020. This guidance requires companies to recognize an allowance for credit losses on available-for-sale debt securities rather than the current approach of recording a reduction to the carrying value of the asset. The Company adopted ASU 2016-13 effective January 1, 2020. The guidance limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and requires the reversal of previously recognized credit losses if fair value increases. Based on the composition of the Company’s investment portfolio and other financial assets, current economic conditions and historical credit loss activity, the adoption of the guidance did not have a material impact on the Company’s financial statements and related disclosures. During the three and six months ended June 30, 2020, the Company’s current investment portfolio was comprised of only US Treasury securities which are not in unrealized loss positions. Upon adoption, the Company did not record an allowance for credit losses on its available-for-sale debt securities. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. This ASU eliminates, modifies and adds disclosure requirements for fair value measurements. The amendments in this ASU are effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted. The Company adopted this ASU effective January 1, 2020. The Company’s adoption of this ASU did not have a material impact on its financial statements and related disclosures. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU affects general principles within Topic 740 and are meant to simplify the accounting for income taxes by removing certain exceptions to the general framework. The ASU further adds guidance to reduce complexity in certain areas, including recognizing a franchise (or similar) tax that is partially based on income as an income-based tax and incremental amounts incurred as a non-income-based tax and recognizing deferred taxes for tax goodwill. ASU 2019-12 also created an exception to the incremental approach for intraperiod tax allocation when there is a loss from continuing operations and income or a gain from other items (for example, other comprehensive income). Under the historical guidance, in this situation, an entity would have recorded an income tax provision for unrealized gains on available-for-sale securities reported in other comprehensive income, with an offsetting income tax benefit recorded in continuing operations. Per ASU 2019-12, under the new guidance, an entity would record no income tax provision in the interim period. The amendments in ASU 2019-12 are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption of the amendments is permitted, including adoption in any interim period for which financial statements have not yet been issued. An entity that elects to early adopt the amendments in an interim period should reflect any adjustments as of the beginning of the annual period that includes that interim period. Additionally, an entity that elects early adoption must adopt all the amendments in the same period. The Company elected to early adopt ASU 2019-12 effective January 1, 2020 on a prospective basis. As a result of this election, no benefit from income tax was recorded in continuing operations and no tax provision was recorded in other comprehensive income for the three and six months ended June 30, 2020 related to the Company’s loss from continuing operations and unrealized gain on available-for-sale securities during the same period. Further, the Company’s adoption had no impact to its effective tax rate. Impact of Recent Legislation

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2020
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): June 30, December 31, 2020 2019 Cash and cash equivalents $ 153,898 $ 38,367 Restricted cash in other long-term assets, deposit for lease facility 2,275 2,275 Total cash, cash equivalents and restricted cash $ 156,173 $ 40,642 June 30, December 31, 2019 2018 Cash and cash equivalents $ 36,457 $ 33,660 Restricted cash in other long-term assets, deposit for lease facility 802 802 Total cash, cash equivalents and restricted cash $ 37,259 $ 34,462
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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Numerator: Net loss $ (39,292 ) $ (19,072 ) $ (67,116 ) $ (39,025 ) Denominator: Weighted-average shares of common stock outstanding, basic and diluted 48,816 43,115 48,753 42,868 Net loss per share, basic and diluted $ (0.80 ) $ (0.44 ) $ (1.38 ) $ (0.91 )
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): Six Months Ended June 30, 2020 2019 Options to purchase common stock 7,016 6,976 Unvested restricted stock units 584 — Unvested restricted common stock — 19 Shares issuable under employee stock purchase plans 24 27 Total 7,624 7,022

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2020
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): June 30, 2020 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 151,698 $ — $ — $ 151,698 Total cash equivalents 151,698 — — 151,698 Short-term marketable securities U.S. treasuries 301,048 — — 301,048 Total short-term marketable securities 301,048 — — 301,048 Total cash equivalents and short-term marketable securities $ 452,746 $ — $ — $ 452,746 December 31, 2019 Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 35,935 $ — $ — $ 35,935 Total cash equivalents 35,935 — — 35,935 Short-term marketable securities U.S. treasuries 457,534 — — 457,534 Total short-term marketable securities 457,534 — — 457,534 Total cash equivalents and short-term marketable securities $ 493,469 $ — $ — $ 493,469

Marketable Securities (Tables)

Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Marketable Securities	All marketable securities were considered available-for-sale at June 30, 2020. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type at June 30, 2020 and December 31, 2019 are summarized in the table below (in thousands): June 30, 2020 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Available-for-sale securities U.S. treasuries classified as investments $ 300,261 $ 787 $ — $ 301,048 Total available-for-sale securities $ 300,261 $ 787 $ — $ 301,048 December 31, 2019 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Available-for-sale securities U.S. treasuries classified as investments $ 457,397 $ 161 $ (24 ) $ 457,534 Total available-for-sale securities $ 457,397 $ 161 $ (24 ) $ 457,534

Balance Sheet Components and _2

Balance Sheet Components and Supplemental Disclosures (Tables)	6 Months Ended
	Jun. 30, 2020
Balance Sheet Related Disclosures [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net, consisted of the following (in thousands): June 30, December 31, 2020 2019 Laboratory equipment $ 4,204 $ 4,170 Furniture and office equipment 1,731 1,695 Leasehold improvements 4,581 4,581 10,516 10,446 Less accumulated depreciation (2,813 ) (2,036 ) Property and equipment, net $ 7,703 $ 8,410
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, December 31, 2020 2019 Accrued contract research and development expense $ 4,821 $ 4,990 Accrued compensation and benefits expense 4,478 1,608 Lease liability, current 450 410 Other current liabilities 213 90 Total $ 9,962 $ 7,098

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Summary of Classification of Company's Lease Liabilities	Classification of the Company’s lease liabilities included on the its balance sheets at June 30, 2020 was as follows (in thousands): June 30, December 31, 2020 2019 Operating lease liabilities Current portion included in accrued expenses and other current liabilities $ 450 $ 410 Non-current portion included in other long-term liabilities 7,875 8,112 Total operating lease liabilities $ 8,325 $ 8,522
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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Operating lease cost $ 279 $ 280 $ 558 $ 560 Variable cost 87 91 174 178 Total lease costs $ 366 $ 371 $ 732 $ 738
Summary of Future Minimum Lease Payments Required Under Operating Leases	Future minimum lease payments required under operating leases include on the Company’s balance sheets at June 30, 2020 are as follows (in thousands): Fiscal Year Ending December 31, 2020 (remaining 6 months) $ 620 2021 1,270 2022 1,308 2023 1,348 2024 1,388 Thereafter 6,916 Total minimum future lease payments (1) 12,850 Less: Present value adjustment 4,525 Operating lease liabilities $ 8,325 (1)

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2020
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 Six Months Ended June 30, June 30, 2020 0 2019 0 2020 0 2019 Research and development $ 2,585 $ 1,044 $ 5,028 $ 2,097 General and administrative 5,177 2,061 10,223 3,842 Total $ 7,762 $ 3,105 $ 15,251 $ 5,939
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-based awards granted to employees and non-employees during the periods indicated: Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Risk-free interest rate 0.38 % 2.19 % 0.59 % 2.22 % Expected volatility 72.12 % 67.68 % 70.97 % 67.81 % Expected dividend yield — — — — Expected term (in years) 5.70 5.86 5.81 5.88
Summary of Stock Option Activity	The Company’s stock option activity during the six months ended June 30, 2020 is summarized as follows (number of shares in thousands): Weighted- Average Options Exercise Outstanding Price Balance at December 31, 2019 7,148 $ 12.96 Granted 83 $ 66.48 Exercised (205 ) $ 8.47 Forfeited (10 ) $ 13.70 Balance at June 30, 2020 7,016 $ 13.73 Options exercisable 4,511 $ 7.07 Options vested and expected to vest 6,997 $ 13.68
Summary of Restricted Stock Awards and Restricted Stock Units	RSU activity under the 2018 Plan during the six months ended June 30, 2020 is summarized as follows (in thousands, except per share data): Weighted- Average Grant Date Shares Fair Value Balance at December 31, 2019 542 $ 93.67 Granted 43 $ 66.77 Forfeited (1 ) $ 95.98 Balance at June 30, 2020 584 $ 91.65

Organization and Business - Add

Organization and Business - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Net loss	$ 39,292	$ 27,824	$ 19,072	$ 19,953	$ 67,116	$ 39,025
Cash used in operations					43,686	$ 27,702
Accumulated deficit	256,600				256,600		$ 189,484
Cash, cash equivalents and marketable securities	$ 454,900				$ 454,900

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Restricted cash in other long term assets, deposit for lease facility	$ 2,275,000	$ 2,275,000		$ 2,275,000	$ 802,000	$ 802,000
ASU 2016-13
Summary Of Significant Accounting Policies [Line Items]
Debt Securities, available-for-sale, allowance for credit loss			$ 0
ASU 2019-12
Summary Of Significant Accounting Policies [Line Items]
Income tax benefit, continuing operations	0	0
Income tax provision, other comprehensive Income	$ 0	$ 0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 153,898	$ 38,367	$ 36,457	$ 33,660
Restricted cash in other long-term assets, deposit for lease facility	2,275	2,275	802	802
Total cash, cash equivalents and restricted cash	$ 156,173	$ 40,642	$ 37,259	$ 34,462

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				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss	$ (39,292)	$ (27,824)	$ (19,072)	$ (19,953)	$ (67,116)	$ (39,025)
Weighted-average number of common shares outstanding:
Weighted-average shares of common stock outstanding, basic and diluted	48,816		43,115		48,753	42,868
Net loss per share, basic and diluted	$ (0.80)		$ (0.44)		$ (1.38)	$ (0.91)

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	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
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	7,624	7,022
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	7,016	6,976
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	584	0
Unvested Restricted 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	0	19
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	24	27

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	$ 301,048	$ 457,534
Fair Value, Measurements, Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	151,698	35,935
Short-term marketable securities	301,048	457,534
Total cash equivalents and short-term marketable securities	452,746	493,469
Fair Value, Measurements, Recurring Basis | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	151,698	35,935
Short-term marketable securities	301,048	457,534
Total cash equivalents and short-term marketable securities	452,746	493,469
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	151,698	35,935
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	151,698	35,935
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	301,048	457,534
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	301,048	457,534
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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Transfers of assets between level 1 to level 2	$ 0	$ 0	$ 0	$ 0
Transfers of assets between level 2 to level 1	0	0	0	0
Transfers of liabilities between level 1 to level 2	0	0	0	0
Transfers of liabilities between level 2 to level 1	0	0	0	0
Transfers of assets into level 3	0	0	0	0
Transfers of assets out of level 3	0	0	0	0
Transfers of liabilities into level 3	0	0	0	0
Transfers of liabilities out of level 3	$ 0	$ 0	$ 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 ($)	Jun. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 300,261,000	$ 457,397,000
Unrealized Gains	787,000	161,000
Unrealized Losses	0	(24,000)
Fair Value	301,048,000	457,534,000
U.S. Treasuries | Investments
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	300,261,000	457,397,000
Unrealized Gains	787,000	161,000
Unrealized Losses	0	(24,000)
Fair Value	$ 301,048,000	$ 457,534,000

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, unrealized losses	$ 0		$ 0		$ 24,000
Available-for-sale securities, continuous unrealized loss position, fair value					$ 187,400,000
Available-for-sale Securities, realized gains	0	$ 0	0	$ 0
Available-for-sale Securities, realized losses	$ 0	$ 0	$ 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	Jun. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 10,516	$ 10,446
Less accumulated depreciation	(2,813)	(2,036)
Property and equipment, net	7,703	8,410
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,204	4,170
Furniture And Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,731	1,695
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4,581	$ 4,581

Balance Sheet Components and _4

Balance Sheet Components and Supplemental Disclosures - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization	$ 400	$ 400	$ 777	$ 732

Balance Sheet Components and _5

Balance Sheet Components and Supplemental Disclosures - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued contract research and development expense	$ 4,821	$ 4,990
Accrued compensation and benefits expense	4,478	1,608
Lease liability, current	450	410
Other current liabilities	213	90
Total	$ 9,962	$ 7,098

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended		3 Months Ended		6 Months Ended		79 Months Ended	81 Months Ended
	Dec. 31, 2019USD ($)ft²shares	Jan. 31, 2018USD ($)ft²	Jun. 30, 2020USD ($)shares	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)shares	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)shares	Jun. 30, 2020USD ($)shares	Dec. 31, 2013shares
Commitments And Contingencies [Line Items]
Operating lease right-of-use assets	$ 5,775,000		$ 5,633,000		$ 5,633,000		$ 5,633,000	$ 5,633,000
Operating lease liabilities	$ 8,522,000		8,325,000		8,325,000		$ 8,325,000	$ 8,325,000
Net rent expense			$ 300,000	$ 300,000	$ 600,000	$ 600,000
Remaining lease term			9 years 1 month 6 days		9 years 1 month 6 days		9 years 1 month 6 days	9 years 1 month 6 days
Operating lease liability discount rate			10.00%		10.00%		10.00%	10.00%
Non-cancelable purchase obligations			$ 59,300,000		$ 59,300,000		$ 59,300,000	$ 59,300,000
Common stock, shares issued | shares	48,668,000		48,913,000		48,913,000		48,913,000	48,913,000
In-Licensing Agreements
Commitments And Contingencies [Line Items]
Milestone expense			$ 3,400,000	$ 0	$ 3,400,000	$ 0
Accrued Royalties			0		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							3,600,000
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 | Minimum
Commitments And Contingencies [Line Items]
Annual commercial license fees								40,000
Non-exclusive License Agreement with BioWa Inc. and Lonza Sales AG | Maximum
Commitments And Contingencies [Line Items]
Aggregate additional milestone payments								38,000,000
2019 San Carlos Lease Agreement
Commitments And Contingencies [Line Items]
Lease agreement initiation period	2019-12
Lease term extension period	5 years
Area of office and laboratory space | ft²	98,000
Lessee operating lease contractual lease expected commencement period	2020-11
Lessee operating lease expected termination Period	2031-08
Operating lease, future minimum rental payments	$ 77,600,000
Operating lease right-of-use assets			0		0		0	0
Operating lease liabilities			0		0		0	0
Security deposit in the form of letter of credit secured by restricted cash			1,500,000		1,500,000		1,500,000	1,500,000
2018 Redwood City Lease Agreement
Commitments And Contingencies [Line Items]
Lease agreement initiation period		2018-01
Base term of lease		10 years 9 months
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	$ 800,000

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Classification of Company's Lease Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Operating lease liabilities
Current portion included in accrued expenses and other current liabilities	$ 450	$ 410
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent
Non-current portion included in other long-term liabilities	$ 7,875	$ 8,112
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Total operating lease liabilities	$ 8,325	$ 8,522

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Components of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Operating lease cost	$ 279	$ 280	$ 558	$ 560
Variable cost	87	91	174	178
Total lease costs	$ 366	$ 371	$ 732	$ 738

Commitments and Contingencies_4

Commitments and Contingencies - Summary of Future Minimum Lease Payments Required Under Operating Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Operating Lease Liabilities Payments Due [Abstract]
2020 (remaining 6 months)	$ 620
2021	1,270
2022	1,308
2023	1,348
2024	1,388
Thereafter	6,916
Total minimum future lease payments	12,850
Present value adjustment	4,525
Operating lease liabilities	$ 8,325	$ 8,522

Commitments and Contingencies_5

Commitments and Contingencies - Summary of Future Minimum Lease Payments Required Under Operating Leases (Parenthetical) (Details) $ in Thousands	Jun. 30, 2020USD ($)
Commitments And Contingencies [Line Items]
Minimum future lease payments	$ 12,850
2019 San Carlos Lease Agreement
Commitments And Contingencies [Line Items]
Minimum future lease payments	$ 77,600

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Total Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 7,762	$ 3,105	$ 15,251	$ 5,939
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2,585	1,044	5,028	2,097
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 5,177	$ 2,061	$ 10,223	$ 3,842

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Tax benefits for stock-based compensation expense recognized		$ 0	$ 0	$ 0	$ 0
Stock options granted				83,000
Total unrecognized stock-based compensation expense relating to unvested stock options		36,600,000		$ 36,600,000
Total stock-based compensation expense		$ 7,762,000	$ 3,105,000	$ 15,251,000	$ 5,939,000
Performance-Based Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted		0	0	0	0
Market-Based Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted		0	0	0	0
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average recognition period				2 years 6 months
Unvested 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				$ 66.77
Number of RSUs granted				43,000	0
Total unrecognized stock-based compensation expense		$ 45,300,000		$ 45,300,000
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	$ 400,000	$ 300,000
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%
Maximum number of additional shares authorized to be added to the Plan				5,098,992
2012 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period	4 years
2012 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-based Awards Granted (Details) - Employees and Non-Employees - Stock Options	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.38%	2.19%	0.59%	2.22%
Expected volatility	72.12%	67.68%	70.97%	67.81%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)	5 years 8 months 12 days	5 years 10 months 9 days	5 years 9 months 21 days	5 years 10 months 17 days

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock Option Activity (Details) - $ / shares shares in Thousands	6 Months Ended
	Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Beginning balance	7,148
Options Outstanding, Granted	83
Options Outstanding, Exercised	(205)
Options Outstanding, forfeited	(10)
Options Outstanding, Ending balance	7,016
Options Outstanding, Options exercisable	4,511
Options Outstanding, Options vested and expected to vest	6,997
Weighted Average Exercise Price, Beginning balance	$ 12.96
Weighted Average Exercise Price, Granted	66.48
Weighted Average Exercise Price, Exercised	8.47
Weighted Average Exercise Price, Forfeited	13.70
Weighted Average Exercise Price, Ending balance	13.73
Weighted Average Exercise Price, Options exercisable	7.07
Weighted Average Exercise Price, Options vested and expected to vest	$ 13.68

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of RSU Activity Under 2018 Plan (Details) - Unvested Restricted Stock Units - $ / shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Number of Shares
Balance at December 31, 2019	542,000
Granted	43,000	0
Forfeited	(1,000)
Balance at June 30, 2020	584,000
Weighted-Average Grant Date Fair Value
Balance at December 31, 2019	$ 93.67
Granted	66.77
Forfeited	95.98
Balance at June 30, 2020	$ 91.65

Defined Contribution Plans - Ad

Defined Contribution Plans - Additional Information (Details) - 401(K) Plan - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Contribution Plan Disclosure [Line Items]
Employer contribution matching percentage			4.00%
Contributions made by employer	$ 0.2	$ 0.1	$ 0.3	$ 0.2