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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	Apr. 29, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-38311
Entity Registrant Name	Denali Therapeutics Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-3872213
Entity Address, Address Line One	161 Oyster Point Blvd
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	866-8548
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	DNLI
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (shares)		105,628,182
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Central Index Key	0001714899
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 207,537	$ 79,449
Short-term marketable securities	379,713	335,907
Prepaid expenses and other current assets	17,535	14,675
Total current assets	604,785	430,031
Long-term marketable securities	9,684	39,886
Property and equipment, net	45,452	46,732
Operating lease right-of-use asset	33,626	33,923
Other non-current assets	2,318	2,659
Total assets	695,865	553,231
Current liabilities:
Accounts payable	2,316	2,590
Accrued compensation	3,910	8,739
Accrued clinical costs	5,349	5,042
Other accruals and other current liabilities	7,265	6,569
Operating lease liability, current	4,121	3,665
Contract liabilities	24,674	18,739
Total current liabilities	47,635	45,344
Contract liabilities, less current portion	34,747	43,753
Operating lease liability, less current portion	67,793	68,865
Other non-current liabilities	379	379
Total liabilities	150,554	158,341
Commitments and contingencies (Note 8)
Stockholders' equity:
Convertible preferred stock, $0.01 par value; 40,000,000 shares authorized as of March 31, 2020 and December 31, 2019; 0 shares issued and outstanding as of March 31, 2020 and December 31, 2019	0	0
Common stock, $0.01 par value; 400,000,000 shares authorized as of March 31, 2020 and December 31, 2019; 105,541,343 shares and 96,189,935 shares issued and outstanding as of March 31, 2020 and December 31, 2019, respectively	1,382	1,288
Additional paid-in capital	1,025,408	818,803
Accumulated other comprehensive income	835	350
Accumulated deficit	(482,314)	(425,551)
Total stockholders' equity	545,311	394,890
Total liabilities and stockholders’ equity	$ 695,865	$ 553,231

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Convertible preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Convertible preferred stock, shares authorized (in shares)	40,000,000	40,000,000
Convertible preferred stock, shares issued (in shares)	0	0
Convertible preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares issued (in shares)	105,541,343	96,189,935
Common stock, shares outstanding (in shares)	105,541,343	96,189,935

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Collaboration revenue:
Collaboration revenue from customers	$ 3,552	$ 4,111
Other collaboration revenue	52	94
Total collaboration revenue	3,604	4,205
Operating expenses:
Research and development	51,016	37,403
General and administrative	12,555	9,310
Total operating expenses	63,571	46,713
Loss from operations	(59,967)	(42,508)
Interest and other income, net	3,069	3,516
Loss before income taxes	(56,898)	(38,992)
Income tax benefit	135	0
Net loss	(56,763)	(38,992)
Other comprehensive income (loss):
Net unrealized gain on marketable securities, net of tax	485	981
Comprehensive loss	$ (56,278)	$ (38,011)
Net loss per share, basic and diluted (usd per share)	$ (0.55)	$ (0.41)
Weighted average number of shares outstanding, basic and diluted (in shares)	102,419,718	94,984,503

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Common stock, shares outstanding beginning balance (in shares) at Dec. 31, 2018		94,662,435
Beginning balance at Dec. 31, 2018	$ 546,845	$ 1,273	$ 774,158	$ (649)	$ (227,937)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances under equity incentive plans (in shares)		199,503
Issuances under equity incentive plans	908	$ 2	906
Vesting of early exercised common stock (in shares)		46,874
Vesting of early exercised common stock	32	$ 1	31
Vesting of restricted stock awards and units (in shares)		348,893
Vesting of restricted stock awards	0	$ 3	(3)
Stock-based compensation	6,874		6,874
Net loss	(38,992)				(38,992)
Other comprehensive lncome	981			981
Common stock, shares outstanding ending balance (in shares) at Mar. 31, 2019		95,257,705
Ending balance at Mar. 31, 2019	$ 516,648	$ 1,279	781,966	332	(266,929)
Common stock, shares outstanding beginning balance (in shares) at Dec. 31, 2019	96,189,935	96,189,935
Beginning balance at Dec. 31, 2019	$ 394,890	$ 1,288	818,803	350	(425,551)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in follow-on offering, net of issuance costs of $632 (in shares)		9,000,000
Issuance of common stock in follow-on offering, net of issuance costs of $632	193,948	$ 90	193,858
Issuances under equity incentive plans (in shares)		259,569
Issuances under equity incentive plans	1,966	$ 3	1,963
Vesting of restricted stock awards and units (in shares)		91,839
Vesting of restricted stock awards	0	$ 1	(1)
Stock-based compensation	10,785		10,785
Net loss	(56,763)				(56,763)
Other comprehensive lncome	$ 485			485
Common stock, shares outstanding ending balance (in shares) at Mar. 31, 2020	105,541,343	105,541,343
Ending balance at Mar. 31, 2020	$ 545,311	$ 1,382	$ 1,025,408	$ 835	$ (482,314)

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Common Stock
Common stock issuance costs	$ 632

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (56,763)	$ (38,992)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,109	2,403
Stock–based compensation expense	10,785	6,874
Net amortization of discounts on marketable securities	(607)	(1,317)
Non-cash operating lease expense	321	1,265
Other non-cash items	(53)	0
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,454)	2,849
Accounts payable	(292)	1,965
Accruals and other current liabilities	(3,827)	(4,593)
Contract liabilities	(3,069)	(777)
Operating lease liability	(642)	0
Net cash used in operating activities	(54,492)	(30,323)
Investing activities
Purchases of marketable securities	(153,155)	(109,810)
Purchases of property and equipment	(879)	(2,028)
Maturities and sales of marketable securities	140,701	103,791
Net cash used in investing activities	(13,333)	(8,047)
Financing activities
Proceeds from public offering of common stock, net of issuance costs	193,948	0
Proceeds from exercise of awards under equity incentive plans	1,965	908
Net cash provided by financing activities	195,913	908
Net increase (decrease) in cash, cash equivalents and restricted cash	128,088	(37,462)
Cash, cash equivalents and restricted cash at beginning of period	80,949	78,623
Cash, cash equivalents and restricted cash at end of period	209,037	41,161
Supplemental disclosures of cash flow information
Tenant improvements provided by the landlord	0	11,341
Property and equipment purchases accrued but not yet paid	$ 0	$ 1,569

Significant Accounting Policies	3 Months Ended
Significant Accounting Policies	Mar. 31, 2020
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Organization and Description of Business Denali Therapeutics Inc. ("Denali" or the “Company”) is a biopharmaceutical company, incorporated in Delaware, that discovers and develops therapeutics to defeat neurodegenerative diseases. The Company is headquartered in South San Francisco, California. Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial information and the instructions to Form 10-Q and Article 10 of SEC Regulation S-X for interim financial information. These unaudited condensed consolidated financial statements and notes should be read in conjunction with the audited consolidated financial statements and notes thereto contained in the Annual Report on Form 10-K for the year ended December 31, 2019, as filed with the Securities and Exchange Commission on February 27, 2020 (the "2019 Annual Report on Form 10-K"). The Condensed Consolidated Balance Sheet as of December 31, 2019 was derived from the audited annual consolidated financial statements as of the period then ended. Certain information and footnote disclosures typically included in the Company's annual consolidated financial statements have been condensed or omitted. The accompanying unaudited condensed consolidated financial statements reflect all adjustments that, in the opinion of management, are necessary for a fair statement of the results of the interim periods presented. All such adjustments are of a normal recurring nature except for the impacts of adopting new accounting standards discussed below. These interim financial results are not necessarily indicative of results expected for the full fiscal year or for any subsequent interim period. During the three months ended March 31, 2020, except as discussed below in the sections titled "Marketable Securities" and "Recently Adopted Accounting Pronouncement," there were no material changes to the Company's significant accounting and financial reporting policies from those reflected in the 2019 Annual Report on Form 10-K. For further information with regard to the Company’s Significant Accounting Policies, please refer to Note 1, "Significant Accounting Policies," to the Company’s Consolidated Financial Statements included in the 2019 Annual Report on Form 10-K. Principles of Consolidation These unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation. For the Company and its subsidiary, the functional currency has been determined to be U.S. dollars. Monetary assets and liabilities denominated in foreign currency are remeasured at period-end exchange rates. Non-monetary assets and liabilities denominated in foreign currencies are remeasured at historical rates. Foreign currency transaction gains and losses resulting from remeasurement are recognized in interest and other income, net in the Condensed Consolidated Statements of Operations and Comprehensive Loss. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires the Company to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities at the date of the condensed consolidated financial statements, as well as the reported amounts of expenses during the reporting period. Actual results could differ from those estimates, and such differences could be material to the Condensed Consolidated Balance Sheets and Statements of Operations and Comprehensive Loss. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities and forward foreign currency exchange contracts. Substantially all of the Company’s cash and cash equivalents are deposited in accounts with financial institutions that management believes are of high credit quality. Such deposits have and will continue to exceed federally insured limits. The Company maintains its cash with accredited financial institutions and accordingly, such funds are subject to minimal credit risk. The Company’s investment policy limits investments to certain types of securities issued by the U.S. government, its agencies and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash, cash equivalents and marketable securities and issuers of marketable securities to the extent recorded on the Condensed Consolidated Balance Sheets. As of March 31, 2020 and December 31, 2019, the Company had no off-balance sheet concentrations of credit risk. The Company is exposed to counterparty credit risk on all of its derivative financial instruments. The Company has established and maintains strict counterparty credit guidelines and enters into hedges only with financial institutions that are investment grade or better to minimize the Company’s exposure to potential defaults. The Company does not require collateral to be pledged under these agreements. The Company is subject to a number of risks similar to other early-stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of current or future preclinical testing or clinical trials, its reliance on third parties to conduct its clinical trials, the need to obtain regulatory and marketing approvals for its product candidates, competitors developing new technological innovations, 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 any license or collaboration agreements, and the need to secure and maintain adequate manufacturing arrangements with third parties. If the Company does not successfully commercialize or partner any of its product candidates, it will be unable to generate product revenue or achieve profitability. The COVID-19 pandemic has caused increased risk and uncertainty for the Company. Credit risk associated with investments in securities may increase if any institution with which the Company has an investment is significantly impacted by the COVID-19 pandemic. As of March 31, 2020, the Company has not realized any losses on its cash deposits or investments. Further, COVID-19 may impact the timelines and progress of the Company's preclinical activities and clinical trials, and may impact its ability to raise capital in the near term. Segments The Company has one operating segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with original maturities of 90 days or less at the date of purchase to be cash and cash equivalents. Cash equivalents are reported at fair value. The Company’s restricted cash consists of the letter of credit for the Company’s headquarters building lease, and is included within other non-current assets on the accompanying Condensed Consolidated Balance Sheets. Marketable Securities The Company generally invests its excess cash in money market funds and investment grade short to intermediate-term fixed income securities. Such investments are included in cash and cash equivalents, short-term marketable securities, or long-term marketable securities on the Condensed Consolidated Balance Sheets, are considered available-for-sale, and reported at fair value with net unrealized gains and losses included as a component of stockholders’ equity. The Company classifies investments in securities with remaining maturities of less than one year, or where its intent is to use the investments to fund current operations or to make them available for current operations, as short-term investments. The Company classifies investments in securities with remaining maturities of over one year as long-term investments. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in interest and other income, net in the Condensed Consolidated Statements of Operations and Comprehensive Loss. Realized gains and losses and declines in value determined to be due to credit losses on marketable securities, if any, are included in interest and other income, net. The Company periodically evaluates the need for an allowance for credit losses. This evaluation consists of several qualitative and quantitative factors, including whether it has plans to sell the security, whether it is more likely than not it will be required to sell any marketable securities before recovery of its amortized cost basis, and if the entity has the ability and intent to hold the security to maturity, and the portion of any unrealized loss that is the result of a credit loss. Factors considered in making these evaluations include quoted market prices, recent financial results and operating trends, implied values from any recent transactions or offers of investee securities, credit quality of debt instrument issuers, expected cash flows from securities, other publicly available information that may affect the value of the marketable security, duration and severity of the decline in value, and the Company's strategy and intentions for holding the marketable security. Accounts Receivable Accounts receivable are included within prepaid expenses and other current assets on the Condensed Consolidated Balance Sheets. The accounts receivable balance represents amounts receivable from the Company's collaboration partners, net of an allowance for credit losses, if required. Derivatives and Hedging Activities The Company measures its derivative instruments at fair value, and accounts them as either assets or liabilities included within prepaid assets and other current assets and other accruals and current liabilities, respectively, on the Condensed Consolidated Balance Sheets. Derivatives are adjusted to fair value through interest and other income, net in the Condensed Consolidated Statements of Operations and Comprehensive Loss. Leases The Company adopted Accounting Standards Update ("ASU") No. 2016-02, Leases as of January 1, 2019. A determination is made as to whether an arrangement is a lease at inception. A right-of-use (“ROU”) asset and operating lease liability is recognized for identified operating leases in the Condensed Consolidated Balance Sheets. ROU assets represent the Company’s right to use the underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments due over the lease term, with the ROU assets adjusted for lease incentives received. When determining the present value of lease payments, the Company uses its incremental borrowing rate on the date of lease commencement, or the rate implicit in the lease, if known. The Company does not assume renewals in its determination of the lease term unless the renewals are deemed by management to be reasonably certain at lease inception. Leases with an initial term of 12 months or less are not recorded on the balance sheet, unless they include an option to purchase the underlying asset that the Company is reasonably certain to exercise. The Company recognizes lease expenses on a straight-line basis over the lease term. The Company has leases with lease and non-lease components, which the Company has elected to account for as a single lease component. Revenue Recognition License and Collaboration Revenue The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (“ASC 808”) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and, therefore, within the scope of Topic 606. For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to Topic 606. The accounting treatment pursuant to Topic 606 is outlined below. The terms of licensing and collaboration agreements entered into typically include payment of one or more of the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply and research and development services; and royalties on net sales of licensed products. Each of these payments results in license, collaboration and other revenue, except for revenues from royalties on net sales of licensed products, which are classified as royalty revenue. The core principle of Topic 606 is to recognize revenue when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Amounts received prior to satisfying the revenue recognition criteria are recorded as contract liabilities in the Company’s Condensed Consolidated Balance Sheets. If the related performance obligation is expected to be satisfied within the next twelve months this will be classified in current liabilities. Amounts recognized as revenue prior to the Company having an unconditional right (other than a right that is conditioned only on the passage of time) to receipt are recorded as contract assets in the Company's Condensed Consolidated Balance Sheets. If the Company expects to have an unconditional right to receive the consideration in the next twelve months, this will be classified in current assets. A net contract asset or liability is presented for each contract with a customer. At contract inception, the Company assesses the goods or services promised in a contract with a customer and identifies those distinct goods and services that represent a performance obligation. A promised good or service may not be identified as a performance obligation if it is immaterial in the context of the contract with the customer, if it is not separately identifiable from other promises in the contract (either because it is not capable of being separated or because it is not separable in the context of the contract), or if the performance obligation does not provide the customer with a material right. The Company considers the terms of the contract to determine the transaction price. The transaction price is the amount of consideration to which the Company expects to be entitled in exchange for transferring promised goods or services to a customer. The consideration promised in a contract with a customer may include fixed amounts, variable amounts, or both. Variable consideration will only be included in the transaction price when it is not considered constrained, which is when it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur. If it is determined that multiple performance obligations exist, the transaction price is allocated at the inception of the agreement to all identified performance obligations based on the relative standalone selling prices ("SSP"). The relative SSP for each deliverable is estimated using external sourced evidence if it is available. If external sourced evidence is not available, the Company uses its best estimate of the SSP for the deliverable. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset, which for a service is considered to be as the services are received and used. The Company recognizes revenue over time by measuring the progress toward complete satisfaction of the relevant performance obligation using an appropriate input or output method based on the nature of the service promised to the customer. After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the transaction price is allocated to the performance obligations on the same basis as at contract inception. Management may be required to exercise considerable judgment in estimating revenue to be recognized. Judgment is required in identifying performance obligations, estimating the transaction price, estimating the SSP of identified performance obligations, which may include forecasted revenue, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success, and estimating the progress towards satisfaction of performance obligations. Comprehensive Income (Loss) Comprehensive income (loss) is composed of net loss and certain changes in stockholders’ equity (deficit) that are excluded from net loss, primarily unrealized gains or losses on the Company’s marketable securities. Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented. Recently Issued Accounting Pronouncement In December 2019, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. 2019-12, Income Taxes (Topic 740) Simplifying the Accounting for Income Taxes. ASU No. 2019-12 modifies ASC 740 to simplify several aspects of accounting for income taxes, including eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation. The guidance is effective for fiscal years beginning after December 15, 2020 and interim periods within those fiscal years, with early adoption permitted, and is required to be adopted prospectively, with the exception of certain specific amendments. The Company is currently assessing the impact of this ASU on its Condensed Consolidated Financial Statements. Recently Adopted Accounting Pronouncement In June 2016, the FASB issued Accounting Standards Update No. 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments. ASU 2016-13 requires measurement and recognition of expected credit losses for financial assets. In April 2019, the FASB issued clarification to ASU 2016-13 within ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments-Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments. The Company adopted this standard as of January 1, 2020 using a modified retrospective approach. Adoption of the standard did not have a material impact on the Condensed Consolidated Financial Statements.

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

Assets and liabilities measured at fair value at each balance sheet date are as follows (in thousands):


	March 31, 2020
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	92,160	$	—	$	—	$	92,160
U.S. government treasuries	84,996		—		—		84,996
Commercial paper	—		2,996		—		2,996
Short-term marketable securities:
U.S. government treasuries	273,680		—		—		273,680

Corporate debt securities	—		61,766		—		61,766
Commercial paper	—		44,267		—		44,267
Long-term marketable securities:
U.S. government treasuries	2,565		—		—		2,565

Corporate debt securities	—		7,119		—		7,119

Total	$	453,401	$	116,148	$	—	$	569,549
Liabilities:
Foreign currency derivative contracts	$	—	$	141	$	—	$	141
Total	$	—	$	141	$	—	$	141


	December 31, 2019
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	54,163	$	—	$	—	$	54,163
U.S. government treasuries	15,989		—		—		15,989
Short-term marketable securities:
U.S. government treasuries	250,070		—		—		250,070
U.S. government agency securities	—		2,000		—		2,000
Corporate debt securities	—		53,479		—		53,479
Commercial paper	—		30,358		—		30,358
Long-term marketable securities:
U.S. government treasuries	13,869		—		—		13,869
Corporate debt securities	—		26,017		—		26,017
Foreign currency derivative contracts	—		85		—		85
Total	$	334,091	$	111,939	$	—	$	446,030
Liabilities:
Foreign currency derivative contracts	$	—	$	8	$	—	$	8
Total	$	—	$	8	$	—	$	8

The carrying amounts of prepaid expenses and other current assets, accounts payable and accrued liabilities approximate their fair values due to their short-term maturities.

The Company’s Level 2 securities are valued using third-party pricing sources. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly.

There were no transfers of assets or liabilities between the fair value measurement levels during the three months ended March 31, 2020 or 2019.

- Definition

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

+ References + Details

Cash and Marketable Securities

3 Months Ended

Mar. 31, 2020

Cash and Cash Equivalents [Abstract]

Cash and Marketable Securities

Cash, cash equivalents and restricted cash

A reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Consolidated Balance Sheets to the amount reported within the Condensed Consolidated Statements of Cash Flows is shown in the table below (in thousands):


	March 31,			December 31,			March 31,			December 31,
			2020			2019			2019			2018
Cash and cash equivalents	$	207,537		$	79,449		$	39,661		$	77,123
Restricted cash included within other non-current assets	1,500			1,500			1,500			1,500
Total cash, cash equivalents, and restricted cash	$	209,037		$	80,949		$	41,161		$	78,623

Marketable securities

All marketable securities were considered available-for-sale at March 31, 2020 and December 31, 2019. On a recurring basis, the Company records its marketable securities at fair value using Level 1 or Level 2 inputs as discussed in Note 2, "Fair Value Measurements". The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type at each balance sheet date are summarized in the tables below (in thousands):


	March 31, 2020
	Amortized Cost		Unrealized Holding Gains		Unrealized Holding Losses		Aggregate Fair Value
Short-term marketable securities:
U.S. government treasuries	$	272,289	$	1,391	$	—	$	273,680

Corporate debt securities⁽¹⁾	61,920		39		(193)		61,766
Commercial paper	44,267		—		—		44,267
Total short-term marketable securities	378,476		1,430		(193)		379,713
Long-term marketable securities:
U.S. government treasuries	2,525		40		—		2,565
Corporate debt securities⁽²⁾	7,153		—		(34)		7,119
Total long-term marketable securities	9,678		40		(34)		9,684
Total	$	388,154	$	1,470	$	(227)	$	389,397

__________________________________________________

(1)Unrealized holding losses on 10 securities, with an aggregate fair value of $35.7 million.

(2)Unrealized holding losses on 1 security, with an aggregate fair value of $7.1 million.


	December 31, 2019
	Amortized Cost		Unrealized Holding Gains		Unrealized Holding Losses		Aggregate Fair Value
Short-term marketable securities:
U.S. government treasuries⁽¹⁾	$	249,478	$	594	$	(2)	$	250,070
U.S. government agency securities	1,999		1		—		2,000
Corporate debt securities⁽²⁾	53,396		94		(11)		53,479
Commercial paper	30,358		—		—		30,358
Total short-term marketable securities	335,231		689		(13)		335,907
Long-term marketable securities:
U.S. government treasuries⁽³⁾	13,865		6		(2)		13,869

Corporate debt securities⁽⁴⁾	25,998		34		(15)		26,017
Total long-term marketable securities	39,863		40		(17)		39,886
Total	$	375,094	$	729	$	(30)	$	375,793

__________________________________________________

(1)Unrealized holding losses on 2 securities, with an aggregate fair value of $9.3 million.

(2)Unrealized holding losses on 4 securities, with an aggregate fair value of $25.9 million.

(3)Unrealized holding losses on 1 security, with an aggregate fair value of $10.1 million.

(4)Unrealized holding losses on 3 securities, with an aggregate fair value of $17.2 million.

As of March 31, 2020 and December 31, 2019, some of the Company’s marketable securities were in an unrealized loss position. The Company has not recognized an allowance for credit losses as of March 31, 2020 or December 31, 2019. The Company determined that it had the ability and intent to hold all marketable securities that have been in a continuous loss position until maturity or recovery. Further, these marketable securities were initially, and continue to be, held with investment grade, high credit quality institutions, and the unrealized losses are believed to be the result of the recent widespread market and interest rate impact of the COVID-19 pandemic. All marketable securities with unrealized losses as of each balance sheet date have been in a loss position for less than twelve months or the loss is not material.

The Company recorded unrealized gains on marketable securities as other comprehensive income in the three months ended March 31, 2020. As a result, the Company recorded a tax benefit of $0.1 million for the three months ended March 31, 2020 on the Condensed Consolidated Statements of Operations and Comprehensive Loss and a corresponding tax charge in other comprehensive income. During the three months ended March 31, 2019, no tax benefit was recorded on unrealized gains recorded in other comprehensive income.

All of the Company’s marketable securities have an effective maturity of less than two years.

Derivative Financial Instruments

3 Months Ended

Mar. 31, 2020

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Financial Instruments

Foreign Currency Exchange Rate Exposure

The Company uses forward foreign currency exchange contracts to hedge certain operational exposures resulting from potential changes in foreign currency exchange rates. Such exposures result from portions of the Company’s forecasted cash flows being denominated in currencies other than the U.S. dollar, primarily the Euro and British Pound. The derivative instruments the Company uses to hedge this exposure are not designated as cash flow hedges, and as a result, changes in their fair value are recorded in interest and other income, net, on the Company's Condensed Consolidated Statements of Operations and Comprehensive Loss.

The fair values of forward foreign currency exchange contracts are estimated using current exchange rates and interest rates and take into consideration the current creditworthiness of the counterparties. Information regarding the specific instruments used by the Company to hedge its exposure to foreign currency exchange rate fluctuations is provided below.

The following table summarizes the Company’s forward foreign currency exchange contracts outstanding as of March 31, 2020 and December 31, 2019, respectively (notional amounts in thousands):


Foreign Exchange Contracts	Number of Contracts	Aggregate Notional⁽¹⁾Amount in Foreign Currency	Maturity
Euros	26	2,746	Apr 2020 - Feb 2021
British Pounds	17	2,482	Apr 2020 - Feb 2021
Swiss Francs	5	34	Apr 2020 - Aug 2020
Total at March 31, 2020	48
Euros	23	1,500	Jan 2020 - Nov 2020
British Pounds	15	2,285	Jan 2020 - Jun 2020
Swiss Francs	10	129	Jan 2020 - Aug 2020
Total at December 31, 2019	48

_________________________________________________

⁽¹⁾The notional amount represents the net amount of foreign currency that will be received upon maturity of the forward contracts.

Acquisition	3 Months Ended
Acquisition	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Acquisition	Acquisition In August 2016, the Company entered into a License and Collaboration Agreement (“F-star Collaboration Agreement”) with F-star Gamma Limited (“F-star Gamma”), F-star Biotechnologische Forschungs-Und Entwicklungsges M.B.H ("F-star GmbH") and F-star Biotechnology Limited ("F-star Ltd") (collectively, “F-star”) to leverage F-star’s modular antibody technology and the Company’s expertise in the development of therapies for neurodegenerative diseases. Under the F-star Collaboration Agreement, the Company made payments to F-star totaling $11.5 million. In connection with the entry into the F-star Collaboration Agreement, the Company also purchased an option for an upfront option fee of $0.5 million (the “buy-out-option”), to acquire all of the outstanding shares of F-star Gamma pursuant to a pre-negotiated buy-out option agreement (the “Option Agreement”). In May 2018, the Company exercised the Option Agreement and entered into a Share Purchase Agreement (the “Purchase Agreement”) with the shareholders of F-star Gamma and Shareholder Representative Services LLC, pursuant to which the Company acquired all of the outstanding shares of F-star Gamma (the “Acquisition”). As a result of the Acquisition, F-star Gamma became a wholly-owned subsidiary of the Company and the Company changed the entity’s name to Denali BBB Holding Limited. In addition, the Company became a direct licensee of certain intellectual property of F-star Ltd by way of the Company’s assumption of F-star Gamma’s license agreement with F-star Ltd, dated August 24, 2016, (the “F-star Gamma License”). The Company made initial exercise payments under the Purchase Agreement and the F-star Gamma License, in the aggregate, of $17.8 million. In addition, the Company is required to make future contingent payments, to F-star Ltd and the former shareholders of F-star Gamma, up to a maximum amount of $447.0 million in the aggregate upon the achievement of certain defined preclinical, clinical, regulatory and commercial milestones. These include up to $27.0 million in preclinical contingent payments, $50.0 million in clinical contingent payments, $120.0 million in regulatory contingent payments and $250.0 million in commercial contingent payments. The amount of the contingent payments will vary based on whether F-star delivers an Fcab (constant Fc-domains with antigen-binding activity) that meets pre-defined criteria and whether the Fcab has been identified solely by the Company or solely by F-star or jointly by the Company and F-star. The Company concluded that the assets acquired and liabilities assumed upon the exercise of the Option Agreement did not meet the accounting definition of a business, and as such, the acquisition was accounted for as an asset purchase. As the transaction was accounted for as an asset purchase rather than a business combination, the Company did not recognize any contingent consideration on the acquisition date. To date, the Company has paid consideration of $19.8 million in aggregate, consisting of up-front and contingent consideration, all of which was recorded as research and development expense as incurred. No contingent consideration was recognized in the three months ended March 31, 2020 or March 31, 2019. Any future contingent consideration is expected to be recognized as incurred in research and development expense on the Condensed Consolidated Statements of Operations and Comprehensive loss. Under the F-star Collaboration Agreement, the Company is responsible for certain research costs incurred by F-star Ltd in conducting activities under an agreed development plan for each Fcab, for up to 24 months after the target Fcab is accepted. The Company's responsibility for research costs under the first development plan related to an Fcab that targets the transferrin receptor was completed during the year ended December 31, 2018. The responsibility for costs under the second development plan related to an undisclosed Fcab target commenced in February 2019. The Company recognized $0.3 million and $0.2 million in research and development expense related to the funding of F-star Ltd activities under this development plan during the three months ended March 31, 2020 and March 31, 2019, respectively.

Collaboration Agreements

3 Months Ended

Mar. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaboration Agreements

Sanofi

In October 2018, the Company entered into a Collaboration and License Agreement ("Sanofi Collaboration Agreement") with Genzyme Corporation, a wholly owned subsidiary of Sanofi S.A. ("Sanofi") pursuant to which certain small molecule CNS and peripheral RIPK1 inhibitors contributed by Sanofi and by Denali will be developed and commercialized. The Sanofi Collaboration Agreement became effective in November 2018 when the HSR requirements were satisfied at which time Sanofi paid the Company an upfront payment of $125.0 million. Under the Sanofi Collaboration Agreement, Denali is eligible to receive milestone payments from Sanofi up to approximately $1.1 billion upon achievement of certain clinical, regulatory and sales milestone events. Such milestone payments include $215.0 million in clinical milestone payments and $385.0 million in regulatory milestone payments for CNS Products, as defined, that are developed and approved in the United States, by the European Medicines Agency ("EMA") and in Japan for three indications, including Alzheimer's disease. These milestones also include $120.0 million in clinical milestone payments, $175.0 million in regulatory milestone payments and $200.0 million in commercial milestone payments for Peripheral Products, as defined, that are developed and approved in the United States, by the EMA and Japan for three indications.

Denali will share profits and losses equally with Sanofi for CNS Products sold in the United States and China, and receive variable royalties on net sales for CNS Products sold outside of the United States and China and for Peripheral Products sold worldwide.

Denali and Sanofi will jointly develop CNS Products pursuant to a global development plan. The Company will be responsible, at its own cost, for conducting Phase 1 and Phase 2 trials for CNS Products in Alzheimer’s disease and any activities required to support such clinical trials and specific for Alzheimer’s disease. Denali is conducting, at Sanofi’s cost, a Phase 1b trial for the lead CNS penetrant RIPK1 inhibitor, DNL747, in ALS. Sanofi is responsible, at its cost, for all other Phase 1 and Phase 2 trials for CNS Products, including for multiple sclerosis. Sanofi will lead the conduct of all Phase 3 and later stage development trials for CNS Products, with Sanofi and Denali funding 70% and 30% of such costs, respectively. Sanofi will also lead the commercialization activities globally for CNS Products, subject to certain options that Denali has to conduct co-commercialization activities with respect to each CNS Product in the United States and China.

Sanofi will be responsible, at its cost, for conducting activities relating to the development and commercialization of all Peripheral Products. Denali will be entitled to receive tiered royalties in the low- to mid- teen percentages on net sales of Peripheral Products.

The Company identified the following distinct performance obligations associated with the Sanofi Collaboration Agreement upon inception: the CNS program license, the Peripheral program license, the Phase 1 and Phase 2 trials for CNS Products for Alzheimer’s disease ("Alzheimer's Disease Services"), and the Phase 1b trial for DNL747 for ALS and associated activities ("Retained Activities").

The Company believes that the Sanofi Collaboration Agreement is a collaboration arrangement as defined in ASC 808. The Company also believes that Sanofi meets the definition of a customer as defined in ASC 606, Revenue From Contracts With Customers for three of the performance obligations identified at inception, but does not meet the definition of a customer for the Alzheimer's Disease Services. Further, Sanofi does not meet the definition of a customer for all Phase 3 and later stage development trials for CNS Products led by Sanofi for which Denali will fund 30% of total costs. Since ASC 808 does not address recognition and measurement, the Company looked to other accounting literature for guidance where the performance obligation does not fall under ASC 606, and determined that for the Alzheimer's Disease Services, the guidance in ASC 606 should be analogized for the recognition, measurement and reporting of this performance obligation, and for the cost sharing provisions, the Company determined that the guidance in ASC 730, Research and Development should be applied.

The transaction price at inception included upfront fixed consideration of $125.0 million. All potential future milestones and other payments were considered constrained at the inception of the Sanofi Collaboration Agreement since the Company could not conclude it was probable that a significant reversal in the amount recognized would not occur. From inception through March 31, 2020, the transaction price increased by $23.3 million, consisting of $13.3 million related to costs incurred for Retained Activities that were no longer constrained, and $10.0 million related to a milestone triggered in July 2019. During the three months ended March 31, 2020 and 2019, the transaction price increased by $0.5 million and $3.4 million, respectively, related entirely to costs incurred for Retained Activities that were no longer constrained.

The respective standalone value for each of the performance obligations has been determined by applying the SSP method and the transaction price allocated based on the relative SSP method with revenue recognition timing to be determined either by delivery or the provision of services.

The Company used an adjusted market assessment approach to estimate the selling price for the program licenses, and an expected cost plus margin approach for estimating the Alzheimer’s Disease Services and the Retained Activities. The program licenses and existing know-how were delivered on the effective date of the Sanofi Collaboration Agreement. The Alzheimer’s Disease Services and the Retained Activities are expected to be delivered over time as the services are performed. For the Alzheimer's Disease Services, revenue will be recognized over time using the input method, based on costs incurred to perform the services, since the level of costs incurred over time is thought to best reflect the transfer of services to Sanofi. For the Retained Activities, revenue will be recognized over time using the output method, based on amounts invoiced to Sanofi, since this is believed to directly correlate to the value of the services performed.

A contract liability of $3.4 million and $3.5 million was recorded on the Condensed Consolidated Balance Sheets as of March 31, 2020 and December 31, 2019, respectively. These contract liabilities relate to the portion of the Alzheimer's Disease Services performance obligation yet to be satisfied, with such amounts to be recognized over the estimated period of the services, which is expected to be several years. There was a receivable of $0.5 million and $1.2 million at March 31, 2020 and December 31, 2019, respectively, associated with the Sanofi Collaboration Agreement.

In assessing the Sanofi Collaboration Agreement, management is required to exercise considerable judgment in estimating revenue to be recognized. Management applies judgment in determining the separate performance obligations, in estimating the selling price, in determining when control was transferred to Sanofi for the licenses, and in estimating total future costs when using the input method.

Through March 31, 2020, Denali has received milestone payments of $10.0 million and has not recorded any product sales recorded under the Sanofi Collaboration Agreement.

Takeda

In January 2018, the Company entered into a Collaboration and Option Agreement ("Takeda Collaboration Agreement") with Takeda Pharmaceutical Company Limited ("Takeda"), pursuant to which the Company granted Takeda an option to develop and commercialize, jointly with the Company, certain biologic products that are enabled by Denali's blood-brain barrier ("BBB") delivery technology and intended for the treatment of neurodegenerative disorders. The programs were Denali’s ATV:BACE1/Tau and ATV:TREM2 and PTV:PGRN programs. The Takeda Collaboration Agreement became effective in February 2018, at which time Takeda paid the Company an upfront payment of $40.0 million. Takeda may pay up to an aggregate of $25.0 million with respect to each of the three programs directed to a target and based upon the achievement of certain preclinical milestone events, up to $75.0 million in total, $5.0 million of which was paid upon the Takeda Collaboration Agreement becoming effective. In February 2019, the agreement was amended to replace the ATV:BACE1/Tau program with the ATV:Tau program. The amendment did not have a material impact to the condensed consolidated financial statements.

Under the Takeda Collaboration Agreement and unless otherwise agreed jointly between both parties, Denali will be responsible, at its cost, for conducting activities relating to pre-IND development of biologic products directed to the three identified targets and enabled by its BBB delivery technology targeting TfR during the applicable research period. The period through which the option can be exercised continues for each target until the first biologic product directed to the relevant target is IND-ready or approximately five years after selection of the target, whichever is earlier.

If Takeda exercises its option with respect to a particular target, then Takeda will have the right to develop and commercialize, jointly with the Company, a specified number of biologic products enabled by its BBB delivery technology that were developed during the research period and which are directed to the relevant target. The Company will grant to Takeda a co-exclusive license under the intellectual property the Company controls related to those biologic products.

Takeda is obligated to pay Denali a $5.0 million option fee for each target for which Takeda exercises its option, up to $15.0 million in total.

In addition, if Takeda exercises its option for all three collaboration programs, Takeda may be obligated to pay Denali up to an aggregate of $407.5 million upon achievement of certain clinical milestone events and up to an aggregate of $300.0 million in regulatory milestone events relating to receipt of regulatory approval in the United States, certain European countries and Japan. Takeda may also be obligated to pay Denali up to $75.0 million per biologic product upon achievement of a certain sales-based milestone, or an aggregate of $225.0 million if one biologic product from each program achieves this milestone.

If Takeda exercises its option for a particular target, Denali and Takeda will share equally the development and commercialization costs, and, if applicable, the profits, for each collaboration program.

Pursuant to the terms of the Takeda Collaboration Agreement, the Company entered into a common stock purchase agreement (the "Stock Purchase Agreement") with Takeda on January 3, 2018, pursuant to which Takeda purchased 4,214,559 shares of Denali’s common stock (the "Shares") for an aggregate purchase price of $110.0 million. The sale of the Shares closed on February 23, 2018. The fair market value of the common stock sold to Takeda was $94.4 million, based on the closing stock price of $22.40 on the date of issuance, resulting in a $15.6 million premium paid to the Company above the fair value of the Company's common stock which was credited to contract liability in the Company's Condensed Consolidated Balance Sheets.

The Company believes that the Takeda Collaboration Agreement is a collaboration arrangement as defined in ASC 808. Further, during the research period, the Company believes that the arrangement is a contract with a customer as defined in ASC 606, Revenue From Contracts With Customers. The Takeda Collaboration Agreement and the Stock Purchase Agreement are being accounted for as one arrangement because they were entered into at the same time with interrelated financial terms.

The Company identified performance obligations during the research period consisting of the license, the development options, and joint steering committee ("JSC") participation together with the research services for each collaboration program. The license rights, JSC involvement, option and research services are considered to be a single performance obligation for each program since the research services are highly interrelated with the option and JSC involvement and will significantly modify the license. The performance obligations under each of the three programs are separate since the activities and risks under the programs are distinct.

The Company has determined that all other goods or services which are contingent upon Takeda exercising its option for each program are not considered performance obligations at the inception of the Takeda Collaboration Agreement.

The transaction price at inception included fixed consideration consisting of the upfront fee of $40.0 million, the $15.6 million premium on the sale of common stock, and the first preclinical milestone payment of $5.0 million. It also included variable consideration of $26.0 million relating to future milestones that were not constrained. The amount of variable consideration was estimated using the most likely amount method.

The remaining $44.0 million of preclinical milestones were considered constrained at the inception of the Takeda Collaboration Agreement since the Company could not conclude it is probable that a significant reversal in the amount recognized will not occur. Additionally, cost and profit sharing income, and the development and commercial milestones as outlined above, have not been considered given Takeda has not exercised its options for the development and commercial phases for any program. No change in the transaction price has been recorded since inception. This will be reassessed at each reporting period.

The transaction price has been ascribed in its entirety to the three performance obligations identified in the research term of the Takeda Collaboration Agreement.

Revenue is recognized when, or as, the Company satisfies its performance obligations by transferring the promised services to Takeda. Revenue is being recognized over time using the input method, based on costs incurred to perform the research services, since the level of costs incurred over time is thought to best reflect the transfer of services to Takeda. There were no material changes in estimates during the three months ended March 31, 2020 or March 31, 2019.

A contract liability of $56.0 million and $59.0 million is recorded on the Condensed Consolidated Balance Sheets as of March 31, 2020 and December 31, 2019, respectively. This contract liability relates to the three performance obligations identified, with such amounts to be recognized over the estimated period of the pre-IND research services, which is expected to be several years. There was no receivable as of March 31, 2020 or December 31, 2019, related to the Takeda Collaboration Agreement.

Revenue recognized relating to future milestone payments of $3.3 million and $2.4 million, which the Company concluded is probable that a significant reversal in the amount recognized will not occur, is presented net in the contract liability on the Condensed Consolidated Balance Sheets as of March 31, 2020 and December 31, 2019, respectively.

In assessing the Takeda Collaboration Agreement, management is required to exercise considerable judgment in estimating revenue to be recognized. Management applies judgment in determining the separate performance obligations in the research period, estimating variable consideration, and estimating total future costs when using the input method. There is some increase in the judgment required in estimating the timing of future costs due to the COVID-19 pandemic. This is because it is challenging to predict the duration and extent of the impact of the COVID-19 pandemic on the third-party service providers assisting with the Company's ATV:Tau, ATV:TREM2 and PTV:PGRN programs. This may impact the split between current and non-current contract liability on the Condensed Consolidated Balance Sheet in the future.

Through March 31, 2020, Denali has received $15.0 million in preclinical milestone payments from Takeda and has not recorded any product sales under the Takeda Collaboration Agreement.

Collaboration Revenue

Revenue disaggregated by collaboration agreement and performance obligation is as follows (in thousands):


	Three Months Ended March 31,
	2020		2019
Takeda Collaboration Agreement⁽¹⁾	$	3,018	$	682
Sanofi Collaboration Agreement


Alzheimer's Disease Services⁽¹⁾	52		94
Retained Activities	534		3,429
Total Sanofi Collaboration Revenue	586		3,523
Total Collaboration Revenue	$	3,604	$	4,205

_________________________________________________

(1)Amounts represent revenue recognized during the period that was included in the contract liability balance at the beginning of the period.

License Agreements	3 Months Ended
License Agreements	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License Agreements	License Agreements Genentech In June 2016, the Company entered into an Exclusive License Agreement with Genentech, Inc. (“Genentech”). The agreement gives the Company access to Genentech’s LRRK2 inhibitor small molecule program for Parkinson’s disease. Under the agreement, Genentech granted the Company (i) an exclusive, worldwide, sublicensable license under Genentech’s rights to certain patents and patent applications directed to small molecule compounds which bind to and inhibit LRRK2 and (ii) a non-exclusive, worldwide, sublicensable license to certain related know-how, in each case, to develop and commercialize certain compounds and licensed products incorporating any such compound. The Company may owe Genentech milestone payments upon the achievement of certain development, regulatory, and commercial milestones, up to a maximum of $315.0 million in the aggregate. These milestones include up to $37.5 million in clinical milestone payments, $102.5 million in regulatory milestone payments and $175.0 million in commercial milestone payments. In addition, the Company may owe royalties on net sales of licensed products ranging from low to high single-digit percentages. To date, the Company has paid Genentech $12.5 million in the aggregate, including an upfront fee, a technology transfer fee and a clinical milestone payment, all of which was recorded as research and development expense as incurred. No amounts were recorded in the three months ended March 31, 2020 or 2019.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Lease Obligations

In May 2018, the Company entered into an amendment to its operating lease for its former corporate headquarters in South San Francisco (the "Headquarters Lease Amendment") to relocate and expand its headquarters to 148,020 rentable square feet in a building in South San Francisco, California (the "New Premises"). The Headquarters Lease Amendment has a contractual term of ten years from the legal commencement date, which was April 1, 2019, when the building was ready for occupancy. For accounting purposes, the lease commencement date was determined to be August 1, 2018, which was the date at which the Company was deemed to have obtained control over the property. The Company has an option to extend the lease term for a period of ten years by giving the landlord written notice of the election to exercise the option at least nine months, but not more than twelve months, prior to the expiration of the Headquarters Lease Amendment lease term. The Company determined that this renewal was not reasonably certain at lease inception.

The Headquarters Lease Amendment provides for monthly base rent amounts escalating over the term of the lease. In addition, the Headquarters Lease Amendment provided a tenant improvement allowance ("TIA") of up to $25.9 million, which was fully utilized, of which $4.4 million will be repaid to the landlord in the form of additional monthly rent. This is recorded as leasehold improvement assets and an offset to the lease ROU asset on the Condensed Consolidated Balance Sheets as of March 31, 2020 and December 31, 2019. The Company is also required to pay the operating expenses for the New Premises, such as taxes and insurance, which are treated as variable lease payments.

Management exercised judgment in applying the requirements of ASC 842, including the determination as to whether certain contracts contain a lease and for the Headquarters Lease Amendment, the discount rate used to determine the measurement of the lease liability. As the implicit rate of the Headquarters Lease Amendment was not known, the Company estimated a 9.0% discount rate, which was management’s estimate of the Company’s incremental borrowing rate. To estimate the incremental borrowing rate, management considered observable debt yields of comparable market instruments, as well as benchmarks within the Headquarters Lease Amendment that may be indicative of the rate implicit in the lease.

Total operating lease costs, including variable and short-term lease costs, was $2.6 million and $2.3 million for the three months ended March 31, 2020 and 2019, respectively.

Operating lease liabilities are calculated as the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. As of March 31, 2020, the weighted average remaining lease term was 9.1 years and the weighted average discount rate used to determine the operating lease liability was 9.0%. Cash paid for amounts included in the measurement of lease liabilities for the three months ended March 31, 2020 and March 31, 2019 of $2.2 million and $0.7 million, respectively, was included in net cash used in operating activities in the Company's Condensed Consolidated Statements of Cash Flows.

The following table reconciles the undiscounted cash flows for the next five years and total of the remaining years to the operating lease liabilities recorded in the Condensed Consolidated Balance Sheet as of March 31, 2020 (in thousands):


Year Ended December 31:
2020 (nine months)	$	7,572
2021	10,391
2022	10,731
2023	11,083
2024	11,447
Thereafter	54,074
Total undiscounted lease payments	105,298
Present value adjustment	(33,384)
Net operating lease liabilities	$	71,914

In October 2018, the Company entered into a sublease agreement ("Sublease Agreement") to sublease approximately 36,835 rentable square feet of space in its New Premises. The Sublease Agreement has a term of five years from the commencement date of April 12, 2019 and provides for the Company to receive monthly base rent amounts escalating over the term of the lease. The Company also passes through a portion of the operating expenses, such as taxes and insurance for the New Premises to the sublessee, which are treated as variable sublease income. Total sublease income, including rent and variable sublease cost reimbursements, was $0.9 million for three months ended March 31, 2020, respectively. There was no sublease income for the three months ended March 31, 2019.

The following table details the future undiscounted cash inflows relating to the Sublease Agreement as of March 31, 2020 (in thousands):


Year Ended December 31:
2020 (nine months)	$	2,146
2021	2,925
2022	3,009
2023	3,096
2024	876
Thereafter	—
Total undiscounted sublease receipts	$	12,052

Indemnification

In the ordinary course of business, the Company may provide indemnifications of varying scope and terms to vendors, lessors, business partners, board members, officers, and other parties with respect to certain matters, including, but not limited to, losses arising out of breach of such agreements, services to be provided by the Company, negligence or willful misconduct of the Company, violations of law by the Company, or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with directors and certain officers and employees that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or employees. No demands have been made upon the Company to provide indemnification under such agreements, and thus, there are no claims that the Company is aware of that could have a material effect on the Company’s Condensed Consolidated Balance Sheets, Condensed Consolidated Statements of Operations and Comprehensive Loss, or Condensed Consolidated Statements of Cash Flows.

Commitments

Effective September 2017, the Company entered into a Development and Manufacturing Services Agreement as amended (“DMSA”) with Lonza Sales AG (“Lonza”) for the development and manufacture of biologic products. Under the DMSA, the Company will execute purchase orders based on project plans authorizing Lonza to provide development and manufacturing services with respect to certain of the Company's antibody and enzyme products, and will pay for the services provided and batches delivered in accordance with the DMSA and project plan. Unless earlier terminated, the DMSA will expire on September 6, 2022.

As of March 31, 2020 and December 31, 2019, the Company had open non-cancellable purchase orders for biological product development and manufacturing costs totaling $14.6 million and $21.2 million respectively. The activities under these purchase orders are expected to be completed by March 2026. As of March 31, 2020 and December 31, 2019, the Company had total non-cancellable purchase commitments under the DMSA of $7.6 million and $11.2 million, respectively.

During the three months ended March 31, 2020 and 2019, the Company incurred costs of $1.0 million and $3.6 million, respectively, and made payments of $3.2 million and $2.6 million, respectively, for the development and manufacturing services rendered under the DMSA.

Stock-Based Awards

3 Months Ended

Mar. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock-Based Awards

2017 Equity Incentive Plan

In December 2017, the Company adopted the 2017 Equity Incentive Plan (the “2017 Plan”), which initially reserved approximately 6.4 million shares of common stock for the issuance of stock options, restricted stock and other stock awards, to employees, non-employee directors, and consultants under terms and provisions established by the Board of Directors and approved by the stockholders. The 2017 Plan provides that the number of shares reserved and available for issuance under the 2017 Plan will automatically increase each year on January 1st, by the least of (i) 10.0 million shares, (ii) 5% of the outstanding shares on the last day of the immediately preceding fiscal year, or (iii) such number of shares determined by the administrator of the 2017 Plan. In January 2020, common stock available for issuance under the 2017 Plan was increased by approximately 4.8 million shares as a result of this automatic increase provision.

Awards granted under the 2017 Plan expire no later than ten years from the date of grant. For stock options, the option price shall not be less than 100% of the estimated fair value of the Company's common stock on the day of grant. Options granted typically vest over a four-year period but may be granted with different vesting terms.

2015 Stock Incentive Plan

In May 2015, the Company adopted the 2015 Stock Incentive Plan (the “2015 Plan”), which as amended, reserved approximately 8.3 million shares of common stock for the issuance of stock options, restricted stock and other stock awards, to employees, non-employee directors, and consultants under terms and provisions established by the Board of Directors and approved by the stockholders. Awards granted under the 2015 Plan expire no later than ten years from the date of grant. For stock options, the option price shall not be less than 100% of the estimated fair value of the Company's common stock on the day of grant. Options granted typically vest over a four-year period but may be granted with different vesting terms.

Upon adoption of the 2017 Plan, no new awards or grants are permitted under the 2015 Plan, and the approximately 0.2 million shares that were then unissued and available for future award under the 2015 Plan became available under the 2017 Plan. The 2015 Plan will continue to govern restricted stock awards and option awards previously granted thereunder.

As of March 31, 2020 and December 31, 2019, there were approximately 4.5 million and 3.4 million shares of common stock, respectively, available for the Company to grant under the 2017 Plan.

Stock Option Activity

The following table summarizes option award activity under the 2017 Plan and the 2015 Plan:


	Number of Options	Weighted- Average Exercise Price		Weighted- Average remaining contractual life (years)	Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2019	11,640,734	$	12.96	7.79
Options granted	2,998,584	24.63
Options exercised	(259,569)	7.57
Options forfeited	(130,071)	18.02
Balance at March 31, 2020	14,249,678	$	15.47	8.03	$	64,492
Options vested and expected to vest at March 31, 2020	12,504,946	$	17.53	8.40	$	35,128
Options exercisable at March 31, 2020	4,729,113	$	12.63	7.42	$	29,163

Aggregate intrinsic value represents the difference between the fair value of the Company's common stock and the exercise price of outstanding options. The total intrinsic value of options exercised for the three months ended March 31, 2020 and 2019 was $3.7 million and $3.3 million, respectively. During the three months ended March 31, 2020 and 2019, the weighted-average grant date fair value of the vested options was $11.23 and $11.82 per share, respectively. The weighted-average grant date fair value of all options granted during the three months ended March 31, 2020 and 2019 was $14.73 and $11.60 per share, respectively.

Stock Options Granted to Employees with Service-Based Vesting

The estimated fair value of stock options granted to employees were calculated using the Black-Scholes option-pricing model using the following assumptions:


	Three Months Ended March 31,
	2020	2019
Expected term (in years)	6.08	6.08
Volatility	65.2% - 65.6%	69.3% - 69.4%
Risk-free interest rate	0.7% - 1.7%	2.5% - 2.6%
Dividend yield	—	—

Expected Term: The expected term represents the period that the options granted are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term).

Expected Volatility: The Company uses an average historical stock price volatility of comparable public companies within the biotechnology and pharmaceutical industry that were deemed to be representative of future stock price trends as the Company does not have sufficient trading history for its common stock. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available.

Risk-Free Interest Rate: The Company based the risk-free interest rate over the expected term of the options based on the constant maturity rate of U.S. Treasury securities with similar maturities as of the date of the grant.

Expected Dividend Yield: The Company has not paid and does not anticipate paying any dividends in the near future. Therefore, the expected dividend yield was zero.

Performance and Market Contingent Stock Options Granted to Employees

In August and November 2015, the Board of Directors granted approximately 1.6 million and 0.1 million shares of performance- and market- contingent awards to members of the senior management team, respectively. These awards have an exercise price of $0.68 per share.

These awards have two separate market triggers for vesting based upon either (i) the successful achievement of stepped target closing prices on a national securities exchange for 90 consecutive trading days later than 180 days after the Company’s initial public offering for its common stock, or (ii) stepped target prices for a change in control transaction. In the event that neither of these market triggers are achieved by the specified timelines, such awards will terminate with respect to that portion of the shares. General and administrative expense of $0.1 million was recognized associated with these performance- and market- contingent awards for the three months ended March 31, 2020. The remaining expense for these awards, to be recognized using the accelerated attribution method, is $0.2 million, which will be recognized over the remaining derived service period of approximately six months.

The Company used a lattice model with a Monte Carlo simulation to value these stock options. This valuation methodology utilized the estimated fair value of the Company’s common stock on grant date and several key assumptions, including expected volatility of the Company’s stock price based on comparable public companies, risk-free rates of return and expected dividend yield.

Stock Options Granted to Non-Employees with Service-Based Vesting Valuation Assumptions

Stock-based compensation related to stock options granted to non-employees is recognized as the stock options are earned. Prior to the adoption of ASU 2018-07 during the third quarter of 2018, the unvested options granted to non-employees were revalued using the Company's estimate of fair value on each reporting date. Subsequent to the adoption of ASU 2018-07, existing stock options granted to non-employees are no longer revalued, and the estimated fair value of new stock options granted to non-employees is calculated on the date of grant and not remeasured, similar to stock options granted to employees.

Restricted Stock Activity

Under the 2017 Plan, the Company may grant restricted stock awards ("RSAs"), which represent restricted shares of issued common stock for which the recipient's rights in the stock are restricted until the shares are vested, and restricted stock units ("RSUs"), which represent a commitment to issue shares of common stock in the future upon vesting. The fair value of restricted stock underlying the RSAs and RSUs is determined based on the closing market price of the Company's common stock on the date of grant.

Aggregated information regarding RSAs and RSUs granted under the 2017 Plan for the three months ended March 31, 2020 is summarized below:


	Share Awards & Units	Weighted-Average Fair Value at Date of Grant per Share
Unvested at December 31, 2019	882,636	$	18.67
Granted	868,500	24.50
Vested and released	(91,839)	18.60
Forfeited	(21,313)	18.34
Unvested at March 31, 2020	1,637,984	$	21.75
Expected to vest - March 31, 2020	1,637,984	$	21.75

The aggregate intrinsic value of RSUs is calculated as the closing price per share of the Company's common stock on the last trading day of the fiscal period, multiplied by the number of RSUs expected to vest. The total intrinsic value of RSUs expected to vest was $28.7 million as of March 31, 2020. During the three months ended March 31, 2020 and 2019, the weighted-average grant-date fair value of RSUs granted was $24.50 and $18.27, respectively. The total fair value of RSAs and RSUs that vested during the three months ended March 31, 2020 and 2019, was $2.1 million and $7.4 million, respectively.

Employee Stock Purchase Plan

In December 2017, the Company adopted the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which initially reserved 1.0 million shares of common stock for employee purchases under terms and provisions established by the Board of Directors. The 2017 ESPP provides that the number of shares reserved and available for issuance under the 2017 ESPP will automatically increase each year on January 1st, by the least of (i) 2.0 million shares, (ii) 1% of the outstanding shares on the last day of the immediately preceding fiscal year, or (iii) such number of shares determined by the administrator of the 2017 Plan. In January 2020, common stock available for issuance under the 2017 ESPP was increased by approximately 1.0 million shares as a result of this automatic increase provision.

Under the 2017 ESPP, employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of common stock on the first trading day of each offering period or on the exercise date. The 2017 ESPP provides for consecutive, overlapping 12-month offering periods. The offering periods are scheduled to start on the first trading day on or after May 31 or November 30 of each year, except for the first offering period which commenced on December 8, 2017, the first trading day after the effective date of the Company’s registration statement. Contributions under the 2017 ESPP are limited to a maximum of 15% of an employee's eligible compensation. During the three months ended March 31, 2020 and 2019, the Company did not issue any shares of common stock under the 2017 ESPP.

Stock-Based Compensation Expense

The Company’s results of operations include expenses relating to stock-based compensation as follows (in thousands):


	Three Months Ended March 31,
	2020		2019
Research and development	$	6,054	$	3,982
General and administrative	4,731		2,892
Total	$	10,785	$	6,874

As of March 31, 2020, total unamortized stock-based compensation expense related to employee and non-employee awards was $129.5 million. The weighted-average period over which such stock-based compensation expense will be recognized is approximately 3.2 years.

Net Loss Per Share

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Net Loss Per Share

Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share for all periods as the inclusion of all potential shares of common stock outstanding would have been anti-dilutive.

Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:


	Three Months Ended March 31,
	2020	2019
Options issued and outstanding and ESPP shares issuable	14,530,378	12,202,568
Restricted shares subject to future vesting	1,637,984	524,359
Early exercised common stock subject to future vesting	—	88,550
Total	16,168,362	12,815,477

Significant Accounting Policies (Policies)	3 Months Ended
Significant Accounting Policies (Policies)	Mar. 31, 2020
Accounting Policies [Abstract]
Organization and Description of Business	Organization and Description of Business Denali Therapeutics Inc. ("Denali" or the “Company”) is a biopharmaceutical company, incorporated in Delaware, that discovers and develops therapeutics to defeat neurodegenerative diseases. The Company is headquartered in South San Francisco, California.
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial information and the instructions to Form 10-Q and Article 10 of SEC Regulation S-X for interim financial information. These unaudited condensed consolidated financial statements and notes should be read in conjunction with the audited consolidated financial statements and notes thereto contained in the Annual Report on Form 10-K for the year ended December 31, 2019, as filed with the Securities and Exchange Commission on February 27, 2020 (the "2019 Annual Report on Form 10-K"). The Condensed Consolidated Balance Sheet as of December 31, 2019 was derived from the audited annual consolidated financial statements as of the period then ended. Certain information and footnote disclosures typically included in the Company's annual consolidated financial statements have been condensed or omitted. The accompanying unaudited condensed consolidated financial statements reflect all adjustments that, in the opinion of management, are necessary for a fair statement of the results of the interim periods presented. All such adjustments are of a normal recurring nature except for the impacts of adopting new accounting standards discussed below. These interim financial results are not necessarily indicative of results expected for the full fiscal year or for any subsequent interim period.
Principles of Consolidation	Principles of Consolidation These unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation. For the Company and its subsidiary, the functional currency has been determined to be U.S. dollars. Monetary assets and liabilities denominated in foreign currency are remeasured at period-end exchange rates. Non-monetary assets and liabilities denominated in foreign currencies are remeasured at historical rates. Foreign currency transaction gains and losses resulting from remeasurement are recognized in interest and other income, net in the Condensed Consolidated Statements of Operations and Comprehensive Loss.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires the Company to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities at the date of the condensed consolidated financial statements, as well as the reported amounts of expenses during the reporting period. Actual results could differ from those estimates, and such differences could be material to the Condensed Consolidated Balance Sheets and Statements of Operations and Comprehensive Loss.
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 significant concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities and forward foreign currency exchange contracts. Substantially all of the Company’s cash and cash equivalents are deposited in accounts with financial institutions that management believes are of high credit quality. Such deposits have and will continue to exceed federally insured limits. The Company maintains its cash with accredited financial institutions and accordingly, such funds are subject to minimal credit risk. The Company’s investment policy limits investments to certain types of securities issued by the U.S. government, its agencies and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash, cash equivalents and marketable securities and issuers of marketable securities to the extent recorded on the Condensed Consolidated Balance Sheets. As of March 31, 2020 and December 31, 2019, the Company had no off-balance sheet concentrations of credit risk. The Company is exposed to counterparty credit risk on all of its derivative financial instruments. The Company has established and maintains strict counterparty credit guidelines and enters into hedges only with financial institutions that are investment grade or better to minimize the Company’s exposure to potential defaults. The Company does not require collateral to be pledged under these agreements. The Company is subject to a number of risks similar to other early-stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of current or future preclinical testing or clinical trials, its reliance on third parties to conduct its clinical trials, the need to obtain regulatory and marketing approvals for its product candidates, competitors developing new technological innovations, 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 any license or collaboration agreements, and the need to secure and maintain adequate manufacturing arrangements with third parties. If the Company does not successfully commercialize or partner any of its product candidates, it will be unable to generate product revenue or achieve profitability. The COVID-19 pandemic has caused increased risk and uncertainty for the Company. Credit risk associated with investments in securities may increase if any institution with which the Company has an investment is significantly impacted by the COVID-19 pandemic. As of March 31, 2020, the Company has not realized any losses on its cash deposits or investments. Further, COVID-19 may impact the timelines and progress of the Company's preclinical activities and clinical trials, and may impact its ability to raise capital in the near term.
Segments	Segments The Company has one operating segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with original maturities of 90 days or less at the date of purchase to be cash and cash equivalents. Cash equivalents are reported at fair value. The Company’s restricted cash consists of the letter of credit for the Company’s headquarters building lease, and is included within other non-current assets on the accompanying Condensed Consolidated Balance Sheets.
Marketable Securities	Marketable Securities The Company generally invests its excess cash in money market funds and investment grade short to intermediate-term fixed income securities. Such investments are included in cash and cash equivalents, short-term marketable securities, or long-term marketable securities on the Condensed Consolidated Balance Sheets, are considered available-for-sale, and reported at fair value with net unrealized gains and losses included as a component of stockholders’ equity. The Company classifies investments in securities with remaining maturities of less than one year, or where its intent is to use the investments to fund current operations or to make them available for current operations, as short-term investments. The Company classifies investments in securities with remaining maturities of over one year as long-term investments. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in interest and other income, net in the Condensed Consolidated Statements of Operations and Comprehensive Loss. Realized gains and losses and declines in value determined to be due to credit losses on marketable securities, if any, are included in interest and other income, net. The Company periodically evaluates the need for an allowance for credit losses. This evaluation consists of several qualitative and quantitative factors, including whether it has plans to sell the security, whether it is more likely than not it will be required to sell any marketable securities before recovery of its amortized cost basis, and if the entity has the ability and intent to hold the security to maturity, and the portion of any unrealized loss that is the result of a credit loss. Factors considered in making these evaluations include quoted market prices, recent financial results and operating trends, implied values from any recent transactions or offers of investee securities, credit quality of debt instrument issuers, expected cash flows from securities, other publicly available information that may affect the value of the marketable security, duration and severity of the decline in value, and the Company's strategy and intentions for holding the marketable security.
Accounts Receivable	Accounts ReceivableAccounts receivable are included within prepaid expenses and other current assets on the Condensed Consolidated Balance Sheets. The accounts receivable balance represents amounts receivable from the Company's collaboration partners, net of an allowance for credit losses, if required.
Derivatives and Hedging Activities	Derivatives and Hedging ActivitiesThe Company measures its derivative instruments at fair value, and accounts them as either assets or liabilities included within prepaid assets and other current assets and other accruals and current liabilities, respectively, on the Condensed Consolidated Balance Sheets. Derivatives are adjusted to fair value through interest and other income, net in the Condensed Consolidated Statements of Operations and Comprehensive Loss.
Leases	Leases The Company adopted Accounting Standards Update ("ASU") No. 2016-02, Leases as of January 1, 2019. A determination is made as to whether an arrangement is a lease at inception. A right-of-use (“ROU”) asset and operating lease liability is recognized for identified operating leases in the Condensed Consolidated Balance Sheets. ROU assets represent the Company’s right to use the underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments due over the lease term, with the ROU assets adjusted for lease incentives received. When determining the present value of lease payments, the Company uses its incremental borrowing rate on the date of lease commencement, or the rate implicit in the lease, if known. The Company does not assume renewals in its determination of the lease term unless the renewals are deemed by management to be reasonably certain at lease inception. Leases with an initial term of 12 months or less are not recorded on the balance sheet, unless they include an option to purchase the underlying asset that the Company is reasonably certain to exercise. The Company recognizes lease expenses on a straight-line basis over the lease term. The Company has leases with lease and non-lease components, which the Company has elected to account for as a single lease component.
Revenue Recognition	Revenue Recognition License and Collaboration Revenue The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (“ASC 808”) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and, therefore, within the scope of Topic 606. For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to Topic 606. The accounting treatment pursuant to Topic 606 is outlined below. The terms of licensing and collaboration agreements entered into typically include payment of one or more of the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply and research and development services; and royalties on net sales of licensed products. Each of these payments results in license, collaboration and other revenue, except for revenues from royalties on net sales of licensed products, which are classified as royalty revenue. The core principle of Topic 606 is to recognize revenue when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Amounts received prior to satisfying the revenue recognition criteria are recorded as contract liabilities in the Company’s Condensed Consolidated Balance Sheets. If the related performance obligation is expected to be satisfied within the next twelve months this will be classified in current liabilities. Amounts recognized as revenue prior to the Company having an unconditional right (other than a right that is conditioned only on the passage of time) to receipt are recorded as contract assets in the Company's Condensed Consolidated Balance Sheets. If the Company expects to have an unconditional right to receive the consideration in the next twelve months, this will be classified in current assets. A net contract asset or liability is presented for each contract with a customer. At contract inception, the Company assesses the goods or services promised in a contract with a customer and identifies those distinct goods and services that represent a performance obligation. A promised good or service may not be identified as a performance obligation if it is immaterial in the context of the contract with the customer, if it is not separately identifiable from other promises in the contract (either because it is not capable of being separated or because it is not separable in the context of the contract), or if the performance obligation does not provide the customer with a material right. The Company considers the terms of the contract to determine the transaction price. The transaction price is the amount of consideration to which the Company expects to be entitled in exchange for transferring promised goods or services to a customer. The consideration promised in a contract with a customer may include fixed amounts, variable amounts, or both. Variable consideration will only be included in the transaction price when it is not considered constrained, which is when it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur. If it is determined that multiple performance obligations exist, the transaction price is allocated at the inception of the agreement to all identified performance obligations based on the relative standalone selling prices ("SSP"). The relative SSP for each deliverable is estimated using external sourced evidence if it is available. If external sourced evidence is not available, the Company uses its best estimate of the SSP for the deliverable. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset, which for a service is considered to be as the services are received and used. The Company recognizes revenue over time by measuring the progress toward complete satisfaction of the relevant performance obligation using an appropriate input or output method based on the nature of the service promised to the customer. After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the transaction price is allocated to the performance obligations on the same basis as at contract inception. Management may be required to exercise considerable judgment in estimating revenue to be recognized. Judgment is required in identifying performance obligations, estimating the transaction price, estimating the SSP of identified performance obligations, which may include forecasted revenue, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success, and estimating the progress towards satisfaction of performance obligations.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is composed of net loss and certain changes in stockholders’ equity (deficit) that are excluded from net loss, primarily unrealized gains or losses on the Company’s marketable securities.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.
Recently Issued and Recently Adopted Accounting Pronouncements	Recently Issued Accounting Pronouncement In December 2019, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. 2019-12, Income Taxes (Topic 740) Simplifying the Accounting for Income Taxes. ASU No. 2019-12 modifies ASC 740 to simplify several aspects of accounting for income taxes, including eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation. The guidance is effective for fiscal years beginning after December 15, 2020 and interim periods within those fiscal years, with early adoption permitted, and is required to be adopted prospectively, with the exception of certain specific amendments. The Company is currently assessing the impact of this ASU on its Condensed Consolidated Financial Statements. Recently Adopted Accounting Pronouncement In June 2016, the FASB issued Accounting Standards Update No. 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments. ASU 2016-13 requires measurement and recognition of expected credit losses for financial assets. In April 2019, the FASB issued clarification to ASU 2016-13 within ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments-Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments. The Company adopted this standard as of January 1, 2020 using a modified retrospective approach. Adoption of the standard did not have a material impact on the Condensed Consolidated Financial Statements.

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Assets Measured at Fair Value

Assets and liabilities measured at fair value at each balance sheet date are as follows (in thousands):


	March 31, 2020
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	92,160	$	—	$	—	$	92,160
U.S. government treasuries	84,996		—		—		84,996
Commercial paper	—		2,996		—		2,996
Short-term marketable securities:
U.S. government treasuries	273,680		—		—		273,680

Corporate debt securities	—		61,766		—		61,766
Commercial paper	—		44,267		—		44,267
Long-term marketable securities:
U.S. government treasuries	2,565		—		—		2,565

Corporate debt securities	—		7,119		—		7,119

Total	$	453,401	$	116,148	$	—	$	569,549
Liabilities:
Foreign currency derivative contracts	$	—	$	141	$	—	$	141
Total	$	—	$	141	$	—	$	141


	December 31, 2019
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	54,163	$	—	$	—	$	54,163
U.S. government treasuries	15,989		—		—		15,989
Short-term marketable securities:
U.S. government treasuries	250,070		—		—		250,070
U.S. government agency securities	—		2,000		—		2,000
Corporate debt securities	—		53,479		—		53,479
Commercial paper	—		30,358		—		30,358
Long-term marketable securities:
U.S. government treasuries	13,869		—		—		13,869
Corporate debt securities	—		26,017		—		26,017
Foreign currency derivative contracts	—		85		—		85
Total	$	334,091	$	111,939	$	—	$	446,030
Liabilities:
Foreign currency derivative contracts	$	—	$	8	$	—	$	8
Total	$	—	$	8	$	—	$	8

Cash and Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2020

Cash and Cash Equivalents [Abstract]

Schedule of Cash and Cash Equivalents


	March 31,			December 31,			March 31,			December 31,
			2020			2019			2019			2018
Cash and cash equivalents	$	207,537		$	79,449		$	39,661		$	77,123
Restricted cash included within other non-current assets	1,500			1,500			1,500			1,500
Total cash, cash equivalents, and restricted cash	$	209,037		$	80,949		$	41,161		$	78,623

Schedule of Restricted Cash and Cash Equivalents


	March 31,			December 31,			March 31,			December 31,
			2020			2019			2019			2018
Cash and cash equivalents	$	207,537		$	79,449		$	39,661		$	77,123
Restricted cash included within other non-current assets	1,500			1,500			1,500			1,500
Total cash, cash equivalents, and restricted cash	$	209,037		$	80,949		$	41,161		$	78,623

Summary of Available for Sale Securities

The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type at each balance sheet date are summarized in the tables below (in thousands):


	March 31, 2020
	Amortized Cost		Unrealized Holding Gains		Unrealized Holding Losses		Aggregate Fair Value
Short-term marketable securities:
U.S. government treasuries	$	272,289	$	1,391	$	—	$	273,680

Corporate debt securities⁽¹⁾	61,920		39		(193)		61,766
Commercial paper	44,267		—		—		44,267
Total short-term marketable securities	378,476		1,430		(193)		379,713
Long-term marketable securities:
U.S. government treasuries	2,525		40		—		2,565
Corporate debt securities⁽²⁾	7,153		—		(34)		7,119
Total long-term marketable securities	9,678		40		(34)		9,684
Total	$	388,154	$	1,470	$	(227)	$	389,397

__________________________________________________

(1)Unrealized holding losses on 10 securities, with an aggregate fair value of $35.7 million.

(2)Unrealized holding losses on 1 security, with an aggregate fair value of $7.1 million.


	December 31, 2019
	Amortized Cost		Unrealized Holding Gains		Unrealized Holding Losses		Aggregate Fair Value
Short-term marketable securities:
U.S. government treasuries⁽¹⁾	$	249,478	$	594	$	(2)	$	250,070
U.S. government agency securities	1,999		1		—		2,000
Corporate debt securities⁽²⁾	53,396		94		(11)		53,479
Commercial paper	30,358		—		—		30,358
Total short-term marketable securities	335,231		689		(13)		335,907
Long-term marketable securities:
U.S. government treasuries⁽³⁾	13,865		6		(2)		13,869

Corporate debt securities⁽⁴⁾	25,998		34		(15)		26,017
Total long-term marketable securities	39,863		40		(17)		39,886
Total	$	375,094	$	729	$	(30)	$	375,793

__________________________________________________

(1)Unrealized holding losses on 2 securities, with an aggregate fair value of $9.3 million.

(2)Unrealized holding losses on 4 securities, with an aggregate fair value of $25.9 million.

(3)Unrealized holding losses on 1 security, with an aggregate fair value of $10.1 million.

(4)Unrealized holding losses on 3 securities, with an aggregate fair value of $17.2 million.

Derivative Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2020

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Summary of Forward Foreign Currency Exchange Purchase Contracts Outstanding

The following table summarizes the Company’s forward foreign currency exchange contracts outstanding as of March 31, 2020 and December 31, 2019, respectively (notional amounts in thousands):


Foreign Exchange Contracts	Number of Contracts	Aggregate Notional⁽¹⁾Amount in Foreign Currency	Maturity
Euros	26	2,746	Apr 2020 - Feb 2021
British Pounds	17	2,482	Apr 2020 - Feb 2021
Swiss Francs	5	34	Apr 2020 - Aug 2020
Total at March 31, 2020	48
Euros	23	1,500	Jan 2020 - Nov 2020
British Pounds	15	2,285	Jan 2020 - Jun 2020
Swiss Francs	10	129	Jan 2020 - Aug 2020
Total at December 31, 2019	48

_________________________________________________

⁽¹⁾The notional amount represents the net amount of foreign currency that will be received upon maturity of the forward contracts

- Definition

Tabular disclosure of pertinent information about a derivative or group of derivatives on a disaggregated basis, such as for individual instruments, or small groups of similar instruments. May include a combination of the type of instrument, risks being hedged, notional amount, hedge designation, related hedged item, inception date, maturity date, or other relevant item.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-Name Accounting Standards Codification
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Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

Collaboration Agreements (Tables)

3 Months Ended

Mar. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Collaboration Revenue

Revenue disaggregated by collaboration agreement and performance obligation is as follows (in thousands):


	Three Months Ended March 31,
	2020		2019
Takeda Collaboration Agreement⁽¹⁾	$	3,018	$	682
Sanofi Collaboration Agreement


Alzheimer's Disease Services⁽¹⁾	52		94
Retained Activities	534		3,429
Total Sanofi Collaboration Revenue	586		3,523
Total Collaboration Revenue	$	3,604	$	4,205

_________________________________________________

(1)Amounts represent revenue recognized during the period that was included in the contract liability balance at the beginning of the period.

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Operating Lease Maturity, Payments


Year Ended December 31:
2020 (nine months)	$	7,572
2021	10,391
2022	10,731
2023	11,083
2024	11,447
Thereafter	54,074
Total undiscounted lease payments	105,298
Present value adjustment	(33,384)
Net operating lease liabilities	$	71,914

Operating Lease Maturity, Receivable

The following table details the future undiscounted cash inflows relating to the Sublease Agreement as of March 31, 2020 (in thousands):


Year Ended December 31:
2020 (nine months)	$	2,146
2021	2,925
2022	3,009
2023	3,096
2024	876
Thereafter	—
Total undiscounted sublease receipts	$	12,052

Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 2020

Share-based Payment Arrangement [Abstract]

Summary of Stock Option Activity

The following table summarizes option award activity under the 2017 Plan and the 2015 Plan:


	Number of Options	Weighted- Average Exercise Price		Weighted- Average remaining contractual life (years)	Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2019	11,640,734	$	12.96	7.79
Options granted	2,998,584	24.63
Options exercised	(259,569)	7.57
Options forfeited	(130,071)	18.02
Balance at March 31, 2020	14,249,678	$	15.47	8.03	$	64,492
Options vested and expected to vest at March 31, 2020	12,504,946	$	17.53	8.40	$	35,128
Options exercisable at March 31, 2020	4,729,113	$	12.63	7.42	$	29,163

Summary of Assumptions Used for Estimating the Fair Value of Stock Granted

The estimated fair value of stock options granted to employees were calculated using the Black-Scholes option-pricing model using the following assumptions:


	Three Months Ended March 31,
	2020	2019
Expected term (in years)	6.08	6.08
Volatility	65.2% - 65.6%	69.3% - 69.4%
Risk-free interest rate	0.7% - 1.7%	2.5% - 2.6%
Dividend yield	—	—

Restricted Stock Activity

Aggregated information regarding RSAs and RSUs granted under the 2017 Plan for the three months ended March 31, 2020 is summarized below:


	Share Awards & Units	Weighted-Average Fair Value at Date of Grant per Share
Unvested at December 31, 2019	882,636	$	18.67
Granted	868,500	24.50
Vested and released	(91,839)	18.60
Forfeited	(21,313)	18.34
Unvested at March 31, 2020	1,637,984	$	21.75
Expected to vest - March 31, 2020	1,637,984	$	21.75

Summary of Stock-Based Compensation Expense

The Company’s results of operations include expenses relating to stock-based compensation as follows (in thousands):


	Three Months Ended March 31,
	2020		2019
Research and development	$	6,054	$	3,982
General and administrative	4,731		2,892
Total	$	10,785	$	6,874

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Schedule of Dilutive Securities Not Included in Diluted Per Share Calculations

Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:


	Three Months Ended March 31,
	2020	2019
Options issued and outstanding and ESPP shares issuable	14,530,378	12,202,568
Restricted shares subject to future vesting	1,637,984	524,359
Early exercised common stock subject to future vesting	—	88,550
Total	16,168,362	12,815,477

Significant Accounting Policies - Narrative (Details)	3 Months Ended
Significant Accounting Policies - Narrative (Details)	Mar. 31, 2020 Segment
Accounting Policies [Abstract]
Number of operating segments	1

Fair Value Measurements - Schedule of Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	$ 389,397	$ 375,793
Foreign currency derivative contracts		85
Total	569,549	446,030
Liability - foreign currency derivative contracts	141	8
Total	141	8
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	92,160	54,163
U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	84,996	15,989
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,996
Short-term marketable securities: \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	273,680	250,070
Short-term marketable securities: \| U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value		2,000
Short-term marketable securities: \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	61,766	53,479
Short-term marketable securities: \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	44,267	30,358
Long-term marketable securities: \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	2,565	13,869
Long-term marketable securities: \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	7,119	26,017
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency derivative contracts		0
Total	453,401	334,091
Liability - foreign currency derivative contracts	0	0
Total	0	0
Level 1 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	92,160	54,163
Level 1 \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	84,996	15,989
Level 1 \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0
Level 1 \| Short-term marketable securities: \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	273,680	250,070
Level 1 \| Short-term marketable securities: \| U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value		0
Level 1 \| Short-term marketable securities: \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 1 \| Short-term marketable securities: \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 1 \| Long-term marketable securities: \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	2,565	13,869
Level 1 \| Long-term marketable securities: \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency derivative contracts		85
Total	116,148	111,939
Liability - foreign currency derivative contracts	141	8
Total	141	8
Level 2 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 2 \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 2 \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,996
Level 2 \| Short-term marketable securities: \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 2 \| Short-term marketable securities: \| U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value		2,000
Level 2 \| Short-term marketable securities: \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	61,766	53,479
Level 2 \| Short-term marketable securities: \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	44,267	30,358
Level 2 \| Long-term marketable securities: \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 2 \| Long-term marketable securities: \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	7,119	26,017
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency derivative contracts		0
Total	0	0
Liability - foreign currency derivative contracts	0	0
Total	0	0
Level 3 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 3 \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 3 \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0
Level 3 \| Short-term marketable securities: \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 3 \| Short-term marketable securities: \| U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value		0
Level 3 \| Short-term marketable securities: \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 3 \| Short-term marketable securities: \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 3 \| Long-term marketable securities: \| U.S. government treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	0	0
Level 3 \| Long-term marketable securities: \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate Fair Value	$ 0	$ 0

Cash and Marketable Securities - Schedule of Restricted Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 207,537	$ 79,449	$ 39,661	$ 77,123
Restricted cash included within other non-current assets	1,500	1,500	1,500	1,500
Total cash, cash equivalents, and restricted cash	$ 209,037	$ 80,949	$ 41,161	$ 78,623

Cash and Marketable Securities - Summary of Available for Sale Securities (Details) $ in Thousands	Mar. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 388,154	$ 375,094
Unrealized Holding Gains	1,470	729
Unrealized Holding Losses	(227)	(30)
Aggregate Fair Value	389,397	375,793
Short-term marketable securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	378,476	335,231
Unrealized Holding Gains	1,430	689
Unrealized Holding Losses	(193)	(13)
Aggregate Fair Value	379,713	335,907
Short-term marketable securities: \| U.S. government treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	272,289	249,478
Unrealized Holding Gains	1,391	594
Unrealized Holding Losses	0	(2)
Aggregate Fair Value	273,680	$ 250,070
Number of securities held in unrealized holding loss position \| security		2
Aggregate Fair Value, unrealized holding loss position		$ 9,300
Short-term marketable securities: \| Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	61,920	53,396
Unrealized Holding Gains	39	94
Unrealized Holding Losses	(193)	(11)
Aggregate Fair Value	$ 61,766	$ 53,479
Number of securities held in unrealized holding loss position \| security	10	4
Aggregate Fair Value, unrealized holding loss position	$ 35,700	$ 25,900
Short-term marketable securities: \| U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,999
Unrealized Holding Gains		1
Unrealized Holding Losses		0
Aggregate Fair Value		2,000
Short-term marketable securities: \| Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44,267	30,358
Unrealized Holding Gains	0	0
Unrealized Holding Losses	0	0
Aggregate Fair Value	44,267	30,358
Long-term marketable securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,678	39,863
Unrealized Holding Gains	40	40
Unrealized Holding Losses	(34)	(17)
Aggregate Fair Value	9,684	39,886
Long-term marketable securities: \| U.S. government treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,525	13,865
Unrealized Holding Gains	40	6
Unrealized Holding Losses	0	(2)
Aggregate Fair Value	2,565	$ 13,869
Number of securities held in unrealized holding loss position \| security		1
Aggregate Fair Value, unrealized holding loss position		$ 10,100
Long-term marketable securities: \| Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,153	25,998
Unrealized Holding Gains	0	34
Unrealized Holding Losses	(34)	(15)
Aggregate Fair Value	$ 7,119	$ 26,017
Number of securities held in unrealized holding loss position \| security	1	3
Aggregate Fair Value, unrealized holding loss position	$ 7,100	$ 17,200

Cash and Marketable Securities - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Cash and Cash Equivalents [Abstract]
Allowance for credit losses	$ 0		$ 0
Tax benefit	135,000	$ 0
Tax charge in other comprehensive income	$ 100,000	$ 0
Effective maturity (less than)	2 years

Derivative Financial Instruments - Summary of Forward Foreign Currency Exchange Contracts Outstanding (Details) - Designated as Hedging Instrument € in Thousands, £ in Thousands, SFr in Thousands	Mar. 31, 2020 EUR (€) derivative_instrument	Mar. 31, 2020 GBP (£) derivative_instrument	Mar. 31, 2020 CHF (SFr) derivative_instrument	Dec. 31, 2019 EUR (€) derivative_instrument	Dec. 31, 2019 GBP (£) derivative_instrument	Dec. 31, 2019 CHF (SFr) derivative_instrument
Euros
Derivative [Line Items]
Number of Contracts	26	26	26	23	23	23
Aggregate Notional Amount in Foreign Currency \| €	€ 2,746			€ 1,500
British Pounds
Derivative [Line Items]
Number of Contracts	17	17	17	15	15	15
Aggregate Notional Amount in Foreign Currency \| £		£ 2,482			£ 2,285
Swiss Francs
Derivative [Line Items]
Number of Contracts	5	5	5	10	10	10
Aggregate Notional Amount in Foreign Currency \| SFr			SFr 34			SFr 129
Foreign Exchange Contracts
Derivative [Line Items]
Number of Contracts	48	48	48	48	48	48

Acquisition - Narrative (Details) - USD ($)			1 Months Ended	3 Months Ended		22 Months Ended	44 Months Ended
Acquisition - Narrative (Details) - USD ($)	May 30, 2018	Aug. 24, 2016	Aug. 31, 2016	Mar. 31, 2020	Mar. 31, 2019	May 31, 2018	Mar. 31, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development				$ 51,016,000	$ 37,403,000
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount paid						$ 11,500,000
Upfront option fee			$ 500,000
Contingent consideration recognized	$ 0			0	0
Research and development				$ 300,000	$ 200,000		$ 19,800,000
Maximum development plan period for research costs		24 months
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma \| Exercise of buy-out option
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial option exercise payments		$ 17,800,000
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma \| Exercise of buy-out option \| Preclinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	27,000,000.0
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma \| Exercise of buy-out option \| Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	50,000,000.0
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma \| Exercise of buy-out option \| Regulatory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	120,000,000.0
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma \| Exercise of buy-out option \| Commercial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	250,000,000.0
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma \| Exercise of buy-out option \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	$ 447,000,000.0

Collaboration Agreements - Sanofi (Details) $ in Thousands	1 Months Ended		3 Months Ended		18 Months Ended
Collaboration Agreements - Sanofi (Details) $ in Thousands	Jul. 31, 2019 USD ($)	Nov. 30, 2018 USD ($) indication	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of indications \| indication		3
Sales			$ 3,552	$ 4,111
Sanofi \| Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment		$ 125,000
Milestone payments upon achievement of certain clinical, regulatory and sales milestone events		$ 1,100,000
Funded percentage		70.00%
Increase in transaction price					$ 23,300
Receivable			500		500	$ 1,200
Sanofi \| Collaborative Arrangement \| CNS Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Clinical milestone payment		$ 215,000
Regulatory milestone payment		385,000
Sanofi \| Collaborative Arrangement \| Peripheral Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Clinical milestone payment		120,000
Regulatory milestone payment		175,000
Commercial milestone payments		$ 200,000
Sanofi \| Collaborative Arrangement \| Retained Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Increase in transaction price			$ 500	$ 3,400	13,300
Sanofi \| Collaborative Arrangement \| Milestone Triggered
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales	$ 10,000				10,000
Sanofi \| Collaborative Arrangement \| Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales					$ 0
Denali \| Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Funded percentage		30.00%

Collaboration Agreements - Sanofi Performance Obligation (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Alzheimer's Disease Services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation	$ 3.4	$ 3.5

Collaboration Agreements - Takeda (Details) $ / shares in Units, $ in Thousands		3 Months Ended		12 Months Ended	27 Months Ended
	Feb. 23, 2018 USD ($) program targets $ / shares shares	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales		$ 3,552	$ 4,111
Collaborative Arrangement \| Takeda Pharmaceutical Company Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment	$ 40,000
Number of programs \| program	3
Preclinical milestone payment received	$ 5,000
Number of targets \| targets	3
Target option period	5 years
Option fee	$ 5,000
Variable consideration relating to future milestones	26,000
Remaining preclinical milestones, cost and profit sharing income, and the development and commercial milestones	$ 44,000
Number of performance obligations \| program	3
Contract liability		56,000		$ 59,000	$ 56,000
Preclinical milestone payment earned not yet received		0		0	0
Revenue recognized		$ 3,300		$ 2,400
Sales					15,000
Collaborative Arrangement \| Takeda Pharmaceutical Company Limited \| Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales					$ 0
Collaborative Arrangement \| Share Purchase Agreement \| Takeda Pharmaceutical Company Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of common stock (in shares) \| shares	4,214,559
Purchase price	$ 110,000
Fair market value of common stock	$ 94,400
Closing stock price (usd per share) \| $ / shares	$ 22.40
Premium on sale of common stock	$ 15,600
Collaborative Arrangement \| Maximum \| Takeda Pharmaceutical Company Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Preclinical milestone payments per program	25,000
Total aggregate payments due upon achievement of certain preclinical milestone events	75,000
Aggregated option exercise fee	15,000
Total aggregate payments due upon achievement of certain clinical and regulatory milestone events	407,500
Regulatory milestone payment	300,000
Milestone payments per biologic product upon achievement of a certain sales-based milestone	75,000
Milestone payments upon achievement of biologic product from each program	$ 225,000

Collaboration Agreements - Summary of Collaboration Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	$ 3,552	$ 4,111
Collaborative revenue, excluding revenue from contract with customer	52	94
Collaborative Revenue	3,604	4,205
Takeda Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	3,018	682
Sanofi Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative Revenue	586	3,523
Sanofi Collaboration Agreement \| Alzheimer's Disease Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, excluding revenue from contract with customer	52	94
Sanofi Collaboration Agreement \| Retained Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	$ 534	$ 3,429

License Agreements - Narrative (Details) - Genentech Inc - USD ($)	1 Months Ended	3 Months Ended		46 Months Ended
	Jun. 30, 2016	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020
License Agreement \| Research and Development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fee paid		$ 0	$ 0	$ 12,500,000
Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	$ 37,500,000
Regulatory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	102,500,000
Commercial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	175,000,000.0
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of specified clinical and regulatory milestones	$ 315,000,000.0

Commitments and Contingencies - Narrative (Details)		3 Months Ended
Commitments and Contingencies - Narrative (Details)	May 02, 2018 USD ($) ft²	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Oct. 31, 2018 ft²
Loss Contingencies [Line Items]
Discount rate (as a percentage)		9.00%
Operating lease costs		$ 2,600,000	$ 2,300,000
Weighted average remaining lease term		9 years 1 month 6 days
Weighted-average discount rate (as a percentage)		9.00%
Cash paid for lease liabilities		$ 2,200,000	700,000
Sublease income		900,000	0
DMSA
Loss Contingencies [Line Items]
Purchase order executed		14,600,000		$ 21,200,000
Non-refundable purchase commitments		7,600,000		$ 11,200,000
Costs incurred		1,000,000.0	3,600,000
Payments for development and manufacturing services		$ 3,200,000	$ 2,600,000
Headquarters Lease
Loss Contingencies [Line Items]
Area under lease \| ft²	148,020
Lease period	10 years
Lease renewal option term	10 years
Headquarters Lease \| Landlord Funded Tenant Improvements
Loss Contingencies [Line Items]
Tenant improvement allowance repayable in rent	$ 4,400,000
New Premises Sublease Agreement
Loss Contingencies [Line Items]
Rentable square feet \| ft²					36,835
Sublease term					5 years
Minimum \| Headquarters Lease
Loss Contingencies [Line Items]
Lease renewal notice period	9 months
Maximum
Loss Contingencies [Line Items]
Leasehold improvements	$ 25,900,000
Maximum \| Headquarters Lease
Loss Contingencies [Line Items]
Lease renewal notice period	12 months

Commitments and Contingencies - Summary of Company's Future Minimum Lease Commitments (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Operating Lease Liabilities, Payments Due [Abstract]
2020 (nine months)	$ 7,572
2021	10,391
2022	10,731
2023	11,083
2024	11,447
Thereafter	54,074
Total undiscounted lease payments	105,298
Present value adjustment	(33,384)
Net operating lease liabilities	$ 71,914

Commitments and Contingencies - Summary of Company's Future Minimum Lease Receivables (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2020 (nine months)	$ 2,146
2021	2,925
2022	3,009
2023	3,096
2024	876
Thereafter	0
Total undiscounted sublease receipts	$ 12,052

Stock-Based Awards - Narrative (Details) - USD ($)	1 Months Ended				3 Months Ended
Stock-Based Awards - Narrative (Details) - USD ($)	Dec. 31, 2017	Nov. 30, 2015	Aug. 31, 2015	May 31, 2015	Mar. 31, 2020	Mar. 31, 2019	Jan. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of options exercised					$ 3,700,000	$ 3,300,000
Weighted average grant date fair value of options vested (usd per share)					$ 11.23	$ 11.82
Estimated fair value of option (usd per share)					$ 14.73	11.60
Dividends paid					$ 0
Dividend yield					0.00%
Number of options, granted (in shares)					2,998,584
Exercise price (usd per share)					$ 7.57
Performance and Market Contingent Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options, granted (in shares)		100,000	1,600,000
Exercise price (usd per share)		$ 0.68	$ 0.68
Vesting trigger, number of consecutive trading days					90 days
Vesting trigger, number of days after IPO					180 days
Share based compensation cost not recognized					$ 200,000
Period of recognition					6 months
Performance and Market Contingent Stock Options \| General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance and market-contingent awards expense					$ 100,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of units expected to vest					$ 28,700,000
Weighted-average fair value at date of grant per share, granted (usd per share)					$ 24.50	$ 18.27
Fair value of units vested					$ 2,100,000	$ 7,400,000
2017 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	1,000,000.0
Number of additional shares allowable under the plan (in shares)	2,000,000.0						1,000,000.0
Percent of outstanding shares	1.00%
Common stock purchase discounted rate for employees	85.00%
Maximum employee contribution to ESPP, percent of base compensation	15.00%
Stock issued during period (in shares)					0	0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield					0.00%	0.00%
Unamortized stock- based compensation expense related to unvested stock options					$ 129,500,000
Expected weighted average period					3 years 2 months 12 days
2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	6,400,000
Number of shares available for grant (in shares)					4,500,000			3,400,000
Number of additional shares allowable under the plan (in shares)	10,000,000.0						4,800,000
Percent of outstanding shares	5.00%
2015 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)				8,300,000
Number of shares available for grant (in shares)					0
Shares Transferred As Available For Issuance From 2015 Plan to 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)	200,000
Maximum \| 2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period	10 years
Maximum \| 2015 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period				10 years
Minimum \| 2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of option price of estimated fair value on grant date	100.00%
Award vesting period	4 years
Minimum \| 2015 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of option price of estimated fair value on grant date				100.00%
Award vesting period				4 years

Stock-Based Awards - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Number of Options
Number of options, beginning balance (in shares)	11,640,734
Number of options, granted (in shares)	2,998,584
Number of options, exercised (in shares)	(259,569)
Number of options, forfeited (in shares)	(130,071)
Number of options, ending balance (in shares)	14,249,678	11,640,734
Number of options, vested and expected to vest (in shares)	12,504,946
Number of options, exercisable (in shares)	4,729,113
Weighted- Average Exercise Price
Weighted average exercise price, beginning balance (usd per share)	$ 12.96
Weighted average exercise price, granted (usd per share)	24.63
Weighted average exercise price, exercised (usd per share)	7.57
Weighted average exercise price, forfeited (usd per share)	18.02
Weighted average exercise price, ending balance (usd per share)	15.47	$ 12.96
Weighted average exercise price, vested and expected to vest (usd per share)	17.53
Weighted average exercise price, exercisable (usd per share)	$ 12.63
Stock Option Activity, Additional Disclosures
Weighted average remaining contractual life	8 years 10 days	7 years 9 months 14 days
Weighted average remaining contractual life, vested and expected to vest	8 years 4 months 24 days
Weighted average remaining contractual life, exercisable	7 years 5 months 1 day
Aggregate intrinsic value, ending balance	$ 64,492
Aggregate intrinsic value, vested and expected to vest	35,128
Aggregate intrinsic value	$ 29,163

Stock-Based Awards - Summary of Assumptions Used for Estimating the Fair Value of Stock Options Granted (Details)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days
Volatility, minimum	65.20%	69.30%
Volatility, maximum	65.60%	69.40%
Risk-free interest rate, minimum	0.70%	2.50%
Risk-free interest rate, maximum	1.70%	2.60%
Dividend yield	0.00%	0.00%

Stock-Based Awards - Summary of Restricted Stock Activity (Details) - Restricted Stock - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share Awards & Units
Shares, unvested, beginning balance (in shares)	882,636
Shares, granted (in shares)	868,500
Shares, vested and released (in shares)	(91,839)
Shares, forfeited (in shares)	(21,313)
Shares, unvested, ending balance (in shares)	1,637,984
Shares, expected to vest (in shares)	1,637,984
Weighted-Average Fair Value at Date of Grant per Share
Weighted-average fair value at date of grant per share, unvested, beginning balance (usd per share)	$ 18.67
Weighted-average fair value at date of grant per share, granted (usd per share)	24.50	$ 18.27
Weighted-average fair value at date of grant per share, vested and released (usd per share)	18.60
Weighted-average fair value at date of grant per share, forfeited (usd per share)	18.34
Weighted-average fair value at date of grant per share, unvested, ending balance (usd per share)	21.75
Weighted-average fair value at date of grant per share, expected to vest (usd per share)	$ 21.75

Stock-Based Awards - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total	$ 10,785	$ 6,874
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total	6,054	3,982
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total	$ 4,731	$ 2,892

Net Loss Per Share - Schedule of Dilutive Securities Not Included in Diluted Per Share Calculations (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	16,168,362	12,815,477
Options issued and outstanding and ESPP shares issuable
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	14,530,378	12,202,568
Restricted shares subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	1,637,984	524,359
Early exercised common stock subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	0	88,550