Alector (ALEC) 10-Q 10 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Nov. 01, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	ALEC
Entity File Number	001-38792
Entity Tax Identification Number	82-2933343
Entity Address, Address Line One	131 Oyster Point Blvd
Entity Address, Address Line Two	Suite 600
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	415
Local Phone Number	231-5660
Document Transition Report	false
Document Quarterly Report	true
Entity Registrant Name	Alector, Inc.
Entity Central Index Key	0001653087
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		79,242,709
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 84,979	$ 89,641
Marketable securities	376,735	263,432
Prepaid expenses and other current assets	8,298	4,364
Total current assets	470,012	357,437
Property and equipment, net	30,583	33,852
Operating lease right-of-use assets	27,304	28,476
Restricted cash	1,472	1,472
Other assets	2,217	676
Total Assets	531,588	421,913
Current liabilities:
Accounts payable	1,370	278
Accrued clinical supply costs	9,320	6,706
Accrued liabilities	27,065	18,256
Deferred revenue, current portion	26,596	30,165
Operating lease liabilities, current portion	6,736	6,565
Total current liabilities	71,087	61,970
Deferred revenue, long-term portion	110,560	123,236
Operating lease liabilities, long-term portion	39,257	41,471
Other long-term liabilities	493	493
Total liabilities	221,397	227,170
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized as of September 30, 2020 and December 31, 2019	8	7
Additional paid-in capital	666,958	414,414
Accumulated other comprehensive income	1,094	142
Accumulated deficit	(357,869)	(219,820)
Total stockholders' equity	310,191	194,743
Total liabilities and stockholders’ equity	$ 531,588	$ 421,913

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Total revenue	$ 5,904	$ 2,696	$ 16,245	$ 15,218
Type of Revenue [Extensible List]	alec:CollaborationRevenueMember	alec:CollaborationRevenueMember	alec:CollaborationRevenueMember	alec:CollaborationRevenueMember
Operating expenses:
Research and development	$ 43,819	$ 28,519	$ 112,486	$ 74,766
General and administrative	15,834	8,326	46,175	22,514
Total operating expenses	59,653	36,845	158,661	97,280
Loss from operations	(53,749)	(34,149)	(142,416)	(82,062)
Other income, net	1,045	2,411	4,367	7,204
Net loss	(52,704)	(31,738)	(138,049)	(74,858)
Unrealized gain (loss) on marketable securities	(752)	(215)	952	268
Comprehensive loss	$ (53,456)	$ (31,953)	$ (137,097)	$ (74,590)
Net loss per share, basic and diluted	$ (0.67)	$ (0.47)	$ (1.78)	$ (1.25)
Shares used in computing net loss per share, basic and diluted	78,771,930	67,572,452	77,340,896	59,663,773

Condensed Consolidated Statem_2

Condensed Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2018	$ (97,398)		$ 1	$ 17,078	$ (42)	$ (114,435)
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2018		45,374,836
Convertible preferred stock, beginning balance at Dec. 31, 2018		$ 210,520
Beginning balance (in shares) at Dec. 31, 2018			13,764,829
Issuance of common stock upon initial public offering, net of issuance costs	168,223		$ 1	168,222
Issuance of common stock upon initial public offering, net of issuance costs (in shares)			9,739,541
Conversion of convertible preferred stock into common stock	210,521	$ (210,520)	$ 5	210,516
Conversion of convertible preferred stock into common stock (in shares)		(45,374,836)	45,374,836
Exercise of stock options	5			5
Exercise of stock options (in shares)			625
Forfeiture of restricted common stock (in shares)			(8,039)
Stock-based compensation	3,245			3,245
Unrealized gain (loss) on marketable securities	150				150
Net loss	(18,560)					(18,560)
Ending Balance at Mar. 31, 2019	266,186		$ 7	399,066	108	(132,995)
Ending balance (in shares) at Mar. 31, 2019			68,871,792
Beginning Balance at Dec. 31, 2018	(97,398)		$ 1	17,078	(42)	(114,435)
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2018		45,374,836
Convertible preferred stock, beginning balance at Dec. 31, 2018		$ 210,520
Beginning balance (in shares) at Dec. 31, 2018			13,764,829
Net loss	(74,858)
Ending Balance at Sep. 30, 2019	218,587		$ 7	407,647	226	(189,293)
Ending balance (in shares) at Sep. 30, 2019			68,922,249
Beginning Balance at Mar. 31, 2019	266,186		$ 7	399,066	108	(132,995)
Beginning balance (in shares) at Mar. 31, 2019			68,871,792
Exercise of stock options	63			63
Exercise of stock options (in shares)			8,999
Forfeiture of restricted common stock (in shares)			(48,934)
Stock-based compensation	3,694			3,694
Unrealized gain (loss) on marketable securities	333				333
Net loss	(24,560)					(24,560)
Ending Balance at Jun. 30, 2019	245,716		$ 7	402,823	441	(157,555)
Ending balance (in shares) at Jun. 30, 2019			68,831,857
Exercise of stock options	720			720
Exercise of stock options (in shares)			90,392
Stock-based compensation	4,104			4,104
Unrealized gain (loss) on marketable securities	(215)				(215)
Net loss	(31,738)					(31,738)
Ending Balance at Sep. 30, 2019	218,587		$ 7	407,647	226	(189,293)
Ending balance (in shares) at Sep. 30, 2019			68,922,249
Beginning Balance at Dec. 31, 2019	194,743		$ 7	414,414	142	(219,820)
Beginning balance (in shares) at Dec. 31, 2019			69,052,873
Issuance of common stock upon initial public offering, net of issuance costs	224,511		$ 1	224,510
Issuance of common stock upon initial public offering, net of issuance costs (in shares)			9,602,500
Exercise of stock options	3,217			3,217
Exercise of stock options (in shares)			361,096
Stock-based compensation	6,642			6,642
Unrealized gain (loss) on marketable securities	2,640				2,640
Net loss	(40,019)					(40,019)
Ending Balance at Mar. 31, 2020	391,734		$ 8	648,783	2,782	(259,839)
Ending balance (in shares) at Mar. 31, 2020			79,016,469
Beginning Balance at Dec. 31, 2019	194,743		$ 7	414,414	142	(219,820)
Beginning balance (in shares) at Dec. 31, 2019			69,052,873
Net loss	(138,049)
Ending Balance at Sep. 30, 2020	310,191		$ 8	666,958	1,094	(357,869)
Ending balance (in shares) at Sep. 30, 2020			79,284,181
Beginning Balance at Mar. 31, 2020	391,734		$ 8	648,783	2,782	(259,839)
Beginning balance (in shares) at Mar. 31, 2020			79,016,469
Exercise of stock options	2,196			2,196
Exercise of stock options (in shares)			190,709
Purchase of common stock under employee stock option	715			715
Purchase of common stock under employee stock option (in shares)			45,217
Stock-based compensation	6,948			6,948
Unrealized gain (loss) on marketable securities	(936)				(936)
Net loss	(45,326)					(45,326)
Ending Balance at Jun. 30, 2020	355,331		$ 8	658,642	1,846	(305,165)
Ending balance (in shares) at Jun. 30, 2020			79,252,395
Exercise of stock options	286			286
Exercise of stock options (in shares)			31,786
Stock-based compensation	8,030			8,030
Unrealized gain (loss) on marketable securities	(752)				(752)
Net loss	(52,704)					(52,704)
Ending Balance at Sep. 30, 2020	$ 310,191		$ 8	$ 666,958	$ 1,094	$ (357,869)
Ending balance (in shares) at Sep. 30, 2020			79,284,181

Condensed Consolidated Statem_3

Condensed Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement Of Stockholders Equity [Abstract]
Issuance cost of common stock	$ 1,148	$ 3,874

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (138,049)	$ (74,858)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	4,367	2,397
Stock-based compensation	21,620	11,043
Amortization of premiums and accretion of discounts on marketable securities	8	(4,027)
Amortization of right-of-use assets	934	1,510
Impairment loss on right-of-use asset	238	1,158
Loss from disposal of property and equipment, net	12	39
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,934)	(1,269)
Other assets	(2,098)	(72)
Accounts payable	1,087	132
Accrued liabilities and accrued clinical supply costs	15,027	7,467
Deferred revenue	(16,245)	(15,218)
Deferred rent		(44)
Lease liabilities	(2,043)	948
Other long-term liabilities		313
Net cash used in operating activities	(119,076)	(70,481)
Cash flows from investing activities:
Purchase of property and equipment	(4,244)	(13,692)
Purchase of marketable securities	(414,949)	(411,239)
Maturities of marketable securities	302,590	346,000
Net cash used in investing activities	(116,603)	(78,931)
Cash flows from financing activities:
Proceeds from issuance of common stock upon initial public offering, net of issuance costs		170,128
Proceeds from issuance of common stock upon follow-on public offering, net of issuance costs	224,603
Proceeds from the exercise of options to purchase common stock	5,699	788
Purchase of common stock under employee stock purchase plan	715
Net cash provided by financing activities	231,017	170,916
Net increase (decrease) in cash, cash equivalents, and restricted cash	(4,662)	21,504
Cash, cash equivalents, and restricted cash at beginning of period	91,113	66,942
Cash, cash equivalents, and restricted cash at end of period	86,451	88,446
Non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	$ 337	3,675
Tenant improvements paid by landlord		$ 8,286

The Company and Liquidity

The Company and Liquidity	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company and Liquidity	1. Alector, Inc. (Alector or the Company) is a Delaware corporation headquartered in South San Francisco, California. Alector is a clinical stage biopharmaceutical company pioneering immuno-neurology, a novel therapeutic approach for the treatment of neurodegeneration. Initial Public and Follow-on Offerings On February 7, 2019, the Company completed an initial public offering (IPO) through issuing and selling 9,739,541 shares of common stock at a public offering price of $19.00 per share, including 489,541 shares sold pursuant to the underwriters’ partial exercise of their option to purchase additional shares, resulting in aggregate net proceeds of $168.2 million, after deducting underwriting discounts and commissions and offering costs. Upon the closing of the IPO, all of the outstanding shares of convertible preferred stock automatically converted into 45,374,836 shares of common stock. Subsequent to the closing of the IPO, there were no shares of convertible preferred stock outstanding. On January 30, 2020, the Company completed a follow-on offering through issuing and selling 9,602,500 shares of common stock at a public offering price of $25.00 per share, including 1,252,500 shares sold pursuant to the underwriters’ full exercise of their option to purchase additional shares, resulting in aggregate net proceeds of $224.5 million, after deducting underwriting discounts and commissions and offering costs.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Basis of Presentation The condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States (GAAP) as defined by the Financial Accounting Standards Board (FASB). In the opinion of management, these unaudited condensed consolidated financial statements include all normal, recurring adjustments that are necessary to present fairly the results of the interim periods presented. The condensed consolidated financial statements include the accounts of Alector, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on March 24, 2020. Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expense during the reporting period. The Company evaluates its estimates, including those related to revenue recognition, manufacturing accruals, clinical accruals, fair value of assets and liabilities, income taxes uncertainties, stock-based compensation, and related assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates . Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, and short-term marketable securities. Cash and cash equivalents are deposited in checking and sweep accounts at a financial institution. Such deposits may, at times, exceed federally insured limits. Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash and cash equivalents. Cash equivalents, which consist of amounts invested in money market funds, are stated at fair value. There are no significant unrealized gains or losses on the money market funds for the periods presented. Restricted cash as of September 30, 2020 relates to a letter of credit established for a lease entered into in June 2018. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same amounts shown in the condensed consolidated statements of cash flows: Nine Months Ended September 30, 2020 2019 (In thousands) Cash and cash equivalents $ 84,979 $ 86,974 Restricted cash 1,472 1,472 Total cash, cash equivalents, and restricted cash $ 86,451 $ 88,446 Fair Value of Financial Instruments The Company’s financial instruments include cash and cash equivalents, marketable securities, accounts payable, and accrued liabilities. The Company’s financial instruments approximate fair value due to their relatively short maturities. The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines the fair value of its financial instruments based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels: Level 1 – Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 – Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 – Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Revenue Recognition The Company entered into an agreement in October 2017 with AbbVie Biotechnology, Ltd. (AbbVie) to co-develop antibodies to two program targets in preclinical development (AbbVie Agreement). Under the terms of the AbbVie Agreement, AbbVie made $205.0 million in upfront payments, of which $5.0 million and $200.0 million was received by the Company in October 2017 and January 2018, respectively. The Company will perform research and development services for the antibodies to the two programs through the end of Phase 2 clinical trials which the Company expects to conduct through 2023. AbbVie will then have the exclusive right to exercise an option to enter into a license and collaboration agreement with the Company for one or both of the programs for $250.0 million each. If AbbVie exercises its option for the programs, AbbVie will take over the development of the product candidates for such program and costs will be split between the parties. The Company will also share in profits and losses upon commercialization of any products from such program. However, following AbbVie’s exercise of its option for a program, the Company may opt out of sharing in development costs and profits or losses for that program and instead receive tiered royalties. Additionally, under the terms of the AbbVie Agreement, the Company will be eligible to earn up to an additional $242.8 million in milestone payments per program related to the initiation of certain clinical studies and regulatory approval for up to three indications per program. The Company assessed its collaboration agreement with AbbVie in the context of the delivery of the research and development services. The Company recognizes collaboration revenue by measuring the progress toward complete satisfaction of the performance obligation using an input measure. In order to recognize revenue over the research and development period, the Company measures actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligation. Revenues are recognized as the program costs are incurred. The Company re-evaluates the estimate of expected costs to satisfy the performance obligation each reporting period and make adjustments for any significant changes. Clinical trials are expensive and can take many years to complete, and the outcome is inherently uncertain. Changes in the Company’s forecasted costs are likely to occur over time based upon changes in clinical trial procedures set forth in protocols, changes in estimates of manufacturing costs, or feedback from regulators on the design or operation of clinical trials. The Company has had changes to the overall expected costs to satisfy the performance obligations from period to period. For the three months ended September 30, 2020, the Company had a 2.3% increase in the forecast of the total expected costs. For the three months ended September 30, 2020, the increase in the overall expected costs to satisfy the performance obligation resulted in an approximately $1.7 million reduction in revenue compared to if the expected costs had remained the same, as a result of the cumulative catch up for the change in estimate. Collaboration revenue under the Company’s collaboration agreement with AbbVie during the three and nine months ended September 30, 2020 was $5.9 million and $16.2 million, respectively, the entire amount of which was included in deferred revenue at the beginning of the period. The Company recorded deferred revenue of $137.2 million as of September 30, 2020. The deferred revenue is expected to be recognized over the research and development period of the programs through the completion of Phase 2 clinical trials. The Company entered into an agreement in March 2020 with Innovent Biologics (Innovent) to license, develop, and commercialize AL008 in China (Innovent Agreement). AL008 is the Company’s novel antibody targeting the CD47-SIRP-alpha pathway, a potent survival pathway co-opted by tumors to evade the innate immune system. Under the terms of the Innovent Agreement, Innovent may pay the Company up to $11.5 million in development milestones, $112.5 million in sales milestones, and future royalties for any sales. The Company retains the rights to develop and commercialize AL008 outside of China. The Company has determined there is one performance obligation for the delivery of the license and will recognize revenue when it is probable that there will not be significant reversal of cumulative revenue. Development and sales milestones under the Innovent Agreement have not been included in the transaction price, as all these amounts were fully constrained as of September 30, 2020. As of September 30, 2020, no revenue has been recognized or payments received under the Innovent Agreement. Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ equity that are the result of transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss was net unrealized gain (loss) on marketable securities. Recently Adopted Accounting Pronouncements Effective January 1, 2020, the Company adopted Accounting Standards Update (ASU) No. 2016-13, Financial Instruments—Credit Losses (Topic 326) In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740) Simplifying the Accounting for Income Taxes.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following tables summarize the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy: September 30, 2020 Fair Value Hierarchy Amortized Cost Unrealized Gains Unrealized Losses Fair Market Value (In thousands) Money market funds Level 1 $ 65,472 $ — $ — $ 65,472 U.S. government treasury securities Level 1 363,248 1,080 (7 ) 364,321 Commercial paper Level 2 4,984 — — 4,984 Corporate bonds Level 2 10,010 21 — 10,031 Total cash equivalents and marketable securities $ 443,714 $ 1,101 $ (7 ) $ 444,808 December 31, 2019 Fair Value Hierarchy Amortized Cost Unrealized Gains Unrealized Losses Fair Market Value (In thousands) Money market funds Level 1 $ 61,104 $ — $ — $ 61,104 U.S. government treasury securities Level 1 227,446 149 (8 ) 227,587 Commercial paper Level 2 43,735 — — 43,735 Corporate bonds Level 2 10,103 3 (2 ) 10,104 Total cash equivalents and marketable securities $ 342,388 $ 152 $ (10 ) $ 342,530 The Company’s Level 2 securities are valued using third-party pricing sources. The pricing services utilize industry standard valuation models for which all significant inputs are observable. The Company classifies marketable securities available to fund current operations as current assets. As of September 30, 2020, the remaining contractual maturities of $359.3 million of investments were less than one year and $85.5 million of investments were after one year through two years. The Company does not intend to sell the investments that are currently in an unrealized loss position, and it is highly unlikely that the Company will be required to sell the investments before recovery of their amortized cost basis, which may be maturity. As of September 30, 2020, the Company considered any unrealized losses on our marketable securities to be driven by factors other than credit risk.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	4 . The Company recognized stock-based compensation as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 (In thousands) (In thousands) Research and development $ 4,058 $ 1,935 $ 10,631 $ 5,515 General and administrative 3,972 2,169 10,989 5,528 Total stock-based compensation $ 8,030 $ 4,104 $ 21,620 $ 11,043 Restricted Common Stock Activity for the restricted common stock is shown below: Number of Shares Weighted Average Grant Date Fair Value per Share Unvested restricted common stock as of December 31, 2019 994,838 $ 6.95 Vested (579,317 ) 6.95 Unvested restricted common stock as of September 30, 2020 415,521 $ 6.95 As of September 30, 2020, total unrecognized stock-based compensation related to unvested restricted common stock was $2.1 million, which the Company expects to recognize over a remaining weighted-average period of 1.0 years. 2019 Equity Incentive Plan On February 6, 2019, the Company adopted the 2019 Equity Incentive Plan (2019 Plan) under which the Board may issue incentive stock options, nonstatutory stock options, restricted stock, restricted stock units, stock appreciation rights, performance units, and performance shares to the Company’s employees, directors, and consultants. The Company initially reserved for issuance 7,688,156 shares of common stock pursuant to the 2019 Plan. The Company’s 2017 Stock Option and Grant Plan (2017 Plan) was terminated; however, shares subject to awards granted under it will continue to be governed by the 2017 Plan. Shares reserved for issuance but not issued pursuant to, or not subject to, awards granted under the 2017 Plan were added to the available shares in the 2019 Plan. Shares subject to awards granted under the 2017 Plan that are repurchased by, or forfeited to, the Company will also be reserved for issuance under the 2019 Plan. On January 1, 2020, the Company added 3,452,643 shares to the shares reserved for issuance. As of September 30, 2020, the Company had reserved 15,618,644 shares of common stock for issuance under the 2019 Plan, of which 5,585,374 shares were available for issuance. Activity for the options to purchase common stock shown below (in thousands, except share and per share amounts): Number of Options Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (In years) Aggregate Intrinsic Value Outstanding as of December 31, 2019 8,442,824 $ 12.79 Granted 2,536,087 21.42 Exercised (583,591 ) 9.77 Forfeited (362,050 ) 16.53 Outstanding as of September 30, 2020 10,033,270 $ 15.01 8.7 $ 6,402 Exercisable as of September 30, 2020 2,834,348 $ 12.22 8.3 $ 3,017 Vested and expected to vest as of September 30, 2020 10,033,270 $ 15.01 8.7 $ 6,402 The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the fair value of the Company’s common stock for stock options that were in-the-money. As of September 30, 2020, total unrecognized stock-based compensation related to unvested stock options was $73.3 million, which the Company expects to recognize over a remaining weighted-average period of 2.8 years. 2019 Employee Stock Purchase Plan On February 6, 2019, the Company adopted the 2019 Employee Stock Option Plan (2019 ESPP). The 2019 ESPP will enable eligible employees of the Company to purchase shares of common stock at a discount. As of September 30, 2020, the Company has reserved for issuance 1,974,319 shares of common stock pursuant to the 2019 ESPP. Each offering period is approximately six months long. ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of (1) the fair market value per share of the common stock on the first trading day of the offering period or (2) the fair market value of the common stock on the purchase date.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Party Transactions	5 . The Company has a collaboration agreement with Adimab, LLC (Adimab) under which the Company is developing antibodies discovered by Adimab in its AL001 and AL101 product candidates, and the Company is developing antibodies optimized by Adimab in its AL002 and AL003 product candidates (2014 Adimab Agreement). In August 2019, the Company signed a new collaboration agreement with Adimab for research and development of additional antibodies (2019 Adimab Agreement). The Chief Executive Officer of Adimab is a Co-founder and Chairperson of the board of directors of Alector. For the three and nine months ended September 30, 2020, the Company incurred no expenses under the Adimab Agreements. For the three and nine months ended September 30, 2019, the Company incurred expenses of $2.0 million and $2.8 million, respectively. The Company had no accrued liabilities due to Adimab as of September 30, 2020 and December 31, 2019. Under the 2014 Adimab Agreement, the Company will owe up to $3.5 million in milestone payments per program to Adimab for its product candidates. The Company will also owe low- to mid- single-digit royalty payments for commercial sales of such product candidates. Under the 2019 Adimab Agreement, the Company will owe certain milestone payments per program for its product candidates and low single-digit royalty payments for commercial sales of such product candidates. On January 30, 2020, in connection with the Company’s follow-on offering, a member of the Company’s board of directors purchased 20,000 shares of the Company’s common stock at the public offering price of $25.00 per share.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	6 . The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: Three and Nine Months Ended September 30, 2020 2019 Restricted stock subject to future vesting 415,521 1,191,750 Options to purchase common stock 10,033,270 5,918,124 Shares committed under ESPP 25,822 51,667 Total 10,474,613 7,161,541

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	7 . In October 2020, the Company signed a lease agreement to lease approximately 18,700 square feet in Newark, CA that will be used for laboratory and office space. The lease commences on December 1, 2020 and is over a 7-year 2-month term with an option to extend for an additional five years. Fixed rent payments under the initial term of the lease are approximately $7.7 million. The Company will also pay a proportionate share of the facility’s operating expenses.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States (GAAP) as defined by the Financial Accounting Standards Board (FASB). In the opinion of management, these unaudited condensed consolidated financial statements include all normal, recurring adjustments that are necessary to present fairly the results of the interim periods presented. The condensed consolidated financial statements include the accounts of Alector, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on March 24, 2020.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expense during the reporting period. The Company evaluates its estimates, including those related to revenue recognition, manufacturing accruals, clinical accruals, fair value of assets and liabilities, income taxes uncertainties, stock-based compensation, and related assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates .
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, and short-term marketable securities. Cash and cash equivalents are deposited in checking and sweep accounts at a financial institution. Such deposits may, at times, exceed federally insured limits.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash and cash equivalents. Cash equivalents, which consist of amounts invested in money market funds, are stated at fair value. There are no significant unrealized gains or losses on the money market funds for the periods presented. Restricted cash as of September 30, 2020 relates to a letter of credit established for a lease entered into in June 2018. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same amounts shown in the condensed consolidated statements of cash flows: Nine Months Ended September 30, 2020 2019 (In thousands) Cash and cash equivalents $ 84,979 $ 86,974 Restricted cash 1,472 1,472 Total cash, cash equivalents, and restricted cash $ 86,451 $ 88,446
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial instruments include cash and cash equivalents, marketable securities, accounts payable, and accrued liabilities. The Company’s financial instruments approximate fair value due to their relatively short maturities. The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines the fair value of its financial instruments based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels: Level 1 – Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 – Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 – Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.
Revenue Recognition	Revenue Recognition The Company entered into an agreement in October 2017 with AbbVie Biotechnology, Ltd. (AbbVie) to co-develop antibodies to two program targets in preclinical development (AbbVie Agreement). Under the terms of the AbbVie Agreement, AbbVie made $205.0 million in upfront payments, of which $5.0 million and $200.0 million was received by the Company in October 2017 and January 2018, respectively. The Company will perform research and development services for the antibodies to the two programs through the end of Phase 2 clinical trials which the Company expects to conduct through 2023. AbbVie will then have the exclusive right to exercise an option to enter into a license and collaboration agreement with the Company for one or both of the programs for $250.0 million each. If AbbVie exercises its option for the programs, AbbVie will take over the development of the product candidates for such program and costs will be split between the parties. The Company will also share in profits and losses upon commercialization of any products from such program. However, following AbbVie’s exercise of its option for a program, the Company may opt out of sharing in development costs and profits or losses for that program and instead receive tiered royalties. Additionally, under the terms of the AbbVie Agreement, the Company will be eligible to earn up to an additional $242.8 million in milestone payments per program related to the initiation of certain clinical studies and regulatory approval for up to three indications per program. The Company assessed its collaboration agreement with AbbVie in the context of the delivery of the research and development services. The Company recognizes collaboration revenue by measuring the progress toward complete satisfaction of the performance obligation using an input measure. In order to recognize revenue over the research and development period, the Company measures actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligation. Revenues are recognized as the program costs are incurred. The Company re-evaluates the estimate of expected costs to satisfy the performance obligation each reporting period and make adjustments for any significant changes. Clinical trials are expensive and can take many years to complete, and the outcome is inherently uncertain. Changes in the Company’s forecasted costs are likely to occur over time based upon changes in clinical trial procedures set forth in protocols, changes in estimates of manufacturing costs, or feedback from regulators on the design or operation of clinical trials. The Company has had changes to the overall expected costs to satisfy the performance obligations from period to period. For the three months ended September 30, 2020, the Company had a 2.3% increase in the forecast of the total expected costs. For the three months ended September 30, 2020, the increase in the overall expected costs to satisfy the performance obligation resulted in an approximately $1.7 million reduction in revenue compared to if the expected costs had remained the same, as a result of the cumulative catch up for the change in estimate. Collaboration revenue under the Company’s collaboration agreement with AbbVie during the three and nine months ended September 30, 2020 was $5.9 million and $16.2 million, respectively, the entire amount of which was included in deferred revenue at the beginning of the period. The Company recorded deferred revenue of $137.2 million as of September 30, 2020. The deferred revenue is expected to be recognized over the research and development period of the programs through the completion of Phase 2 clinical trials. The Company entered into an agreement in March 2020 with Innovent Biologics (Innovent) to license, develop, and commercialize AL008 in China (Innovent Agreement). AL008 is the Company’s novel antibody targeting the CD47-SIRP-alpha pathway, a potent survival pathway co-opted by tumors to evade the innate immune system. Under the terms of the Innovent Agreement, Innovent may pay the Company up to $11.5 million in development milestones, $112.5 million in sales milestones, and future royalties for any sales. The Company retains the rights to develop and commercialize AL008 outside of China. The Company has determined there is one performance obligation for the delivery of the license and will recognize revenue when it is probable that there will not be significant reversal of cumulative revenue. Development and sales milestones under the Innovent Agreement have not been included in the transaction price, as all these amounts were fully constrained as of September 30, 2020. As of September 30, 2020, no revenue has been recognized or payments received under the Innovent Agreement.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ equity that are the result of transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss was net unrealized gain (loss) on marketable securities.
New Accounting Pronouncements	Recently Adopted Accounting Pronouncements Effective January 1, 2020, the Company adopted Accounting Standards Update (ASU) No. 2016-13, Financial Instruments—Credit Losses (Topic 326) In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740) Simplifying the Accounting for Income Taxes.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same amounts shown in the condensed consolidated statements of cash flows: Nine Months Ended September 30, 2020 2019 (In thousands) Cash and cash equivalents $ 84,979 $ 86,974 Restricted cash 1,472 1,472 Total cash, cash equivalents, and restricted cash $ 86,451 $ 88,446

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on a Recurring Basis	The following tables summarize the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy: September 30, 2020 Fair Value Hierarchy Amortized Cost Unrealized Gains Unrealized Losses Fair Market Value (In thousands) Money market funds Level 1 $ 65,472 $ — $ — $ 65,472 U.S. government treasury securities Level 1 363,248 1,080 (7 ) 364,321 Commercial paper Level 2 4,984 — — 4,984 Corporate bonds Level 2 10,010 21 — 10,031 Total cash equivalents and marketable securities $ 443,714 $ 1,101 $ (7 ) $ 444,808 December 31, 2019 Fair Value Hierarchy Amortized Cost Unrealized Gains Unrealized Losses Fair Market Value (In thousands) Money market funds Level 1 $ 61,104 $ — $ — $ 61,104 U.S. government treasury securities Level 1 227,446 149 (8 ) 227,587 Commercial paper Level 2 43,735 — — 43,735 Corporate bonds Level 2 10,103 3 (2 ) 10,104 Total cash equivalents and marketable securities $ 342,388 $ 152 $ (10 ) $ 342,530

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Recognized Stock-Based Compensation	The Company recognized stock-based compensation as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 (In thousands) (In thousands) Research and development $ 4,058 $ 1,935 $ 10,631 $ 5,515 General and administrative 3,972 2,169 10,989 5,528 Total stock-based compensation $ 8,030 $ 4,104 $ 21,620 $ 11,043
Summary of Restricted Common Stock	Activity for the restricted common stock is shown below: Number of Shares Weighted Average Grant Date Fair Value per Share Unvested restricted common stock as of December 31, 2019 994,838 $ 6.95 Vested (579,317 ) 6.95 Unvested restricted common stock as of September 30, 2020 415,521 $ 6.95
Summary of Options to Purchase Common Stock	Activity for the options to purchase common stock shown below (in thousands, except share and per share amounts): Number of Options Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (In years) Aggregate Intrinsic Value Outstanding as of December 31, 2019 8,442,824 $ 12.79 Granted 2,536,087 21.42 Exercised (583,591 ) 9.77 Forfeited (362,050 ) 16.53 Outstanding as of September 30, 2020 10,033,270 $ 15.01 8.7 $ 6,402 Exercisable as of September 30, 2020 2,834,348 $ 12.22 8.3 $ 3,017 Vested and expected to vest as of September 30, 2020 10,033,270 $ 15.01 8.7 $ 6,402

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: Three and Nine Months Ended September 30, 2020 2019 Restricted stock subject to future vesting 415,521 1,191,750 Options to purchase common stock 10,033,270 5,918,124 Shares committed under ESPP 25,822 51,667 Total 10,474,613 7,161,541

The Company and Liquidity - Add

The Company and Liquidity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 30, 2020	Feb. 07, 2019	Mar. 31, 2020	Mar. 31, 2019
Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings			9,602,500	9,739,541
Initial Public Offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings		9,739,541
Share price		$ 19
Proceeds from issuance of common stock, net of underwriting discounts and commissions and offering expenses		$ 168.2
Convertible preferred stock, shares outstanding		0
Initial Public Offering | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Conversion of convertible preferred stock to common stock		45,374,836
Over-Allotment Option
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings	1,252,500	489,541
Follow-on-offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Public offerings	9,602,500
Share price	$ 25
Proceeds from issuance of common stock, net of underwriting discounts and commissions and offering expenses	$ 224.5

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended	9 Months Ended
	Jan. 31, 2018	Oct. 31, 2017	Sep. 30, 2020	Sep. 30, 2020
Summary Of Significant Accounting Policies [Line Items]
Increase in expected cost percentage			2.30%
Reduced revenue			$ 1,700,000
Available-for-Sale Investments | ASU 2016-13
Summary Of Significant Accounting Policies [Line Items]
Accrued interest receivable			1,200,000	$ 1,200,000
AbbVie Biotechnology Limited
Summary Of Significant Accounting Policies [Line Items]
Upfront payments		$ 205,000,000
Upfront payment received	$ 200,000,000	5,000,000
Exclusive option rights exercised for each program		250,000,000
Collaboration revenue			5,900,000	16,200,000
Deferred revenue			$ 137,200,000	137,200,000
AbbVie Biotechnology Limited | Maximum
Summary Of Significant Accounting Policies [Line Items]
Additional milestone payments per program related to initiation of certain clinical studies and regulatory approval		$ 242,800,000
Innovent
Summary Of Significant Accounting Policies [Line Items]
Collaboration revenue				0
Development milestone				11,500,000
Sales milestone				112,500,000
Money Market Funds
Summary Of Significant Accounting Policies [Line Items]
Unrealized gains or loss on money market funds				$ 0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 84,979	$ 89,641	$ 86,974
Restricted cash	1,472	1,472	1,472
Total cash, cash equivalents, and restricted cash	$ 86,451	$ 91,113	$ 88,446	$ 66,942

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	$ 65,472	$ 61,104
Cash equivalents and marketable securities, Fair Market Value	65,472	61,104
U.S Government Treasury Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	363,248	227,446
Cash equivalents and marketable securities, Unrealized Gains	1,080	149
Cash equivalents and marketable securities, Unrealized Losses	(7)	(8)
Cash equivalents and marketable securities, Fair Market Value	364,321	227,587
Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	4,984	43,735
Cash equivalents and marketable securities, Fair Market Value	4,984	43,735
Corporate Bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	10,010	10,103
Cash equivalents and marketable securities, Unrealized Gains	21	3
Cash equivalents and marketable securities, Unrealized Losses		(2)
Cash equivalents and marketable securities, Fair Market Value	10,031	10,104
Cash Equivalents and Marketable Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents and marketable securities, Amortized Cost	443,714	342,388
Cash equivalents and marketable securities, Unrealized Gains	1,101	152
Cash equivalents and marketable securities, Unrealized Losses	(7)	(10)
Cash equivalents and marketable securities, Fair Market Value	$ 444,808	$ 342,530

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) $ in Millions	Sep. 30, 2020USD ($)
Fair Value Disclosures [Abstract]
Remaining contractual maturities of investments were less than one year	$ 359.3
Remaining contractual maturities of investments were less than one year through two years	$ 85.5

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Recognized Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 8,030	$ 4,104	$ 21,620	$ 11,043
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	4,058	1,935	10,631	5,515
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 3,972	$ 2,169	$ 10,989	$ 5,528

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Restricted Common Stock (Details) - Restricted Common Stock	9 Months Ended
	Sep. 30, 2020$ / sharesshares
Number of Shares
Number of Shares, Unvested, beginning balance | shares	994,838
Number of Shares, Vested | shares	(579,317)
Number of Shares, Unvested, ending balance | shares	415,521
Weighted-average grant-date fair value
Weighted Average Grant Date Fair Value per Share, Unvested, beginning balance | $ / shares	$ 6.95
Weighted Average Grant Date Fair Value per Share, Vested | $ / shares	6.95
Weighted Average Grant Date Fair Value per Share, Unvested, ending balance | $ / shares	$ 6.95

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($) $ in Millions	Feb. 06, 2019	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected weighted average period		2 years 9 months 18 days
Common stock reserved for issuance	7,688,156	15,618,644		3,452,643
Common stock, shares available for issuance			5,585,374
Unrecognized stock-based compensation		$ 73.3
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance		1,974,319
Purchase price of common stock, percentage	85.00%
Subsequent offering period	6 months
Restricted Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation		$ 2.1
Expected weighted average period		1 year

Stock-based Compensation - Su_3

Stock-based Compensation - Summary of Options to Purchase Common Stock (Details) - 2019 Equity Incentive Plan $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Outstanding, beginning balance | shares	8,442,824
Number of Options, Granted | shares	2,536,087
Number of Options, Exercised | shares	(583,591)
Number of Options, Forfeited | shares	(362,050)
Number of Options, Outstanding, ending balance | shares	10,033,270
Number of Options, Exercisable | shares	2,834,348
Number of Options, Vested and expected to vest | shares	10,033,270
Weighted average exercise price, Outstanding, beginning balance | $ / shares	$ 12.79
Weighted average exercise price, Granted | $ / shares	21.42
Weighted average exercise price, Exercised | $ / shares	9.77
Weighted average exercise price, Forfeited | $ / shares	16.53
Weighted average exercise price, Outstanding, ending balance | $ / shares	15.01
Weighted average exercise price, Exercisable | $ / shares	12.22
Weighted average exercise price, Vested and expected to vest | $ / shares	$ 15.01
Weighted Average Remaining Contractual Term, Outstanding (in years)	8 years 8 months 12 days
Weighted Average Remaining Contractual Term, Exercisable (In years)	8 years 3 months 18 days
Weighted Average Remaining Contractual Term, Vested and expected to vest (In years)	8 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding | $	$ 6,402
Aggregate Intrinsic Value, Exercisable | $	3,017
Aggregate Intrinsic Value, Vested or expected to vest | $	$ 6,402

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	Jan. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Follow-on-offering
Related Party Transaction [Line Items]
Public offerings	9,602,500
Share price	$ 25
Follow-on-offering | Director
Related Party Transaction [Line Items]
Public offerings	20,000
Share price	$ 25
Two Thousand Fourteen Adimab Agreement
Related Party Transaction [Line Items]
Related party transaction expenses		$ 0		$ 0
Adimab
Related Party Transaction [Line Items]
Related party transaction expenses			$ 2,000,000		$ 2,800,000
Accrued liabilities due to related parties		0		0		$ 0
Adimab | Maximum
Related Party Transaction [Line Items]
Future milestone payments owed		$ 3,500,000		$ 3,500,000

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	10,474,613	7,161,541	10,474,613	7,161,541
Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	415,521	1,191,750	415,521	1,191,750
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	10,033,270	5,918,124	10,033,270	5,918,124
Shares Committed Under ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive shares	25,822	51,667	25,822	51,667

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) $ in Millions	1 Months Ended	9 Months Ended
	Oct. 31, 2020USD ($)ft²	Sep. 30, 2020
Subsequent Event [Line Items]
Lease, description		In October 2020, the Company signed a lease agreement to lease approximately 18,700 square feet in Newark, CA that will be used for laboratory and office space. The lease commences on December 1, 2020 and is over a 7-year 2-month term with an option to extend for an additional five years. Fixed rent payments under the initial term of the lease are approximately $7.7 million. The Company will also pay a proportionate share of the facility’s operating expenses.
Subsequent Event [Member]
Subsequent Event [Line Items]
Area of property | ft²	18,700
Lease commencement, date	Dec. 1, 2020
Lease, term	7 years 2 months
Fixed rent payments | $	$ 7.7
Lease, option to extend	true
Extend for an additional lease term	5 years