XML 36 R1.htm IDEA: XBRL DOCUMENT v3.20.4
Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Feb. 15, 2021
Jun. 30, 2020
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2020    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Trading Symbol ALEC    
Entity File Number 001-38792    
Entity Tax Identification Number 82-2933343    
Entity Public Float     $ 1,375.6
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 Annual Report true    
Entity Registrant Name Alector, Inc.    
Entity Central Index Key 0001653087    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Common Stock, Shares Outstanding   79,584,442  
Security Exchange Name NASDAQ    
Title of 12(b) Security Common Stock    
Entity Interactive Data Current Yes    
Entity Well-known Seasoned Issuer No    
Entity Incorporation, State or Country Code DE    
Documents Incorporated by Reference

Portions of the registrant’s Definitive Proxy Statement relating to the registrant’s Annual Meeting of Shareholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated.