XML 15 R1.htm IDEA: XBRL DOCUMENT v3.25.0.1
Cover Page - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Feb. 26, 2025
Jun. 28, 2024
Document Type 10-K    
Document Annual Report true    
Document Transition Report false    
Amendment Flag false    
Document Period End Date Dec. 31, 2024    
Document Fiscal Year Focus 2024    
Document Fiscal Period Focus FY    
Trading Symbol ANNX    
Entity Registrant Name ANNEXON, INC.    
Entity Central Index Key 0001528115    
Current Fiscal Year End Date --12-31    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Title of 12(b) Security Common Stock, par value $0.001 per share    
Security Exchange Name NASDAQ    
Entity File Number 001-39402    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 27-5414423    
Entity Address, Address Line One 1400 Sierra Point Parkway    
Entity Address, Address Line Two Bldg C    
Entity Address, Address Line Three Suite 200    
Entity Address, City or Town Brisbane    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 94005    
City Area Code 650    
Local Phone Number 822-5500    
Entity Small Business true    
Entity Emerging Growth Company false    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 477.2
ICFR Auditor Attestation Flag false    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Auditor Name KPMG LLP    
Auditor Location San Francisco, CA    
Auditor Firm ID 185    
Common Stock [Member]      
Entity Common Stock, Shares Outstanding   109,709,826  
Prefunded Warrant [Member]      
Entity Common Stock, Shares Outstanding   38,543,577