Document and Entity Information
Jul. 07, 2022
Cover [Abstract]  
Amendment Flag false
Entity Central Index Key 0001528115
Document Type 8-K
Document Period End Date Jul. 07, 2022
Entity Registrant Name ANNEXON, INC.
Entity Incorporation State Country Code DE
Entity File Number 001-39402
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
Written Communications false
Soliciting Material false
Pre Commencement Tender Offer false
Pre Commencement Issuer Tender Offer false
Security 12b Title Common Stock, par value $0.001 per share
Trading Symbol ANNX
Security Exchange Name NASDAQ
Entity Emerging Growth Company false