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Cover
Oct. 13, 2021
Cover [Abstract]  
Document Type 8-K
Amendment Flag false
Document Period End Date Oct. 13, 2021
Entity File Number 001-36423
Entity Registrant Name HENNESSY ADVISORS, INC.
Entity Central Index Key 0001145255
Entity Tax Identification Number 68-0176227
Entity Incorporation, State or Country Code CA
Entity Address, Address Line One 7250 Redwood Blvd.
Entity Address, Address Line Two Suite 200
Entity Address, City or Town Novato
Entity Address, State or Province CA
Entity Address, Postal Zip Code 94945
City Area Code 415
Local Phone Number 899-1555
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common stock, no par value
Trading Symbol HNNA
Security Exchange Name NASDAQ
Entity Emerging Growth Company false