Document and Entity Information	6 Months Ended
	Mar. 31, 2013	Apr. 10, 2013
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2013
Document Fiscal Period Focus	Q2
Trading Symbol	HNNA
Document Fiscal Year Focus	2013
Entity Registrant Name	HENNESSY ADVISORS INC
Entity Central Index Key	0001145255
Current Fiscal Year End Date	--09-30
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		5,884,172