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Investment Advisory Agreements - Additional Information (Detail)	6 Months Ended
	Mar. 31, 2016 Funds
Investments Schedule [Abstract]
Number of Hennessy funds to which company provides investment advisory services	16
Notice period for termination of agreement	60 days

X

- Definition

Notice period for termination of agreement.

+ References

No definition available.

+ Details

Name:	hnna_NoticePeriodForTerminationOfAgreement
Namespace Prefix:	hnna_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Number of open end mutual funds.

+ References

No definition available.

+ Details

Name:	hnna_NumberOfOpenEndMutualFunds
Namespace Prefix:	hnna_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

Name:	invest_InvestmentsScheduleAbstract
Namespace Prefix:	invest_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration