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Investment Advisory Agreements - Additional Information (Detail) - Funds		9 Months Ended
	Feb. 28, 2014	Jun. 30, 2015
Investments Schedule [Abstract]
Number of Hennessy funds to which company provides investment advisory services		16
Notice period for termination of agreement		60 days
Agreement term	2 years
Initial management agreement renewal period	1 year

X

- Definition

Initial management agreement renewal period.

+ References

No definition available.

+ Details

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

X

- Definition

Initial period of management agreements.

+ References

No definition available.

+ Details

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

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

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- References

No definition available.

+ Details

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