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Investment Advisory Agreements - Additional Information (Detail) | 12 Months Ended
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Sep. 30, 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

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- 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

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- 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