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Commitments and Contingencies - Narrative (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($)
Commitments and Contingencies Disclosure [Abstract] |
Carried interest subject to clawback provisions | $ 12
Estimated clawback amount | $ 1

X
- Definition Carried Interest Subject To Clawback Provisions + References No definition available. + Details
Name: | fhi_CarriedInterestSubjectToClawbackProvisions
Namespace Prefix: | fhi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Estimated Clawback Amount + References No definition available. + Details
Name: | fhi_EstimatedClawbackAmount
Namespace Prefix: | fhi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration