Investments - Gains and Losses Recognized in Gain (Loss) on Securities, Net (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
(Loss) Gain on Securities [Line Items]
Gain (Loss) on Securities, net	$ (15,840)	$ 1,679
Investments—Consolidated Investment Companies
(Loss) Gain on Securities [Line Items]
Unrealized Gains (Losses)	(10,352)	1,285
Net Realized Gains (Losses)	3	(461)
Gain (Loss) on Securities, net	(10,349)	824
Investments—Affiliates and Other
(Loss) Gain on Securities [Line Items]
Unrealized Gains (Losses)	(5,396)	877
Net Realized Gains (Losses)	(95)	(22)
Gain (Loss) on Securities, net	$ (5,491)	$ 855

The net realized gain (loss) on investments sold during the period, not including gains (losses) on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, which, for cash flow reporting, is a component of proceeds from investing activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainLossOnSaleOfInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

+ References

No definition available.

+ Details

Name:	us-gaap_MarketableSecuritiesGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of unrealized gain (loss) on investment in marketable security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(7)(c))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

Name:	us-gaap_MarketableSecuritiesUnrealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentAxis=fhi_InvestmentsConsolidatedInvestmentCompaniesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=fhi_InvestmentsAffiliatesAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: