Investments Schedule of Equity Method Investment Ownership (Details) $ in Millions	Sep. 30, 2024 USD ($)
Schedule of Equity Method Investments [Line Items]
Equity method investment, deferred compensation plans	$ 8.4
DMHF
Schedule of Equity Method Investments [Line Items]
Ownership percentage	84.00%
Large Cap Fund
Schedule of Equity Method Investments [Line Items]
Ownership percentage	44.00%
Diamond Hill International Fund
Schedule of Equity Method Investments [Line Items]
Ownership percentage	42.00%

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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