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v3.25.1

Income Taxes - Narrative (Detail) | 3 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024
Income Tax Disclosure [Abstract] |  |
Unconsolidated effective income tax rate | 26.90% | 26.30%

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- Definition Effective Income Tax Rate Reconciliation, Not Including Non-Controlling Interest, Percent + References No definition available. + Details
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Namespace Prefix: | dhil_
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Balance Type: | na
Period Type: | duration

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