XML 57 R45.htm IDEA: XBRL DOCUMENT
v3.21.2

Income Taxes - Narrative (Detail) | 9 Months Ended
--- | ---
Sep. 30, 2021 | Sep. 30, 2020
Income Tax Disclosure [Abstract] |  |
Unconsolidated effective income tax rate | 27.00% | 28.00%

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

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