XML 12 R43.htm IDEA: XBRL DOCUMENT
v3.20.1

Income Taxes - Narrative (Detail) | 3 Months Ended
--- | ---
Mar. 31, 2020 | Mar. 31, 2019
Income Tax Disclosure [Abstract] |  |
Unconsolidated effective income tax rate | 28.00% | 25.70%

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: | num: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