Subsequent Events (Details) - Subsequent Event $ / shares in Units, $ in Millions	Feb. 25, 2021 $ / shares	Feb. 02, 2021 USD ($) payment
Subsequent Event [Line Items]
Dividend declared (in dollars per share) \| $ / shares	$ 1.00
Acquired Funds \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Subsequent Event [Line Items]
Consideration received		$ 9.0
Number of additional payments \| payment		2
Additional payment amount		$ 13.0
Term of additional payment		1 year

Disposal Group, Including Discontinued Operation, Additional Consideration

No definition available.

Name:	dhil_DisposalGroupIncludingDiscontinuedOperationAdditionalConsideration
Namespace Prefix:	dhil_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Disposal Group, Including Discontinued Operation, Additional Consideration, Term

+ References

No definition available.

+ Details

Name:	dhil_DisposalGroupIncludingDiscontinuedOperationAdditionalConsiderationTerm
Namespace Prefix:	dhil_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Disposal Group, Including Discontinued Operation, Number Of Additional Payments

+ References

No definition available.

+ Details

Name:	dhil_DisposalGroupIncludingDiscontinuedOperationNumberOfAdditionalPayments
Namespace Prefix:	dhil_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: