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Significant Accounting Policies - Assets under Management (AUM) Subject to Incentive Fees and Incentive Fees (Detail)	3 Months Ended
	Mar. 31, 2021 USD ($)
Quarter Ending December 31, 2019
Principal Transaction Revenue [Line Items]
AUM subject to performance-based fees	$ 67,514,790
Unearned performance-based fees	125,672
Quarter Ending September 30, 2021
Principal Transaction Revenue [Line Items]
AUM subject to performance-based fees	375,886,495
Unearned performance-based fees	9,928,373
Total
Principal Transaction Revenue [Line Items]
AUM subject to performance-based fees	443,401,285
Unearned performance-based fees	$ 10,054,045

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- Definition

Assets under management (AUM) subject to variable rate fees and variable rate fees.

+ References

No definition available.

+ Details

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Namespace Prefix:	dhil_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- Definition

Potential Variable Fees Based Upon Current Investment Results

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No definition available.

+ Details

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Namespace Prefix:	dhil_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

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.

+ References

No definition available.

+ Details

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

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- Details

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Namespace Prefix:
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- Details

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- Details

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