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Significant Accounting Policies - Assets under Management (AUM) Subject to Incentive Fees and Incentive Fees (Detail) | 6 Months Ended
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Jun. 30, 2018 USD ($)
Quarter Ending December 31, 2018 |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | $ 103,406,795
Unearned variable rate fees | 1,352,041
Quarter Ending September 30, 2019 |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | 35,092,891
Unearned variable rate fees | 559,421
Quarter Ending March 31, 2020 |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | 12,800,012
Unearned variable rate fees | 0
Quarter Ending September 30, 2021 |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | 263,730,212
Unearned variable rate fees | 3,578,497
Total |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | 415,029,910
Unearned variable rate fees | $ 5,489,959

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- Definition Assets under management (AUM) subject to variable performance fees and variable performance 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 + References No definition available. + Details
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Namespace Prefix: | dhil_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- 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_
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Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
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- Details
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Data Type: | na
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- Details
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- Details
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- Details
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Period Type: |