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Significant Accounting Policies - Assets under Management (AUM) Subject to Incentive Fees and Incentive Fees (Detail) | 9 Months Ended
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Sep. 30, 2018 USD ($)
Quarter Ending December 31, 2018 |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | $ 61,028,560
Unearned variable rate fees | 1,416,398
Quarter Ending September 30, 2019 |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | 36,681,776
Unearned variable rate fees | 708,542
Quarter Ending March 31, 2020 |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | 13,336,076
Unearned variable rate fees | 0
Quarter Ending September 30, 2021 |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | 284,788,511
Unearned variable rate fees | 4,145,635
Total |
Principal Transaction Revenue [Line Items] |
AUM subject to variable rate fees | 395,834,923
Unearned variable rate fees | $ 6,270,575

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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_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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