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Significant Accounting Policies - Summary of Investments Values Based Upon Level 1and Level 2 (Detail) (USD $) | Sep. 30, 2014 | Dec. 31, 2013
--- | --- | ---
Level 1 Inputs |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Value of Investment | $ 69,091,752 | $ 32,528,367
Level 2 Inputs |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Value of Investment | $ 4,711,277 | $ 3,001,461

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- Definition Value of investment. + 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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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration