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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

X

- 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

X

- Details

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