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Subsequent Event (Details)	3 Months Ended
	Mar. 31, 2013
Subsequent Event (Textual) [Abstract]
Revenue generated from accounts	2.60%

X

- Definition

Entity wide revenue percentage from two accounts.

+ References

No definition available.

+ Details

Name:	dhil_EntityWideRevenuePercentageFromTwoAccounts
Namespace Prefix:	dhil_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	dhil_SubsequentEventTextualAbstract
Namespace Prefix:	dhil_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration