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Operating Leases (Details Textual)	9 Months Ended	12 Months Ended
	Sep. 30, 2012 sqft Location	Dec. 31, 2011
Operating Leases (Textual) [Abstract]
Area of operating lease	25,500
Number of office space locations	2
Operating expenses	9.69	9.60

X

- Definition

Operating expenses per square foot.

+ References

No definition available.

+ Details

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Namespace Prefix:	dhil_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Area leased by company as of balance sheet date.

+ References

No definition available.

+ Details

Name:	dhil_OperatingLeases
Namespace Prefix:	dhil_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

X

- Details

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

X

- Definition

The number of units (items of property) under operating lease arrangements.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant