Noncontrolling Interest Reconciliation of Income Before Taxes to Net Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Reconciliation of Income Before Taxes to Net Income [Line Items]
Income before income taxes									$ 46,323		$ 43,570		$ 42,849
Provision for Income Taxes for Entities Other Than DPC									(2,684)	[1],[2]	(826)	[1],[2]	(2,066)	[1],[2]
Income Before Taxes As Adjusted									43,639		42,744		40,783
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners									9.30%	[3]	26.00%	[3]	30.80%	[3]
Net income attributable to noncontrolling interest									4,037		11,115		12,581
Income Before Taxes, As Adjusted, Attributable to Parent									39,602		31,629		28,202
Provision for Income Taxes Attributable to Parent									(17,338)	[1],[4]	(13,015)	[1],[4]	(11,437)	[1],[4]
Net income attributable to Duff & Phelps Corporation	6,065	5,701	6,593	3,905	7,045	4,032	3,424	4,113	22,264		18,614		16,765
Provision for income taxes									$ 20,022		$ 13,841		$ 13,503

[1] (a)The consolidated provision for income taxes is equal to the sum of (i) the provision for income taxes for entities other than Duff & Phelps Corporation and (ii) the provision for income taxes of Duff & Phelps Corporation. The consolidated provision for income taxes totaled $20,022, $13,841 and $13,503 for the years ended December 31, 2012, 2011 and 2010, respectively.

[2] (b)The provision for income taxes for entities other than Duff & Phelps Corporation represents taxes imposed directly on Duff & Phelps, LLC, a wholly-owned subsidiary of D&P Acquisitions, and its subsidiaries, such as taxes imposed on certain domestic subsidiaries (e.g., Rash & Associates, L.P.), taxes imposed by certain foreign jurisdictions, and taxes imposed by certain local and other jurisdictions (e.g., New York City). Since Duff & Phelps, LLC is taxed as a partnership and a flow-through entity for U.S. federal and state income tax purposes, there is no provision for these taxes on income allocable to the noncontrolling interest.

[3] (d)Income before income taxes, as adjusted, is allocated to the noncontrolling interest based on the total New Class A Units vested for income tax purposes (“Tax-Vested Units”) owned by the noncontrolling interest as a percentage of the aggregate amount of all Tax-Vested Units. This percentage may not necessarily correspond to the total number of New Class A Units at the end of each respective period.

[4] (c)The provision of income taxes of Duff & Phelps Corporation includes all U.S. federal and state income taxes.