Noncontrolling Interest Noncontrolling Interest Table (Details) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Ownership of New Class A Units [Roll Forward]
Common stock, shares, outstanding	42,134	41,317	40,264
Issuance of Class A common stock for follow-on offering, shares	3,707
Redemption of New Class A Units, shares	(4,407)
Issuance of Class A common stock for acquisitions, shares	227	1,180	176
Exchange of New Class A Units to shares of Class A common stock, shares	0	0	0
Net issuance of restricted stock awards, shares	1,315	1,966	1,596
Issuance of Class A common stock for exercises of stock options, shares	1	7	18
Stock Repurchased During Period, Shares	(309)	(2,024)	(451)
Forfeitures, shares	(248)	(312)	(286)
Common stock, shares, outstanding	42,420	42,134	41,317
Total ownership percentage of New Class A Units	100.00%	100.00%	100.00%
Parent [Member]
Ownership of New Class A Units [Roll Forward]
Common stock, shares, outstanding	31,646	30,166	27,290
Issuance of Class A common stock for follow-on offering, shares	3,707
Redemption of New Class A Units, shares	0
Issuance of Class A common stock for acquisitions, shares	227	1,180	176
Exchange of New Class A Units to shares of Class A common stock, shares	6,081	653	1,788
Net issuance of restricted stock awards, shares	1,315	1,966	1,596
Issuance of Class A common stock for exercises of stock options, shares	1	7	18
Stock Repurchased During Period, Shares	(309)	(2,024)	(451)
Forfeitures, shares	(248)	(302)	(251)
Common stock, shares, outstanding	42,420	31,646	30,166
Ownership percentage by Duff & Phelps Corporation	100.00%	75.10%	73.00%
Noncontrolling Interest [Member]
Ownership of New Class A Units [Roll Forward]
Common stock, shares, outstanding	10,488	11,151	12,974
Issuance of Class A common stock for follow-on offering, shares	0
Redemption of New Class A Units, shares	(4,407)
Issuance of Class A common stock for acquisitions, shares	0	0	0
Exchange of New Class A Units to shares of Class A common stock, shares	(6,081)	(653)	(1,788)
Net issuance of restricted stock awards, shares	0	0	0
Issuance of Class A common stock for exercises of stock options, shares	0	0	0
Stock Repurchased During Period, Shares	0	0	0
Forfeitures, shares	0	(10)	(35)
Common stock, shares, outstanding	0	10,488	11,151
Ownership percentage by noncontrolling owners	0.00%	24.90%	27.00%