Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Credit Facility [Line Items]
Description	On July 15, 2009, Duff & Phelps, LLC entered into a credit agreement with Bank of America, N.A., as administrative agent and the lenders from time to time party thereto, as amended by (i) the first amendment to the credit agreement dated as of November 8, 2010, (ii) the second amendment to credit agreement dated as of February 23, 2011, (iii) the third amendment to credit agreement dated as of August 15, 2011 and (iv) the fourth amendment to credit agreement dated as of October 13, 2011 (collectively, the “Credit Agreement”). The Credit Agreement provides for a $75,000 senior secured revolving credit facility ("Credit Facility"), including a $10,000 sub-limit for the issuance of letters of credit. The proceeds of the facility are permitted to be used for working capital, permitted acquisitions and general corporate purposes. The maturity date is October 13, 2016. Amounts borrowed may be voluntarily prepaid at any time without penalty or premium, subject to customary breakage costs. There was $22,500 outstanding under the Credit Facility as of December 31, 2012. As of December 31, 2012, the Company had $2,397 of outstanding letters of credit issued against the Credit Facility. These letters of credit were issued in connection with real estate leases.
Maximum borrowing capacity	$ 75,000
Sub-limit for the issuance of letters of credit	10,000
Maturity date	Oct. 13, 2016
Long-term debt	22,500	0
Amount of outstanding letters of credit	$ 2,397
Interest rate description	Loans under the Credit Facility will, at the Company's option, bear interest on the principal amount outstanding at either (a) a rate equal to LIBOR, plus an applicable margin or (b) a base rate, plus an applicable margin. The applicable margin rate is based on the Company's most recent consolidated leverage ratio and ranges from 1.25% to 2.25% per annum for the LIBOR rate or 0.25% to 1.25% per annum for the base rate. In addition, the Company is required to pay an unused commitment fee on the actual daily amount of the unutilized portion of the commitments of the lenders at a rate ranging from 0.30% to 0.50% per annum, based on the Company's most recent consolidated leverage ratio. Based on the Company's consolidated leverage ratio at December 31, 2012, the Company qualifies for the 1.25% applicable margin for the LIBOR rate or 0.25% applicable margin for the base rate, and 0.30% for the unused commitment fee.
Covenants	In addition, the Credit Agreement contains financial covenants that do not permit (i) a total leverage ratio of greater than 3.00 to 1.00 until the quarter ending March 31, 2013; and 2.75 to 1.00 thereafter and (ii) a consolidated fixed charge coverage ratio of less than 1.15 to 1.00 beginning July 1, 2011 through and including June 30, 2012; 1.20 to 1.00 beginning July 1, 2012 through and including September 30, 2013; and 1.25 to 1.00 thereafter. The financial covenants are tested on the last day of each fiscal quarter based on the last four fiscal quarter periods.
Line of Credit Facility, Covenant Compliance	Management believes that the Company was in compliance with all of its covenants as of December 31, 2012.