Basis of Presentation Entry into a Definitive Merger Agreement (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Entry into a Material Merger Agreement [Line Items]
Description of proposed merger	On December 30, 2012, the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Duff & Phelps Acquisitions, LLC, a wholly owned subsidiary of the Company (“D&P Acquisitions”), Dakota Holding Corporation (“Parent”), Dakota Acquisition I, Inc., a wholly owned subsidiary of Parent (“Merger Sub I”), and Dakota Acquisition II, LLC, a wholly owned subsidiary of Merger Sub I (“Merger Sub II”), pursuant to which Merger Sub II will merge with and into D&P Acquisitions with D&P Acquisitions surviving, and immediately thereafter Merger Sub I will merge with and into the Company (the “Merger”) with the Company surviving as a wholly owned subsidiary of Parent.  Parent is owned by funds advised by Carlyle Investment Management, L.L.C. (d/b/a The Carlyle Group), Stone Point Capital LLC, Pictet & Cie, and The Edmond de Rothschild Group.
Sale of Stock, Price Per Share	$ 15.55
Merger agreement termination fee	$ 19,964
Senior secured first-lien loan facilities	424,000
Senior secured term loan facility	349,000
Senior secured revolving credit facilty	75,000
Senior secured revolving credit facility available at closing	$ 20,000
Description of debt financing commitment	The obligation of the Lenders to provide debt financing under the Debt Financing Commitment is subject to a number of conditions, exceptions and qualifications, including without limitation: (i) the absence of a material adverse effect on the Company since December 31, 2011, (ii) execution and delivery of definitive documentation with respect to the debt financing contemplated by the Debt Financing Commitment and otherwise mutually agreed, (iii) accuracy of certain specified representations and warranties in the loan documents and in the merger agreement, (iv) receipt of equity financing from the investors in an amount at least equal to a specified minimum, (v) certain marketing periods with respect to the financing shall have expired and (vi) consummation of the merger in accordance with the merger agreement. The final termination date for the Debt Financing Commitment is the earliest of (i) the consummation of the merger with or without the funding of the proposed credit facilities (or earlier termination of the merger agreement in accordance with its terms) and (ii) July 1, 2013.