Investments of Operating Entities and Consolidated Funds - Equity Method Investments (Details) (USD $)						3 Months Ended				3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Clawback Obligation	Mar. 31, 2013 Operating Entities entities	Dec. 31, 2012 Operating Entities	Mar. 31, 2013 Operating Entities Net Gains (Losses) on Securities, Derivatives and Other Investments	Mar. 31, 2012 Operating Entities Net Gains (Losses) on Securities, Derivatives and Other Investments	Mar. 31, 2013 Operating Entities CBOE Stock Exchange, LLC	Mar. 31, 2013 Operating Entities RCG Longview Partners II, LLC Clawback Obligation Accounts Payable, Accrued Expenses and Other Liabilities	Mar. 31, 2013 Operating Entities Equity Method Investee, Exceeded Threshold for Income Test	Mar. 31, 2012 Operating Entities Equity Method Investee, Exceeded Threshold for Income Test	Mar. 31, 2013 Operating Entities Equity Method Investments	Dec. 31, 2012 Operating Entities Equity Method Investments	Mar. 31, 2013 Operating Entities Equity Method Investments RCG Longview Debt Fund IV Management, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments RCG Longview Debt Fund IV Management, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments Healthcare Royalty GP, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments Healthcare Royalty GP, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments Healthcare Royalty GP II, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments Healthcare Royalty GP II, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments CBOE Stock Exchange, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments CBOE Stock Exchange, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments Starboard Value L.P.	Dec. 31, 2012 Operating Entities Equity Method Investments Starboard Value L.P.	Mar. 31, 2013 Operating Entities Equity Method Investments RCG Longview Partners, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments RCG Longview Partners, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments RCG Longview Louisiana Manager, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments RCG Longview Louisiana Manager, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments RCG Urban American, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments RCG Urban American, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments RCG Urban American Management, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments RCG Urban American Management, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments RCG Longview Equity Management, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments RCG Longview Equity Management, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments Urban American Real Estate Fund II, L.P.	Dec. 31, 2012 Operating Entities Equity Method Investments Urban American Real Estate Fund II, L.P.	Mar. 31, 2013 Operating Entities Equity Method Investments RCG Kennedy House, LLC	Dec. 31, 2012 Operating Entities Equity Method Investments RCG Kennedy House, LLC	Mar. 31, 2013 Operating Entities Equity Method Investments Equity Method Investee, Other	Dec. 31, 2012 Operating Entities Equity Method Investments Equity Method Investee, Other	Mar. 31, 2013 Operating Entities Minimum	Mar. 31, 2013 Operating Entities Maximum
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage								9.70%																																30.00%	55.00%
Number of entities in which Company holds a majority				3
Other investments	$ 80,452,000	$ 84,930,000		$ 80,452,000	$ 84,930,000							$ 20,368,000	$ 26,462,000	$ 1,079,000	$ 1,954,000	$ 667,000	$ 642,000	$ 569,000	$ 1,086,000	$ 2,015,000	$ 2,058,000	$ 7,398,000	$ 12,757,000	$ 1,826,000	$ 1,535,000	$ 1,883,000	$ 1,866,000	$ 1,414,000	$ 1,380,000	$ 642,000	$ 545,000	$ 192,000	$ 285,000	$ 1,736,000	$ 1,636,000	$ 309,000	$ 377,000	$ 638,000	$ 341,000
Contractual obligation			6,200,000						6,200,000
Income (loss) from equity method investments						4,200,000	4,200,000
Equity Method Investment, Summarized Financial Information [Abstract]
Revenues										4,865,000	4,997,000
Expenses										1,327,000	1,374,000
Net realized and unrealized gains (losses)										107,000	37,000
Net Income										$ 3,645,000	$ 3,660,000