Investments of Operating Entities and Consolidated Funds - Equity Method Investments (Details) (USD $)						3 Months Ended		9 Months Ended				9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Clawback Obligation [Member]	Sep. 30, 2012 Operating Entities [Member] entities	Dec. 31, 2011 Operating Entities [Member]	Sep. 30, 2012 Operating Entities [Member] Net Gains (Losses) on Securities, Derivatives and Other Investments [Member]	Sep. 30, 2011 Operating Entities [Member] Net Gains (Losses) on Securities, Derivatives and Other Investments [Member]	Sep. 30, 2012 Operating Entities [Member] Net Gains (Losses) on Securities, Derivatives and Other Investments [Member]	Sep. 30, 2011 Operating Entities [Member] Net Gains (Losses) on Securities, Derivatives and Other Investments [Member]	Sep. 30, 2012 Operating Entities [Member] CBOE Stock Exchange, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] RCG Longview Partners II, LLC [Member] Clawback Obligation [Member] Accounts Payable, Accrued Expenses and Other Liabilities [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investee, Exceeded Threshold for Income Test [Member]	Sep. 30, 2011 Operating Entities [Member] Equity Method Investee, Exceeded Threshold for Income Test [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] RCG Longview Debt Fund IV Management, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] RCG Longview Debt Fund IV Management, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] Healthcare Royalty GP, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] Healthcare Royalty GP, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] Healthcare Royalty GP II, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] Healthcare Royalty GP II, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] CBOE Stock Exchange, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] CBOE Stock Exchange, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] Starboard Value L.P. [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] Starboard Value L.P. [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] RCG Longview Partners, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] RCG Longview Partners, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] RCG Longview Louisiana Manager, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] RCG Longview Louisiana Manager, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] RCG Urban American, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] RCG Urban American, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] RCG Urban American Management, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] RCG Urban American Management, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] RCG Longview Equity Management, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] RCG Longview Equity Management, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] Urban American Real Estate Fund II, L.P. [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] Urban American Real Estate Fund II, L.P. [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] RCG Kennedy House, LLC [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] RCG Kennedy House, LLC [Member]	Sep. 30, 2012 Operating Entities [Member] Equity Method Investments [Member] Equity Method Investee, Other [Member]	Dec. 31, 2011 Operating Entities [Member] Equity Method Investments [Member] Equity Method Investee, Other [Member]	Sep. 30, 2012 Operating Entities [Member] Minimum [Member]	Sep. 30, 2012 Operating Entities [Member] Maximum [Member]
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	$ 70,151,000	$ 59,943,000		$ 70,151,000	$ 59,943,000									$ 20,001,000	$ 16,687,000	$ 1,490,000	$ 1,980,000	$ 662,000	$ 513,000	$ 443,000	$ 258,000	$ 2,165,000	$ 2,423,000	$ 7,651,000	$ 3,693,000	$ 1,698,000	$ 1,569,000	$ 1,490,000	$ 1,140,000	$ 1,347,000	$ 1,258,000	$ 538,000	$ 1,096,000	$ 226,000	$ 557,000	$ 1,564,000	$ 1,541,000	$ 396,000	$ 323,000	$ 331,000	$ 336,000
Contractual obligation			6,200,000								6,200,000
Income (loss) from equity method investments						1,500,000	500,000	9,400,000	2,900,000
Equity Method Investment, Summarized Financial Information [Abstract]
Revenues												5,877,000	232,000
Expenses												(588,000)	105,000
Net realized and unrealized gains (losses)												73,000	(21,000)
Net Income												$ 5,362,000	$ 316,000