Investments of Operating Entities and Consolidated Funds - Equity Method Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]
Other investments	$ 84,930,000	$ 59,943,000
Clawback Obligation [Member]
Schedule of Equity Method Investments [Line Items]
Contractual obligation	6,200,000
Operating Entities
Schedule of Equity Method Investments [Line Items]
Number of entities in which Company holds a majority	3
Other investments	84,930,000	59,943,000
Operating Entities | Net Gains (Losses) on Securities, Derivatives and Other Investments [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	15,600,000	5,400,000	3,400,000
Operating Entities | CBOE Stock Exchange, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	9.70%
Operating Entities | RCG Longview Partners II, LLC [Member] | Clawback Obligation [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member]
Schedule of Equity Method Investments [Line Items]
Contractual obligation	6,200,000
Operating Entities | Equity Method Investee, Exceeded Threshold for Income Test [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Total Assets	498,557,000	173,259,000
Equity Method Investment, Summarized Financial Information, Total Liabilities	20,170,000	26,016,000
Equity Method Investmetn, Summarized Financial Information, Equity	478,387,000	147,243,000
Equity Method Investment, Summarized Financial Information [Abstract]
Revenues	77,502,000	28,669,000	19,552,000
Expenses	61,727,000	42,959,000	20,031,000
Net realized and unrealized gains (losses)	5,575,000	9,365,000	1,969,000
Net Income	21,350,000	(4,925,000)
Operating Entities | Equity Method Investments [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	26,462,000	16,687,000
Operating Entities | Equity Method Investments [Member] | RCG Longview Debt Fund IV Management, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	1,954,000	1,980,000
Operating Entities | Equity Method Investments [Member] | Healthcare Royalty GP, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	642,000	513,000
Operating Entities | Equity Method Investments [Member] | Healthcare Royalty GP II, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	1,086,000	258,000
Operating Entities | Equity Method Investments [Member] | CBOE Stock Exchange, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	2,058,000	2,423,000
Operating Entities | Equity Method Investments [Member] | Starboard Value L.P. [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	12,757,000	3,693,000
Operating Entities | Equity Method Investments [Member] | RCG Longview Partners, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	1,535,000	1,569,000
Operating Entities | Equity Method Investments [Member] | RCG Longview Louisiana Manager, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	1,866,000	1,140,000
Operating Entities | Equity Method Investments [Member] | RCG Urban American, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	1,380,000	1,258,000
Operating Entities | Equity Method Investments [Member] | RCG Urban American Management, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	545,000	1,096,000
Operating Entities | Equity Method Investments [Member] | RCG Longview Equity Management, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	285,000	557,000
Operating Entities | Equity Method Investments [Member] | Urban American Real Estate Fund II, L.P. [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	1,636,000	1,541,000
Operating Entities | Equity Method Investments [Member] | RCG Kennedy House, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	377,000	323,000
Operating Entities | Equity Method Investments [Member] | Equity Method Investee, Other [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 341,000	$ 336,000
Operating Entities | Minimum
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	30.00%
Operating Entities | Maximum
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	55.00%