Investments of Operating Entities and Consolidated Funds - Equity Method Investments - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 40,858	$ 38,671
Equity Method Investment, Summarized Financial Information, Assets	1,374,077	1,189,669
Liabilities	205,873	244,088
Other than Temporary Impairment Losses, Investments	2,600	7,100
Equity Method Investee, Exceeded Threshold for Income Test [Member]
Schedule of Equity Method Investments [Line Items]
Equity	1,168,204	945,581
Revenue	200,854	105,499	$ 165,550
Expenses	(79,811)	(67,893)	(62,175)
Net realized and unrealized gain (loss)	221,616	95,855	133,695
Equity Method Investment, Summarized Financial Information, Income (Loss) from Continuing Operations	342,659	133,461	237,070
Equity method investment, summarized financial information, income tax expense (benefit)	(2,234)	(51)	(99)
Net Income	340,425	133,410	236,971
Surf House Ocean Views Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	7,804	7,589
Starboard Value LP
Schedule of Equity Method Investments [Line Items]
Equity method investments	24,292	12,699
RCG Longview Debt Fund V Partners, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	2,889	11,000
RCG Longview Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	583	1,167
Income (Loss) from Equity Method Investments	200
RCG Longview Debt Fund VI, LP
Schedule of Equity Method Investments [Line Items]
Equity method investments	0	1,254
Healthcare Royalty GP, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	108	149
Healthcare Royalty GP II, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	302	176
RCG Longview Debt Fund IV Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	331	331
Healthcare Royalty GP III, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	2,230	1,573
RCG Kennedy House, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	0	131
RCG Longview Equity Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	105	114
RCG LPP II GP, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	0	272
RCG Park Liberty GP Member Manager, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	0	1,248
HCR Stafford Fund GP, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	880	0
Equity Method Investee, Other
Schedule of Equity Method Investments [Line Items]
Equity method investments	1,042	968
Liberty Harbor North
Schedule of Equity Method Investments [Line Items]
Equity method investments	292	0
Net Gains (Losses) on Securities, Derivatives and Other Investments
Schedule of Equity Method Investments [Line Items]
Income (Loss) from Equity Method Investments	$ 24,600	6,400	$ 21,300
Minimum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	15.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	55.00%
Clawback Obligation
Schedule of Equity Method Investments [Line Items]
Other Commitment		6,500
Clawback Obligation | RCG Longview Partners II, LLC
Schedule of Equity Method Investments [Line Items]
Other Commitment		$ 6,500