Investments of Operating Entities and Consolidated Funds - Operating Entities - Equity Method Investment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Net gains (losses) on other investments	$ 4,300	$ 4,000	$ 23,600	$ 10,500
Equity method investments	40,096		40,096		$ 38,681
Starboard Value LP
Schedule of Equity Method Investments [Line Items]
Equity method investments	30,793		30,793		31,528
Healthcare Royalty GP III, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	2,205		2,205		2,213
RCG Longview Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	0		0		268
Healthcare Royalty GP, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	1,056		1,056		920
Healthcare Royalty GP II, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	242		242		269
Healthcare Royalty GP IV, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	1,745		1,745		304
RCG Longview Debt Fund IV Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	331		331		331
HCR Overflow Fund GP, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	843		843		740
RCG Longview Equity Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	0		0		105
HCR Stafford Fund GP, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	2,022		2,022		1,025
Liberty Harbor North
Schedule of Equity Method Investments [Line Items]
Equity method investments	222		222		222
Equity Method Investee, Other
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 637		$ 637		$ 756