Investments of Operating Entities and Consolidated Funds - Merger Master Derivatives (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative Asset		$ 39,754	$ 25,125
Derivative Liability		32,755	16,082
Merger Master
Derivative [Line Items]
Derivative Asset		2,790	8,770
Derivative Liability		14,841	1,728
Option
Derivative [Line Items]
Derivative Liability	[1]	26,162	13,211
Option | Merger Master
Derivative [Line Items]
Derivative Liability		856	1,430
Options
Derivative [Line Items]
Derivative Asset	[2]	34,769	23,130
Options | Merger Master
Derivative [Line Items]
Derivative Asset		2,691	3,450
Swaps
Derivative [Line Items]
Derivative Asset		4,242	917
Derivative Liability		6,502	2,162
Swaps | Merger Master
Derivative [Line Items]
Derivative Asset		99	5,320
Derivative Liability		49	28
Currency Forwards
Derivative [Line Items]
Derivative Asset		640	1
Derivative Liability		91	709
Currency Forwards | Merger Master
Derivative [Line Items]
Derivative Liability		$ 13,936	$ 270

[1] Includes index, equity, commodity future and cash conversion options.

[2] Includes index, equity, commodity future and cash conversion options.