Investments of Operating Entities and Consolidated Funds - Merger Master Derivatives (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative Asset		$ 32,220	$ 25,125
Derivative Liability		22,445	16,082
Merger Master
Derivative [Line Items]
Derivative Asset		4,393	8,770
Derivative Liability		37,850	1,728
Option
Derivative [Line Items]
Derivative Liability	[1]	19,779	13,211
Option | Merger Master
Derivative [Line Items]
Derivative Liability		194	1,430
Options
Derivative [Line Items]
Derivative Asset	[2]	22,501	23,130
Options | Merger Master
Derivative [Line Items]
Derivative Asset		4,291	3,450
Swaps
Derivative [Line Items]
Derivative Asset		9,440	917
Derivative Liability		2,231	2,162
Swaps | Merger Master
Derivative [Line Items]
Derivative Asset		102	5,320
Derivative Liability		347	28
Currency Forwards
Derivative [Line Items]
Derivative Asset		279	1
Derivative Liability		1	709
Currency Forwards | Merger Master
Derivative [Line Items]
Derivative Liability		$ 37,309	$ 270

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

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