Investments of Operating Entities and Consolidated Funds - Merger Master Derivatives (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Asset		$ 25,125	$ 69,177
Derivative Liability		16,082	42,750
Merger Master
Derivative [Line Items]
Derivative Asset		8,770	122,551
Derivative Liability		1,728	2,718
Option
Derivative [Line Items]
Derivative Liability	[1]	13,211	41,563
Option | Merger Master
Derivative [Line Items]
Derivative Liability		1,430	1,256
Options
Derivative [Line Items]
Derivative Asset	[2]	23,130	58,172
Options | Merger Master
Derivative [Line Items]
Derivative Asset		3,450	108,063
Swaps
Derivative [Line Items]
Derivative Asset		917	10,942
Derivative Liability		2,162	71
Swaps | Merger Master
Derivative [Line Items]
Derivative Asset		5,320	14,488
Derivative Liability		28	1,249
Currency Forwards
Derivative [Line Items]
Derivative Asset		1	5
Derivative Liability		709	874
Currency Forwards | Merger Master
Derivative [Line Items]
Derivative Liability		$ 270	$ 213

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

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