Investments of Operating Entities and Consolidated Funds - Consolidated Funds - Receivable on/Payable For Derivative Contracts (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Receivable on derivative contracts, at fair value		$ 83,867	$ 62,977
Payable for derivative contracts, at fair value		72,385	60,761
Merger Master
Derivative [Line Items]
Receivable on derivative contracts, at fair value		4,835	2,453
Payable for derivative contracts, at fair value		2,815	1,426
Options
Derivative [Line Items]
Receivable on derivative contracts, at fair value	[1]	58,334	60,066
Options | Merger Master
Derivative [Line Items]
Receivable on derivative contracts, at fair value		2,945	2,047
Option
Derivative [Line Items]
Payable for derivative contracts, at fair value	[2]	60,946	36,524
Option | Merger Master
Derivative [Line Items]
Payable for derivative contracts, at fair value		1,126	1,158
Currency Forwards
Derivative [Line Items]
Receivable on derivative contracts, at fair value		1,010	0
Payable for derivative contracts, at fair value		1,883	851
Swaps
Derivative [Line Items]
Receivable on derivative contracts, at fair value		24,523	2,911
Payable for derivative contracts, at fair value		9,469	23,169
Swaps | Merger Master
Derivative [Line Items]
Receivable on derivative contracts, at fair value		1,890	406
Payable for derivative contracts, at fair value		$ 1,689	$ 268

[1] Includes the volume of contracts for index, equity, commodity future and cash conversion options.

[2] Includes the volume of contracts for index, equity, commodity future and cash conversion options.