Investments of Operating Entities and Consolidated Funds - Consolidated Funds - Receivable on/Payable For Derivative Contracts (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Receivable on derivative contracts, at fair value		$ 58,194	$ 62,977
Payable for derivative contracts, at fair value		62,054	60,761
Merger Master
Derivative [Line Items]
Receivable on derivative contracts, at fair value			2,453
Payable for derivative contracts, at fair value			1,426
Options
Derivative [Line Items]
Receivable on derivative contracts, at fair value	[1]	52,680	60,066
Options | Merger Master
Derivative [Line Items]
Receivable on derivative contracts, at fair value			2,047
Option
Derivative [Line Items]
Payable for derivative contracts, at fair value	[2]	53,700	36,524
Option | Merger Master
Derivative [Line Items]
Payable for derivative contracts, at fair value			1,158
Currency Forwards
Derivative [Line Items]
Receivable on derivative contracts, at fair value		870	0
Payable for derivative contracts, at fair value		717	851
Swaps
Derivative [Line Items]
Receivable on derivative contracts, at fair value		4,644	2,911
Payable for derivative contracts, at fair value		$ 7,514	23,169
Swaps | Merger Master
Derivative [Line Items]
Receivable on derivative contracts, at fair value			406
Payable for derivative contracts, at fair value			$ 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.