Investments of Operating Entities and Consolidated Funds - Consolidated Funds - Securities Owned at Fair Value (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Securities owned, at fair value		$ 355,496	$ 375,278
Preferred Stock
Investment Holdings [Line Items]
Securities owned, at fair value		4,393	4,393
Common Stock
Investment Holdings [Line Items]
Securities owned, at fair value		317,839	200,306
Government Securities
Investment Holdings [Line Items]
Securities owned, at fair value	[1]	$ 24,998	$ 161,607
Investment Interest Rate			0.00%
Government Securities | Minimum
Investment Holdings [Line Items]
Investment Interest Rate		0.00%
Government Securities | Maximum
Investment Holdings [Line Items]
Investment Interest Rate		8.75%
Corporate Bonds
Investment Holdings [Line Items]
Securities owned, at fair value	[2]	$ 2,655	$ 3,405
Corporate Bonds | Minimum
Investment Holdings [Line Items]
Investment Interest Rate		0.00%	0.00%
Corporate Bonds | Maximum
Investment Holdings [Line Items]
Investment Interest Rate		15.50%	15.00%
Warrants and Rights [Member]
Investment Holdings [Line Items]
Securities owned, at fair value		$ 5,611	$ 5,567
Consolidated Funds | Government Securities
Investment Holdings [Line Items]
Investment Interest Rate		0.00%	0.00%
Consolidated Funds | Corporate Bonds
Investment Holdings [Line Items]
Investment Interest Rate		6.25%	7.50%

[1] As of March 31, 2020, the maturity was April 2020 with an interest rate of 0%. As of December 31, 2019, maturities ranged from February 2020 to March 2020 and interest rates were 0%.

[2] As of March 31, 2020, the maturity was May 2026 with an interest rate of 6.25%. As of December 31, 2019, the maturity was July 2023 with an interest rate of 7.50%.