Investments of Operating Entities and Consolidated Funds - Operating Entities - Securities Sold, Not Yet Purchased (Details) - USD ($)		Mar. 31, 2020	Dec. 31, 2019
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		$ 527,471,000	$ 451,836,000
Common Stock
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		460,059,000	425,448,000
Corporate Bonds
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value	[1]	$ 4,402,000	$ 5,933,000
Corporate Bonds | Minimum
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, interest rate		5.00%	4.88%
Corporate Bonds | Maximum
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, interest rate		6.75%	6.25%
US Government Debt Securities
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value	[2]	$ 48,073,000	$ 1,950,000
Government Securities | Minimum
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, interest rate		6.25%	7.00%
Government Securities | Maximum
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, interest rate		8.75%	8.25%
Preferred Stock
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		$ 6,405,000	$ 3,686,000
Warrants and Rights [Member]
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		$ 8,532,000	$ 14,819,000

[1] As of March 31, 2020, the maturities ranged from April 2020 to May 2067 and interest rates ranged from 5.00% to 6.75%. As of December 31, 2019, the maturities ranged from January 2024 to May 2037 and interest rates ranged from 4.88% to 6.25%.

[2] As of March 31, 2020, the maturities ranged from October 2024 to February 2048 and interest rates ranged from 6.25% to 8.75%. As of December 31, 2019, the maturities ranged from October 2024 to March 2038 and interest rates ranged from 7.00% to 8.25%.