Investments of Operating Entities and Consolidated Funds - Securities Sold, Not Yet Purchased (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Investments Sold, Not yet Purchased [Line Items]
Securities owned, at fair value		$ 610,234	$ 792,206
Securities sold, not yet purchased, at fair value		257,159	207,875
Merger Master
Investments Sold, Not yet Purchased [Line Items]
Securities owned, at fair value		157,921	136,893
Corporate Bonds
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value	[1]	$ 58	$ 60
Securities sold, not yet purchased, interest rate		5.55%	5.55%
Common Stock
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		$ 257,101	$ 207,815
Common Stock | Merger Master
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		$ 73,800	$ 39,900

[1] As of December 31, 2015 and 2014, the maturity was January 2026 with an interest rate of 5.55%