Investments - Summary of Other Equity Investments (Details) - Other Equity Method Investments [Member] - USD ($) $ in Thousands	Jun. 30, 2017	May 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	$ 67,671		$ 79,717
G5 Evercore [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	11,118	$ 11,555	26,016
ABS [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	36,519		38,982
Atalanta Sosnoff [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	14,477		14,719
Luminis [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	$ 5,557		$ 0