Investments - Summary of Other Equity Investments (Details) - Other Equity Method Investments [Member] - USD ($) $ in Thousands	Sep. 30, 2017	May 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	$ 69,718		$ 79,717
G5 Evercore [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	12,238	$ 11,555	26,016
ABS [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	37,501		38,982
Atalanta Sosnoff [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	14,368		14,719
Luminis [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	$ 5,611		$ 0