Investments - Summary of Other Equity Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	$ 58,507	$ 59,856
Luminis [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	6,517	5,999
Atalanta Sosnoff [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	13,291	13,963
ABS [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment	$ 38,699	$ 39,894