Investments - Summary of Investments in Private Equity Funds (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investment in Private Equity Funds	$ 58,507	$ 59,856
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in Private Equity Funds	9,800	13,812
Trilantic IV and V [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in Private Equity Funds	5,125	6,421
Glisco II, III and IV [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in Private Equity Funds	3,880	6,558
ECP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in Private Equity Funds	$ 795	$ 833