Investment Securities Summary of Amortized Cost and Fair Values of Corporate Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,524,160
Corporate debt securities	2,483,443
Corporate Debt Securities Issued by Financial Institutions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	105,593	$ 108,014
Corporate debt securities	103,875	105,407
Single-issuer Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,770	43,746
Corporate debt securities	40,720	39,829
Subordinated Debt
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,787	46,231
Corporate debt securities	44,399	46,723
Senior Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,036	18,037
Corporate debt securities	18,334	18,433
Pooled Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Corporate debt securities	422	422
Other Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,002	4,002
Corporate debt securities	4,002	4,002
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	109,595	112,016
Corporate debt securities	$ 107,877	$ 109,409