Investment Securities Summary of Amortized Cost and Fair Values of Corporate Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,463,732
Corporate debt securities	2,485,585
Corporate Debt Securities Issued by Financial Institutions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	105,474	$ 96,301
Corporate debt securities	103,220	92,920
Single-issuer Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,720	44,648
Corporate debt securities	39,253	39,106
Subordinated Debt
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,715	39,610
Corporate debt securities	44,660	40,779
Senior Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,039	12,043
Corporate debt securities	18,601	12,329
Pooled Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Corporate debt securities	706	706
Other Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,021	4,035
Corporate debt securities	4,021	4,035
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	109,495	100,336
Corporate debt securities	$ 107,241	$ 96,955