Investment Securities Summary of Amortized Cost and Fair Values of Corporate Debt Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,479,877
Corporate debt securities	2,509,035
Corporate Debt Securities Issued by Financial Institutions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	91,399	$ 96,301
Corporate debt securities	87,527	92,920
Single-issuer Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,697	44,648
Corporate debt securities	37,461	39,106
Subordinated Debt
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,662	39,610
Corporate debt securities	30,708	40,779
Senior Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,040	12,043
Corporate debt securities	18,652	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	4,020	4,035
Corporate debt securities	4,020	4,035
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	95,419	100,336
Corporate debt securities	$ 91,547	$ 96,955