Securities (Details) - Remaining Contractual Maturity of Securities - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-Sale Securities, Amortized Cost Basis [Abstract]
One year or less	$ 73,669
After one year to five years	429,166
After five years to ten years	2,592
After ten years	47,682
Securities that do not have a single contractual maturity date	1,404,475
Amortized Cost	1,957,584	$ 1,324,146
Available-for-Sale Securities, Fair Value [Abstract]
One year or less	71,428
After one year to five years	416,112
After five years to ten years	2,513
After ten years	46,231
Securities that do not have a single contractual maturity date	1,383,166
Total	1,919,450	1,306,636
Held-to-Maturity Securities, Amortized Cost [Abstract]
One year or less	2,336
After one year to five years	6,834
After five years to ten years	2,975
After ten years	10,146
Securities that do not have a single contractual maturity date	0
Total	22,291	23,152
Held-to-Maturity Securities, Fair Value [Abstract]
One year or less	1,909
After one year to five years	5,583
After five years to ten years	2,431
After ten years	8,289
Securities that do not have a single contractual maturity date	0
Total	$ 18,212	$ 20,054