Securities (Details) - Remaining Contractual Maturity of Securities - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Available-for-sale Securities, Amortized Cost Basis [Abstract]
One year or less	$ 135,762
After one year to five years	246,191
After five years to ten years	13,658
After ten years	48,159
Securities that do not have a single contractual maturity date	713,764
Amortized Cost	1,157,534	$ 1,192,322
Available-for-sale Securities, Fair Value [Abstract]
One year or less	132,787
After one year to five years	240,797
After five years to ten years	13,358
After ten years	47,104
Securities that do not have a single contractual maturity date	717,372
Total available-for-sale securities	1,151,418	1,187,009
Held-to-maturity Securities, Amortized Cost [Abstract]
One year or less	2,223
After one year to five years	8,727
After five years to ten years	4,476
After ten years	8,297
Securities that do not have a single contractual maturity date	0
Amortized Cost	23,723	26,555
Held-to-maturity Securities, Fair Value [Abstract]
One year or less	2,222
After one year to five years	8,721
After five years to ten years	4,473
After ten years	8,292
Securities that do not have a single contractual maturity date	0
Total	$ 23,708	$ 27,670