Securities (Details) - Remaining Contractual Maturity of Securities - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Available-for-sale Securities, Amortized Cost Basis [Abstract]
One year or less	$ 114,934
After one year to five years	104,940
After five years to ten years	177,819
After ten years	48,262
Securities that do not have a single contractual maturity date	708,170
Total	1,154,125	$ 1,192,322
Available-for-sale Securities, Fair Value [Abstract]
One year or less	112,254
After one year to five years	102,493
After five years to ten years	173,672
After ten years	47,137
Securities that do not have a single contractual maturity date	706,851
Total available-for-sale securities	1,142,407	1,187,009
Held-to-maturity Securities, Amortized Cost [Abstract]
One year or less	2,330
After one year to five years	8,497
After five years to ten years	4,947
After ten years	8,518
Securities that do not have a single contractual maturity date	0
Total	24,292	26,555
Held-to-maturity Securities, Fair Value [Abstract]
One year or less	2,354
After one year to five years	8,585
After five years to ten years	4,999
After ten years	8,607
Securities that do not have a single contractual maturity date	0
Total	$ 24,545	$ 27,670