Securities (Amortized Cost and Estimated Fair Values of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale, Amortized Cost
Due in one year or less	$ 1,034
Due after one year through five years	86,362
Due after five years through ten years	129,521
Due after ten years	571,680
Total	788,597
Available-for-sale, Fair Value
Due in one year or less	1,039
Due after one year through five years	86,299
Due after five years through ten years	129,248
Due after ten years	562,540
Total	779,126
Held-to-maturity, Amortized Cost
Due after one year through five years	5,599
Due after five years through ten years	4,210
Due after ten years	84,800
Held-to-maturity Securities	94,609	$ 84,144
Held-to-maturity, Fair Value
Due after one year through five years	5,650
Due after five years through ten years	4,221
Due after ten years	84,725
Held-to-maturity Securities, Fair Value	$ 94,596	$ 85,647