Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity – Securities Held-to-maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Held-to-maturity, Amortized Cost
Due after 3 months or less	$ 370
Due after 3 months through one year	505
Due after one year through five years	3,680
Due after five years through ten years	20,125
Due after ten years	64,452
Agency mortgage-backed securities	290,418
Total	379,550	$ 324,010
Held-to-maturity, Estimated Fair Value
Due 3 months or less	371
Due after 3 months through one year	506
Due after one year through five years	3,756
Due after five years through ten years	20,668
Due after ten years	64,208
Agency mortgage-backed securities	288,336
Estimated Fair Value	$ 377,845	$ 318,748