Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity – Securities Held-to-maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Held-to-maturity, Amortized Cost
Due 3 months or less	$ 502
Due after 3 months through one year	496
Due after one year through five years	3,189
Due after five years through ten years	21,740
Due after ten years	62,798
Agency mortgage-backed securities	309,616
Total	398,341	$ 324,010
Held-to-maturity, Estimated Fair Value
Due 3 months or less	502
Due after 3 months through one year	498
Due after one year through five years	3,219
Due after five years through ten years	22,207
Due after ten years	62,638
Agency mortgage-backed securities	305,228
Estimated Fair Value	$ 394,292	$ 318,748