Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity - Securities Held-to-maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Held-to-maturity, Amortized Cost
Due 3 months or less	$ 910
Due after 3 months through one year	490
Due after one year through five years	9,762
Due after five years through ten years	30,900
Due after ten years	30,149
Agency mortgage-backed securities	223,453
Total	295,664
Held-to-maturity, Estimated Fair Value
Due 3 months or less	911
Due after 3 months through one year	498
Due after one year through five years	10,133
Due after five years through ten years	31,574
Due after ten years	30,815
Agency mortgage-backed securities	230,065
Total	$ 303,996	$ 368,107