Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity - Securities Held-to-maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Held-to-maturity, Amortized Cost
Due after 3 months through one year	$ 493
Due after one year through five years	10,390
Due after five years through ten years	31,509
Due after ten years	26,399
Agency mortgage-backed securities	228,652
Total	297,443
Held-to-maturity, Estimated Fair Value
Due after 3 months through one year	499
Due after one year through five years	10,757
Due after five years through ten years	32,149
Due after ten years	27,025
Agency mortgage-backed securities	234,497
Total	$ 304,927	$ 368,107