Investment Securities - Amortized Cost and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 385
Due after one year through five years	3,925
Due after five years through ten years	18,246
Due after ten years	44,237
Total excluding mortgage-backed securities	66,793
Mortgage-backed securities	305,438
Amortized Cost	372,231	$ 346,874
Fair Value
Due in one year or less	386
Due after one year through five years	3,969
Due after five years through ten years	18,499
Due after ten years	45,033
Total excluding mortgage-backed securities	67,887
Mortgage-backed securities	312,927
Investment securities available for sale	$ 380,814	$ 347,332