Investment Securities - Amortized Cost and Fair Value of Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost
Due in one year or less	$ 6,243
Due after one year through five years	1,910
Due after five years through ten years	33,362
Due after ten years	50,882
Total Amortized Cost	92,397
Mortgage-backed securities	338,990
Amortized Cost	431,387	$ 372,231
Fair Value
Due in one year or less	6,244
Due after one year through five years	1,948
Due after five years through ten years	33,152
Due after ten years	50,256
Total Fair Value	91,600
Mortgage-backed securities	342,129
Fair Value	$ 433,729	$ 380,814