Investment Securities - Amortized Cost and Fair Value of Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 892
Due after one year through five years	3,939
Due after five years through ten years	7,336
Due after ten years	30,322
Debt Securities With Single Maturity Date, Amortized Cost	42,489
Mortgage-backed securities	312,764
Amortized cost	355,253	$ 346,874
Fair Value
Due In One Year or Less	895
Due After One Year Through Five Years	3,989
Due After Five Years Through Ten Years	7,505
Due After Ten Years	30,515
Debt Securities With Single Maturity Date, Fair Value	42,904
Mortgage-Backed Securities	320,697
Fair Value	$ 363,601	$ 347,332