Investment Securities - Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized cost
Due after one year through five years	$ 10,000
Due after five years through ten years	50,000
Due after ten years	18,972
Mortgage and asset-backed securities	227,047
Amortized cost	306,019	$ 274,957
Fair value
Due after one year through five years	10,092
Due after five years through ten years	49,886
Due after ten years	18,995
Mortgage and asset-backed securities	230,401
Fair value	$ 309,374	$ 277,439