Investment Securities - Amortized cost and fair value of debt securities (Details) - USD ($)
$ in Thousands
Sep. 30, 2020
Dec. 31, 2019
Available for Sale Amortized Cost    
Due in one year or less, Amortized Cost $ 0  
Due after one year through five years, Amortized Cost 4,185  
Due after five years through ten years, Amortized Cost 6,961  
Due after ten years, Amortized Cost 41,861  
Available for Sale, Amortized Cost 53,007  
Amortized Cost 76,325 $ 56,713
Available for Sale Fair Value    
Due in one year or less, Fair Value 0  
Due after one year through five years, Fair Value 4,341  
Due after five years through ten years, Fair Value 7,595  
Due after ten years, Fair Value 44,144  
Available for Sale, Fair Value 56,080  
Fair Value 79,712 58,417
Mortgage-backed securities    
Available for Sale Amortized Cost    
Amortized Cost 23,318 20,323
Available for Sale Fair Value    
Fair Value $ 23,632 $ 20,482