Derivative Instruments - Forward starting interest rate swap transactions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Derivative
Original Notional Amount	$ 302,000,000	$ 265,000,000
Interest rate swap
Derivative
Original Notional Amount	25,000,000
Cash flow hedge | Interest rate swap | FHLB 90-day advance
Derivative
Original Notional Amount	225,000,000
Cash flow hedge | Interest rate swap | FHLB 90-day advance | July 1, 2016
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	5 years
Cash flow hedge | Interest rate swap | FHLB 90-day advance | August 25, 2017
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	7 years
Cash flow hedge | Interest rate swap | FHLB 90-day advance | August 25, 2017 2
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	7 years
Cash flow hedge | Interest rate swap | FHLB 90-day advance | January 2, 2019
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	15 years
Cash flow hedge | Interest rate swap | FHLB 90-day advance | December 27, 2019
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	3 years
Cash flow hedge | Interest rate swap | FHLB 90-day advance | January 2 2020
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	15 years
Cash flow hedge | Interest rate swap | FHLB 90-day advance | April 15 2020
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	5 years
Cash flow hedge | Interest rate swap | FHLB 90-day advance | April 29 2020
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	5 years
Cash flow hedge | Interest rate swap | FHLB 90-day advance | August 26 2020
Derivative
Original Notional Amount	$ 25,000,000
Duration of Borrowing (years)	15 years