Pension and Other Postretirement Benefit Plans - Change in Benefit Obligation and Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Retirement Plan [Member]
Projected benefit obligation at beginning of year	$ 22,443	$ 20,344
Interest cost	652	797
Actuarial (gain) loss	2,109	2,265
Benefits paid	(977)	(963)
Projected benefit obligation at end of year	24,227	22,443
Market value of assets at beginning of year	25,505	22,419
Actual return on plan assets	3,192	4,049
Benefits paid	(977)	(963)
Market value of plan assets at end of year	27,720	25,505
Accrued pension asset/liability included in other assets	3,493	3,062
Other Postretirement Benefits Plan [Member]
Projected benefit obligation at beginning of year	8,762	8,518
Service cost	274	280
Interest cost	259	341
Actuarial (gain) loss	1,599	(301)
Benefits paid	(95)	(76)
Projected benefit obligation at end of year	10,799	8,762
Market value of assets at beginning of year	0	0
Benefits paid	(95)	(76)
Market value of plan assets at end of year	0	0
Employer contributions	95	76
Accrued pension cost included in other liabilities	10,799	8,762
Directors' Plan [Member]
Projected benefit obligation at beginning of year	2,290	2,265
Service cost	15	39
Interest cost	64	86
Actuarial (gain) loss	51	44
Benefits paid	(144)	(144)
Projected benefit obligation at end of year	2,276	2,290
Market value of assets at beginning of year	0	0
Benefits paid	(144)	(144)
Market value of plan assets at end of year	0	0
Employer contributions	144	144
Accrued pension cost included in other liabilities	$ 2,276	$ 2,290