Pension and Other Postretirement Benefits - The Components of the Net Pension Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Directors' Plan [Member]
Service cost	$ 15	$ 39	$ 42
Interest cost	64	86	78
Amortization of unrecognized (gain) loss	(55)	(141)	(91)
Amortization of past service credit			12
Net pension (benefit) expense	24	(16)	41
Current year actuarial (gain) loss	51	44	(184)
Amortization of actuarial gain (loss)	(55)	(141)	(91)
Total recognized in other comprehensive income	106	185	(105)
Total recognized in net pension cost (benefit) and other comprehensive loss	130	169	(64)
Amortization of prior service credit			(12)
Amortization of actuarial gain (loss)	55	141	91
Retirement Plan [Member]
Interest cost	652	797	781
Amortization of unrecognized (gain) loss	444	269	621
Expected return on plan assets	(1,028)	(1,088)	(1,452)
Net pension (benefit) expense	68	(22)	(50)
Current year actuarial (gain) loss	(54)	(696)	(2,307)
Amortization of actuarial gain (loss)	(444)	(269)	(621)
Total recognized in other comprehensive income	(498)	(965)	(2,928)
Total recognized in net pension cost (benefit) and other comprehensive loss	(430)	(987)	(2,978)
Amortization of actuarial gain (loss)	444	269	621
Other Post Retirement Benefit Plan Defined Benefit [Member]
Service cost	274	280	350
Interest cost	259	341	307
Amortization of unrecognized (gain) loss			33
Amortization of past service credit	(85)	(85)	(85)
Net pension (benefit) expense	448	536	605
Current year actuarial (gain) loss	1,599	(301)	(1,155)
Amortization of actuarial gain (loss)			33
Total recognized in other comprehensive income	1,684	(216)	(1,103)
Total recognized in net pension cost (benefit) and other comprehensive loss	2,132	320	(498)
Amortization of prior service credit	$ 85	$ 85	85
Amortization of actuarial gain (loss)			$ (33)