Supplemental Compensation Plans, Components of Net Periodic Benefit Cost and Additional Information (Details) - Pension Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Salary Continuation Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 213	$ 174	$ 99
Interest cost	221	185	171
Amortization of prior service cost	2	2	61
Recognized actuarial loss (gain)	87	101	58
Net periodic benefit cost	523	462	389
Additional Information [Abstract]
Minimum benefit obligation at year end	5,871	5,322	5,419	$ 4,523
Increase (decrease) in minimum liability included in other comprehensive income (loss)	298	(287)	827
Directors' Retirement Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	2	12	11
Interest cost	28	25	27
Recognized actuarial loss (gain)	0	0	0
Net periodic benefit cost	30	37	38
Additional Information [Abstract]
Minimum benefit obligation at year end	820	787	856	$ 830
Increase (decrease) in minimum liability included in other comprehensive income (loss)	$ 62	$ (36)	$ 18