Supplemental Compensation Plans, Components of Net Periodic Benefit Cost and Additional Information (Details) - Pension Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Salary Continuation Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 174	$ 99	$ 104
Interest cost	185	171	161
Amortization of prior service cost	2	61	88
Recognized actuarial loss (gain)	101	58	50
Net periodic benefit cost	462	389	403
Additional Information [Abstract]
Minimum benefit obligation at year end	5,322	5,419	4,523	$ 4,261
(Decrease) increase in minimum liability included in other comprehensive income (loss)	(287)	827	40
Directors' Retirement Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	12	11	11
Interest cost	25	27	27
Recognized actuarial loss (gain)	0	0	0
Net periodic benefit cost	37	38	38
Additional Information [Abstract]
Minimum benefit obligation at year end	787	856	830	$ 816
(Decrease) increase in minimum liability included in other comprehensive income (loss)	$ (36)	$ 18	$ 5