Employee Benefit Plans (Schedule of Net Period Benefit Cost and Other Amounts Recognized in Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Executive Retirement Plan [Member]
Net period benefit cost
Service cost	$ 335	$ 308	$ 307
Interest cost	452	432	424
Recognized net actuarial loss	246	220	218
Amortization of prior service cost (credit)		7	19
Net periodic benefit cost	1,033	967	968
Changes in funded status recognized in other comprehensive loss, before taxes
Net actuarial (gain) loss arising during period	1,955	219	(32)
Amortization of net unrecognized actuarial loss	(246)	(220)	(218)
Amortization of prior service (cost) credit		(7)	(19)
Total recognized in OCI, before taxes	1,709	(8)	(269)
Total recognized in net periodic benefit cost and OCI, before taxes	2,742	959	699
Other Postretirement Benefit Plan [Member]
Net period benefit cost
Service cost	53	59	62
Interest cost	144	151	117
Recognized net actuarial loss	41	30	24
Amortization of prior service cost (credit)	(24)	(22)	(22)
Net periodic benefit cost	214	218	181
Changes in funded status recognized in other comprehensive loss, before taxes
Net actuarial (gain) loss arising during period	110	143	92
Amortization of net unrecognized actuarial loss	(41)	(30)	(24)
Amortization of prior service (cost) credit	24	22	22
Total recognized in OCI, before taxes	93	135	90
Total recognized in net periodic benefit cost and OCI, before taxes	$ 307	$ 353	$ 271