Employee Benefits (Schedule of Net Funded (Unfunded) Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Qualified Pension Plan [Member]
Change in Benefit Obligation:
Benefit obligation at beginning of period	$ 72,951	$ 67,550
Service cost	2,149	2,148	$ 2,459
Interest cost	2,673	2,576	2,928
Actuarial loss	7,017	3,888
Benefits paid	(3,936)	(3,072)
Administrative expenses	(131)	(139)
Benefit obligation at end of period	80,723	72,951	67,550
Change in Plan Assets:
Fair value of plan assets at beginning of period	75,787	65,710
Actual return on plan assets	12,644	4,788
Employer contributions	3,000	8,500
Benefits paid	(3,936)	(3,072)
Administrative expenses	(131)	(139)
Fair value of plan assets at end of period	87,364	75,787	65,710
Funded (unfunded) status at end of period	6,641	2,836
Non-Qualified Retirement Plans [Member]
Change in Benefit Obligation:
Benefit obligation at beginning of period	13,154	13,015
Service cost	129	122	78
Interest cost	428	432	490
Actuarial loss	2,275	374
Benefits paid	(783)	(789)
Administrative expenses	0	0
Benefit obligation at end of period	15,203	13,154	13,015
Change in Plan Assets:
Fair value of plan assets at beginning of period	0	0
Actual return on plan assets	0	0
Employer contributions	783	789
Benefits paid	(783)	(789)
Administrative expenses	0	0
Fair value of plan assets at end of period	0	0	$ 0
Funded (unfunded) status at end of period	$ (15,203)	$ (13,154)