Employee Benefit Plans (Schedule of Changes in Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Fair Value of Plan Assets, Beginning Balance	$ 84,770
Defined Benefit Plan, Fair Value of Plan Assets, Ending Balance	103,236	$ 84,770
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(68,907)	(77,185)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Fair Value of Plan Assets, Beginning Balance	84,770	68,435
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	14,481	6,584
Defined Benefit Plan, Plan Assets, Contributions by Employer	22,866	15,950
Defined Benefit Plan, Contributions by Plan Participants (Deprecated 2017-01-31)	0	0
Defined Benefit Plan, Plan Assets, Payment for Settlement	(12,907)	(3,152)
Defined Benefit Plan, Benefits Paid (Deprecated 2017-01-31)	(5,974)	(3,047)
Defined Benefit Plan, Fair Value of Plan Assets, Ending Balance	103,236	84,770
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(68,907)	(77,185)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Fair Value of Plan Assets, Beginning Balance	0	0
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	0	0
Defined Benefit Plan, Plan Assets, Contributions by Employer	497	410
Defined Benefit Plan, Contributions by Plan Participants (Deprecated 2017-01-31)	354	305
Defined Benefit Plan, Plan Assets, Payment for Settlement	0	0
Defined Benefit Plan, Benefits Paid (Deprecated 2017-01-31)	(851)	(715)
Defined Benefit Plan, Fair Value of Plan Assets, Ending Balance	0	0
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ (70,198)	$ (60,524)