Employee Benefit Plans (Schedule of Amounts Recognized in Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Change In Benefit Obligation [Line Items]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	$ 40,058	$ 46,119
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Prior Service Costs (Credit) Arising During Period, Net of Tax	804	703
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	40,862	46,822
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Change In Benefit Obligation [Line Items]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	35,672	32,156
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Prior Service Costs (Credit) Arising During Period, Net of Tax	(11,806)	(13,121)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	$ 23,866	$ 19,035