Employee and Retiree Benefit Plans (Amounts Included in Accumulated Other Comprehensive Income Not Recognized in Net Periodic Benefit Expense) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ (269,063)
Prior service (cost) credit	(5,824)
Amounts included in accumulated other comprehensive loss which have not been recognized in net periodic benefit expense	(274,887)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	221
Prior service (cost) credit	38
Amounts included in accumulated other comprehensive loss which have not been recognized in net periodic benefit expense	$ 259