Employee and Retiree Benefit Plans (Amounts Included in Accumulated Other Comprehensive Income Expected to be Amortized into Net Periodic Benefit Expense) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ (15,890)
Prior service (cost) credit	(1,021)
Amounts included in accumulated other comprehensive loss expected to be amortized into net periodic benefit expense	(16,911)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	38
Amounts included in accumulated other comprehensive loss expected to be amortized into net periodic benefit expense	$ 38