Employee and Retiree Benefit Plans (Benefit Payments, Reflected Expected Future Service as Appropriate which are Expected to be Paid in Future Years from Assets of Plans or by Company) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2018	$ 39,929
2019	40,236
2020	41,220
2021	42,276
2022	43,554
2023-2027	227,039
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2018	6,259
2019	6,280
2020	6,357
2021	6,489
2022	6,560
2023-2027	$ 33,971

Employee and Retiree Benefit Plans (Benefit Payments, Reflected Expected Future Service as Appropriate which are Expected to be Paid in Future Years from Assets of Plans or by Company) (Details)
$ in Thousands

Dec. 31, 2017

USD ($)

Defined Benefit Plan Disclosure [Line Items]

$ 39,929

40,236

41,220

42,276

43,554

227,039