Benefit Plans and Other Postretirement Benefits, Projected Benefit Payments (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Pension Plan [Member]
Defined Benefit Plan, Gross Projected Benefit Payments [Abstract]
2018	$ 30,475
2019	28,755
2020	29,621
2021	29,721
2022	30,712
2023-2027	155,784
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Gross Projected Benefit Payments [Abstract]
2018	3,277
2019	3,189
2020	3,229
2021	3,351
2022	3,384
2023-2027	14,773
Expected Medicare Part D Subsidies [Abstract]
2018	22
2019	19
2020	21
2021	25
2022	30
2023-2027	141
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
2018	3,255
2019	3,170
2020	3,208
2021	3,326
2022	3,354
2023-2027	$ 14,632