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	$ 11,189
2019	11,812
2020	12,361
2021	11,842
2022	11,640
2023-2027	58,627
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Gross Projected Benefit Payments [Abstract]
2018	1,352
2019	1,329
2020	1,298
2021	1,254
2022	1,215
2023-2027	5,111
Expected Medicare Part D Subsidies [Abstract]
2018	5
2019	4
2020	3
2021	3
2022	3
2023-2027	14
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
2018	1,347
2019	1,325
2020	1,295
2021	1,251
2022	1,212
2023-2027	$ 5,097