Pension and Other Postretirement Benefits (Details 10) $ in Thousands	Dec. 31, 2017 USD ($)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	$ 4,600
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2018	29,261
2019	29,243
2020	29,086
2021	29,205
2022	29,378
Years 2023-2027	144,074
Total	290,247
Other postretirement benefit plans [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2018	3,653
2019	3,485
2020	3,204
2021	3,014
2022	2,848
Years 2023-2027	11,722
Total	$ 27,926