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Pension and Postretirement Plans (Future Estimated Benefit Payments) (Details 4)
$ in Thousands
Dec. 31, 2017
USD ($)
Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
2018 $ 73,418
2019 74,433
2020 74,572
2021 75,661
2022 73,921
2023-2027 371,073
Supplemental Executive Retirement Plan (SERP) [Member]  
Defined Benefit Plan Disclosure [Line Items]  
2018 5,943
2019 6,320
2020 6,454
2021 6,591
2022 6,719
2023-2027 34,165
Other Postretirement Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
2018 1,920
2019 1,885
2020 2,054
2021 2,086
2022 2,153
2023-2027 $ 10,178