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Other Postretirement Benefits - Schedule of Expected Benefit Payments (Details) - Other Postretirement Benefit Plans [Member]
$ in Thousands
Dec. 31, 2017
USD ($)
Other Postretirement Benefits  
2018 $ 5,968
2019 5,589
2020 5,286
2021 4,988
2022 4,655
2023-2027 $ 19,045