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Pension and Postretirement Plans (Assumed Health Care Cost Trend Rates) (Details 12) - Other Postretirement Benefits Plan [Member]
$ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Benefit obligation at end of year, 1% Increase $ 1,304
Benefit obligation at end of year, 1% Decrease (1,194)
Service cost plus interest cost, 1% Increase 177
Service cost plus interest cost, 1% Decrease $ (158)