Annual report pursuant to Section 13 and 15(d)

Employee Retirement Plans - Changes in Healthcare Cost Trend Rate (Details)

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Employee Retirement Plans - Changes in Healthcare Cost Trend Rate (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
Pension plan  
Amounts included in other comprehensive loss, net of tax  
Net actuarial gain (loss) $ (6,636)
Amounts that will be amortized from accumulated other comprehensive income loss into net periodic pension or OPEB cost in the next fiscal year  
Estimated actuarial gain (loss) (706)
Other postretirement benefit cost  
Effect of one percentage point change in the healthcare cost trend rate  
Effect on total service and interest cost, 1% increase 54
Effect on total service and interest cost, 1% decrease (46)
Effect on postretirement benefit obligation, 1% increase 762
Effect on postretirement benefit obligation, 1% decrease (669)
Amounts included in other comprehensive loss, net of tax  
Net actuarial gain (loss) 1,392
Amounts that will be amortized from accumulated other comprehensive income loss into net periodic pension or OPEB cost in the next fiscal year  
Estimated actuarial gain (loss) $ 211