Comprehensive Income and Accumulated Other Comprehensive Income (Loss) - Summary of Effects of Reclassifications from Accumulated Other Comprehensive Income (Loss) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Pension and Other Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total net of tax	$ (1,409)
Reclassification out of Accumulated Other Comprehensive Income | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	2,350
Reclassification out of Accumulated Other Comprehensive Income | Prior service credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(59)
Reclassification out of Accumulated Other Comprehensive Income | Pension and Other Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	2,291
Tax benefit	(882)
Total net of tax	$ 1,409