Comprehensive Income and Accumulated Other Comprehensive Income (Loss) - Summary of Effects of Reclassifications from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Settlement loss
Amortization of pension and other postretirement benefit plan items:
Total before tax	$ 1,342
Pension and Other Postretirement Benefit Plans
Amortization of pension and other postretirement benefit plan items:
Total net of tax	(3,123)	$ (1,567)
Amount Reclassified from Accumulated Other Comprehensive Income | Actuarial losses
Amortization of pension and other postretirement benefit plan items:
Total before tax	2,798
Amount Reclassified from Accumulated Other Comprehensive Income | Prior service credit
Amortization of pension and other postretirement benefit plan items:
Total before tax	(42)
Amount Reclassified from Accumulated Other Comprehensive Income | Pension and Other Postretirement Benefit Plans
Amortization of pension and other postretirement benefit plan items:
Total before tax	4,098
Tax benefit	(975)
Total net of tax	$ 3,123