Accumulated Other Comprehensive Loss - Reclassifications Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Amortization of pension and postretirement benefits items:
Prior service benefit/cost	$ (6)	$ (6)
Amortization of actuarial loss	88	135
Total before tax	82	129
Income tax benefit	(21)	(46)
Amount reclassified out of accumulated other comprehensive loss	$ 61	$ 83