Other Comprehensive Loss - After-tax Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 74,742
Net current period change	1,470	$ 1,822
Amortization of actuarial losses	(338)	(740)
Ending balance	86,400
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(17,172)	(24,313)
Net current period change	1,470	1,822
Ending balance	(15,702)	(22,491)
Pension and post-retirement benefits plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(24,063)	(24,532)
Net current period change	0	0
Amortization of actuarial losses	(338)	(740)
Ending balance	(24,401)	(25,272)
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(41,235)	(48,845)
Ending balance	$ (40,103)	$ (47,763)