Other Comprehensive Loss - After-tax Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 115,038	$ 74,742	$ 74,742
Net current period change	104	1,470
Derivative Instrument	339	0
Amortization of actuarial losses	(649)	(338)
Ending balance	126,651	86,400	115,038
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(22,847)	(17,172)	(17,172)
Net current period change	104	1,470
Derivative Instrument	0	0
Amortization of actuarial losses	0	0
Ending balance	(22,743)	(15,702)	(22,847)
Derivative instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	496	0	0
Net current period change	0	0
Derivative Instrument	339	0
Amortization of actuarial losses	0	0
Ending balance	835	0	496
Pension and post-retirement benefits plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(25,120)	(24,063)	(24,063)
Net current period change	0	0
Derivative Instrument	0	0
Amortization of actuarial losses	(649)	(338)
Ending balance	(25,769)	(24,401)	(25,120)
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(47,471)	(41,235)	(41,235)
Ending balance	$ (47,677)	$ (40,103)	$ (47,471)