Other Comprehensive Loss - After-tax Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 136,502	$ 94,541	$ 115,038	$ 74,742	$ 74,742
Net current period change			(3,048)	(5,363)
Derivative Instrument	(515)	0	(193)	0
Amortization of actuarial losses			(1,008)	(1,992)
Ending balance	139,745	105,315	139,745	105,315	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			(3,048)	(5,363)
Derivative Instrument			0	0
Amortization of actuarial losses			0	0
Ending balance	(25,895)	(22,535)	(25,895)	(22,535)	(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			(193)	0
Amortization of actuarial losses			0	0
Ending balance	303	0	303	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			(1,008)	(1,992)
Ending balance	(26,128)	(26,055)	(26,128)	(26,055)	(25,120)
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(45,722)	(46,001)	(47,471)	(41,235)	(41,235)
Ending balance	$ (51,720)	$ (48,590)	$ (51,720)	$ (48,590)	$ (47,471)