Other Comprehensive Loss - After-tax Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 126,651	$ 86,400	$ 115,038	$ 74,742	$ 74,742
Net current period change			338	(3,834)
Derivative Instrument	(17)	0	322	0
Amortization of actuarial losses			1,089	(932)
Ending balance	136,502	94,541	136,502	94,541	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			338	(3,834)
Derivative Instrument			0	0
Amortization of actuarial losses			0	0
Ending balance	(22,509)	(21,006)	(22,509)	(21,006)	(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			322	0
Amortization of actuarial losses			0	0
Ending balance	818	0	818	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			1,089	(932)
Ending balance	(24,031)	(24,995)	(24,031)	(24,995)	(25,120)
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(47,677)	(40,103)	(47,471)	(41,235)	(41,235)
Ending balance	$ (45,722)	$ (46,001)	$ (45,722)	$ (46,001)	$ (47,471)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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