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Property, Plant and Equipment (Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Jun. 30, 2017
Property, Plant and Equipment [Line Items]
Depreciation				$ 33,500	$ 29,300	$ 26,600
Impairment charges				1,506	807	0
Assets held for sale				0	896
Gain on sale of property, plant and equipment				$ 3,087	$ 5,329	$ 0
Property plant and equipment, held for sale							$ 400
Arizona
Property, Plant and Equipment [Line Items]
Assets held for sale								$ 900
Gain on sale of property, plant and equipment	$ 400
Belgium
Property, Plant and Equipment [Line Items]
Gain on sale of property, plant and equipment		$ 4,400	$ 900