Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 544,880	$ 531,832
Less: accumulated depreciation	(386,833)	(373,892)
Net property, plant and equipment	158,047	157,940
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,047	3,188
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	119,819	117,910
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	393,327	386,690
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 28,687	$ 24,044