Property, Plant and Equipment - PPE (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 636,672	$ 560,781
Accumulated depreciation	(392,344)	(347,219)
Property, plant and equipment, net	244,328	213,562
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	13,607	13,557
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	105,036	99,233
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 518,029	$ 447,991