Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Property, plant and equipment
Less: Accumulated depreciation	$ (202,765)		$ (197,038)
Property, plant and equipment, net	85,174		82,111
Depreciation	6,524	$ 6,308
Land
Property, plant and equipment
Property, plant and equipment gross	2,635		2,330
Buildings and improvements
Property, plant and equipment
Property, plant and equipment gross	64,309		63,621
Machinery and equipment
Property, plant and equipment
Property, plant and equipment gross	$ 220,995		$ 213,198