Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Property, plant and equipment
Less: Accumulated depreciation	$ (203,950)		$ (200,734)
Property, plant and equipment, net	90,685		88,247
Depreciation	3,763	$ 3,172
Land
Property, plant and equipment
Property, plant and equipment gross	1,137		1,130
Buildings and improvements
Property, plant and equipment
Property, plant and equipment gross	64,457		64,201
Machinery and equipment
Property, plant and equipment
Property, plant and equipment gross	$ 229,041		$ 223,650