Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment
Gross property, plant and equipment	$ 1,894,805	$ 1,848,518
Less: Accumulated depreciation	(1,411,968)	(1,368,771)
Property, plant and equipment, net	482,837	479,747
Land
Property, Plant and Equipment
Gross property, plant and equipment	10,828	10,840
Land improvements
Property, Plant and Equipment
Gross property, plant and equipment	14,866	14,996
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	202,273	198,582
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	1,643,743	1,599,713
Construction in progress
Property, Plant and Equipment
Gross property, plant and equipment	$ 23,095	$ 24,387