Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment
Gross property, plant and equipment	$ 1,803,926	$ 1,848,518
Less: Accumulated depreciation	(1,343,428)	(1,368,771)
Property, plant and equipment, net	460,498	479,747
Land
Property, Plant and Equipment
Gross property, plant and equipment	10,874	10,840
Land improvements
Property, Plant and Equipment
Gross property, plant and equipment	15,874	14,996
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	192,011	198,582
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	1,554,559	1,599,713
Construction in progress
Property, Plant and Equipment
Gross property, plant and equipment	$ 30,608	$ 24,387