Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment
Gross property, plant and equipment	$ 1,943,663	$ 1,916,469
Less: Accumulated depreciation	(1,387,877)	(1,352,434)
Property, plant and equipment, net	555,786	564,035
Land
Property, Plant and Equipment
Gross property, plant and equipment	11,205	10,932
Land improvements
Property, Plant and Equipment
Gross property, plant and equipment	15,314	15,277
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	191,286	191,356
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	1,688,499	1,661,914
Uncompleted construction
Property, Plant and Equipment
Gross property, plant and equipment	$ 37,359	$ 36,990