Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment
Gross property, plant and equipment	$ 2,106,991	$ 2,186,407
Less: Accumulated depreciation	(1,480,375)	(1,523,163)
Property, plant and equipment, net	626,616	663,244
Land
Property, Plant and Equipment
Gross property, plant and equipment	13,742	15,721
Land improvements
Property, Plant and Equipment
Gross property, plant and equipment	15,751	15,898
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	208,164	205,409
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	1,804,315	1,861,965
Uncompleted construction
Property, Plant and Equipment
Gross property, plant and equipment	$ 65,019	$ 87,414