Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Property, Plant and Equipment
Gross property, plant and equipment	$ 2,337,488	$ 2,278,614
Less: Accumulated depreciation	(1,628,877)	(1,567,268)
Property, plant and equipment, net	708,611	711,346
Land
Property, Plant and Equipment
Gross property, plant and equipment	18,796	16,652
Land improvements
Property, Plant and Equipment
Gross property, plant and equipment	14,245	13,615
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	214,169	192,346
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	2,003,319	1,969,493
Uncompleted construction
Property, Plant and Equipment
Gross property, plant and equipment	$ 86,959	$ 86,508