Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment
Gross property, plant and equipment	$ 2,316,964	$ 2,278,614
Less: Accumulated depreciation	(1,593,945)	(1,567,268)
Property, plant and equipment, net	723,019	711,346
Land
Property, Plant and Equipment
Gross property, plant and equipment	16,431	16,652
Land improvements
Property, Plant and Equipment
Gross property, plant and equipment	13,758	13,615
Buildings and improvements
Property, Plant and Equipment
Gross property, plant and equipment	213,409	192,346
Machinery and equipment
Property, Plant and Equipment
Gross property, plant and equipment	1,996,779	1,969,493
Uncompleted construction
Property, Plant and Equipment
Gross property, plant and equipment	$ 76,587	$ 86,508