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Inventories (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Principally average cost:    
Raw material and supplies $ 42,751 $ 42,969
Work in process 203,179 179,445
Finished goods 51,094 57,645
Gross inventories 297,024 280,059
Excess of average cost over LIFO inventory value 90,899 92,883
Net inventories $ 206,125 $ 187,176