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Derivative Financial Instruments (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Jun. 30, 2012
Jun. 30, 2012
Aluminum Futures Contracts [Member]
Dec. 31, 2011
Aluminum Futures Contracts [Member]
Derivative [Line Items]      
Notional amount that hedged future purchases of aluminum to meet fixed-price forward sales contract obligations   $ 8.9 $ 10.8
Weight of aluminum that hedged future purchase of aluminum to meet fixed - price forward sales contract obligations, lbs   9,100,000 11,000,000
Amounts of unrealized after-tax losses on derivative instruments $ 0.6