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Derivative Financial Instruments and Fair Value and Credit Risk of Financial Instruments - Additional information (Detail) (USD $)
In Millions, unless otherwise specified
6 Months Ended 12 Months Ended
Dec. 31, 2010
Dec. 31, 2011
Jun. 30, 2010
Derivative [Line Items]      
Unrealized gain, included in Accumulated other comprehensive income/loss   $ 0.5  
Percentage of assets classified within level 3 of fair value hierarchy to total assets and liabilities measured at fair value   1.00%  
Commodity Contract
     
Derivative [Line Items]      
LME copper prices, average (per ton) 7,828 8,836 6,651
LME copper prices, average provisional price (per ton)   8,160  
Applicable forward copper price   7,643  
Commodity Contract | Sales
     
Derivative [Line Items]      
Gain (loss) on mark-to-market value of contracts   $ (20.6)