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Derivatives and Financial Instruments (Narrative) (Detail)
0 Months Ended 9 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2012
Derivative [Line Items]      
Percentage of derivative contract volume expiring within next 12 months 99.00% 99.00%  
Payment terms of receivables     30 days or less