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Fair Value Measurements - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2012
Dec. 31, 2011
Commodity Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Expected unrealized gain to be reclassified into earnings $ 0.1  
Unrealized gain on commodity hedges   $ 0.2