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One Percentage Point Change in Health Care Cost Trend Rates (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]  
Effect of 1% increase on total service and interest cost components $ 764
Effect of 1% increase on postretirement employee benefit obligation 12,841
Effect of 1% decrease on total service and interest cost components (646)
Effect of 1% decrease on postretirement employee benefit obligation $ (11,043)