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Summarized Information about Options Outstanding (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Outstanding Options 90,250
Exercisable Options 90,250
Price Range $21 to $30
 
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Price Range, Lower Range $ 21
Price Range, Upper Range $ 30
Outstanding Options 68,750
Average Remaining Contract Life 1 year 1 month 6 days
Average Exercise Price $ 28.86
Average Aggregate Intrinsic Value $ 22.21
Exercisable Options 68,750
Average Exercise Price $ 28.86
Average Aggregate Intrinsic Value 22.21
Price Range $31 to $37
 
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Price Range, Lower Range $ 31
Price Range, Upper Range $ 37
Outstanding Options 21,500
Average Remaining Contract Life 2 years 2 months 12 days
Average Exercise Price $ 33.39
Average Aggregate Intrinsic Value 17.68
Exercisable Options 21,500
Average Exercise Price $ 33.39
Average Aggregate Intrinsic Value $ 17.68