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Summary of Transactions Involving Stock Units and Director Stock Grants (Detail) (Stock And Stock Units, USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended
Aug. 31, 2013
Aug. 31, 2012
Stock And Stock Units
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Performance awards, beginning of year, No. of Performance Awards 329 342
Granted, No. of Stock Units 7  
Vested and settled, No. of Stock Units   (3)
Cancelled, No. of Stock Units (7) (6)
Performance awards, end of year, No. of Performance Awards 329 333
Performance awards, beginning of year, Weighted Average Fair Value $ 26.07 $ 21.73
Granted, Weighted Average Fair Value $ 38.88  
Vested and settled, Weighted Average Fair Value   $ 21.32
Cancelled, Weighted Average Fair Value $ 25.50 $ 21.25
Performance awards, end of year, Weighted Average Fair Value $ 26.36 $ 21.74