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Weighted-Average Grant Date Fair Value of Options Granted and Weighted-Average Assumptions Used for Grants (Detail) (USD $)
9 Months Ended
Feb. 29, 2012
Stock-Based Compensation Plans  
Weighted average grant date fair value $ 13.80
Stock Options
 
Stock-Based Compensation Plans  
Expected volatility 0.450
Expected option term in years 6 years 8 months 12 days
Risk-free interest rate 1.31%
Expected dividend yield 0.02%