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Fair Value of Stock Options Granted, Estimated using Weighted-Average Assumptions (Detail)
3 Months Ended 12 Months Ended
Aug. 31, 2013
May 31, 2013
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]    
Risk-free interest rate 0.80% 1.20%
Expected dividend yield 0.00% 0.00%
Expected stock price volatility 33.10% 39.20%
Expected option life (in years) 4 years 4 years