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Assumptions To Value Stock Options (Detail)
12 Months Ended
May 31, 2016
May 31, 2015
May 31, 2014
Non-Qualified Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 2.33% 1.88% 2.28%
Expected volatility 38.40% 50.92% 52.23%
Risk-free interest rate 1.98% 1.88% 1.69%
Expected life (years) 6 years 6 years 6 years
Market-Based Restricted Common Shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield   1.60%  
Expected volatility   44.00%  
Risk-free interest rate   1.70%