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Common Stock and Stock-Based Compensation - Weighted Average Assumptions Used to Estimate Fair Values (Detail) - Employee Stock Option - Stock Incentive Plan 1990 - Class B Common Stock
3 Months Ended
Aug. 31, 2015
Aug. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 1.00% 1.20%
Expected volatility 23.60% 23.60%
Weighted average expected life (in years) 5 years 9 months 5 years 9 months 18 days
Risk-free interest rate 1.70% 1.70%