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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 - Class B Common Stock
3 Months Ended
Aug. 31, 2016
Aug. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 1.10% 1.00%
Expected volatility 17.30% 23.60%
Weighted average expected life 6 years 5 years 9 months 18 days
Risk-free interest rate 1.30% 1.70%