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SHARE-BASED AWARDS AND OPTIONS - Valuation Assumptions (Details) - Employee stock option
3 Months Ended
Aug. 31, 2016
Aug. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 1.05% 1.62%
Expected volatility 31.58% 28.65%
Dividend yield 0.06% 0.10%
Expected term (years) 5 years 5 years