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Stock-Based Compensation - Schedule of Assumptions Used to Determine Grant Date Fair Value of Market Based Restricted Common Shares (Detail) - Market-Based Restricted Common Shares
12 Months Ended
May 31, 2015
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%