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Stock-Based Compensation - Additional Information (Detail)
3 Months Ended
Aug. 31, 2015
USD ($)
$ / shares
shares
Non-Qualified Stock Options  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Non-qualified stock options, granted | shares 153,500
Non-qualified stock option, per share price $ 30.92
Non-qualified stock option, fair value, per share price $ 9.55
Pre-tax stock-based compensation | $ $ 1,305,000
Pre-tax stock-based compensation, period of recognition 3 years
Service-Based Restricted Common Shares  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Pre-tax stock-based compensation, period of recognition 3 years
Performance share awards granted | shares 148,850
Restricted common shares, fair value per share $ 30.92
Pre-tax stock-based compensation | $ $ 4,096,000
Performance Shares  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Pre-tax stock-based compensation, period of recognition 3 years
Performance share awards granted | shares 94,700
Pre-tax stock-based compensation | $ $ 2,852,000