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Stock Purchase - Additional Information (Detail) - shares
12 Months Ended
May 31, 2017
May 31, 2016
Aug. 31, 2016
Dec. 31, 2008
Stock Repurchase Program [Line Items]        
Shares authorized to purchase       1,125,000
Number of shares available to be repurchased     1,012,974  
Number of shares repurchased   0    
During fiscal 2017        
Stock Repurchase Program [Line Items]        
Number of shares repurchased 0