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Common Stock - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
May 31, 2018
May 31, 2017
May 31, 2016
Shareholder Rights [Line Items]      
Authorization of stock repurchase program Jan. 08, 2008    
Shares repurchased 0 0 800,000
Shares repurchased, value     $ 35,098
Repurchase of common stock price per shares     $ 43.88
Minimum      
Shareholder Rights [Line Items]      
Shares authorized to be repurchased, per year 1,000,000 1,000,000 1,000,000
Maximum      
Shareholder Rights [Line Items]      
Shares authorized to be repurchased, per year 2,000,000 2,000,000 2,000,000