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Dividend Program (Detail) - USD ($)
$ / shares in Units, $ in Thousands
6 Months Ended
Nov. 30, 2017
Oct. 29, 2017
Oct. 30, 2016
Dividends [Line Items]      
Cash dividends paid   $ 4,603 $ 4,307
Special Dividend [Member]      
Dividends [Line Items]      
Cash dividends paid   $ 2,600 $ 2,500
Cash dividend payment, per share   $ 0.21 $ 0.21
Quarterly Dividend [Member]      
Dividends [Line Items]      
Cash dividend declared, per share   $ 0.08  
Cash dividends paid   $ 2,000 $ 1,800
Cash dividend payment, per share   $ 0.08 $ 0.07
Subsequent Event [Member] | Quarterly Dividend [Member]      
Dividends [Line Items]      
Increase in cash dividend, percentage 12.50%    
Cash dividend declared, per share $ 0.09    
Date of payment to shareholders entitled to dividends Jan. 16, 2018    
Date of record of shareholders entitled to dividends Jan. 02, 2018