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Equity Incentive Plan - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Nov. 30, 2015
Nov. 30, 2014
Nov. 30, 2015
Nov. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected period to recognize the unrecognized share based compensation cost     3 years  
Selling, general and administrative expenses        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Allocated share based compensation $ 375 $ 361 $ 648 $ 649
Restricted Stock Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock units granted (in shares) 78,000 18,000 182,000 87,000
Unrecognized share based compensation cost $ 2,488   $ 2,488  
Expected period to recognize the unrecognized share based compensation cost     2 years 2 months 6 days  
Vested restricted stock units 315,000 397,000 315,000 397,000
Exercise of conversion right, period     5 years  
Total excess tax benefit (shortfall) realized     $ 15 $ 116
2005 Equity Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Maximum number of shares authorized 1,000,000   1,000,000