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Equity Compensation Plans - Additional Information (Detail) (USD $)
3 Months Ended 12 Months Ended
Aug. 31, 2013
Aug. 31, 2012
May 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share based compensation $ 789,000 $ 682,000  
Weighted-Average Grant-Date Fair Value of Options Granted $ 14.65   $ 13.81
Employee Stock Purchase Plan | 2011 Employee Stock Purchase Plan
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Annual maximum limit percentage of compensation to purchase shares 5.00%    
Minimum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock option vesting period 5 years    
Maximum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock option vesting period