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Share Repurchase Plan - Additional Information (Detail) (USD $)
1 Months Ended 3 Months Ended
Dec. 13, 2011
Nov. 30, 2012
Nov. 30, 2011
Schedule Of Share Repurchase Programs [Line Items]      
Share buy-back, amount authorized $ 50,000,000    
Share buy-back plan, number of shares repurchased   634,170  
Total cost of repurchased shares   $ 8,091,000 $ 18,601,000