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Share Repurchase Plan - Additional Information (Detail) (USD $)
1 Months Ended 6 Months Ended 15 Months Ended
Dec. 13, 2011
Feb. 28, 2013
Feb. 29, 2012
Feb. 28, 2013
Equity, Class of Treasury Stock [Line Items]        
Share buy-back plan, amount authorized $ 50,000,000      
Share buy-back plan, number of shares repurchased       715,859
Total cost of repurchased shares   $ 12,414,000 $ 22,685,000 $ 33,700,000