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Shareholder's Equity - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
1 Months Ended 6 Months Ended
Aug. 25, 2011
Program
Jul. 31, 2011
Jul. 31, 2012
Feb. 28, 2006
Stockholders Equity Note [Line Items]        
Common shares authorized for repurchase, shares 20,000,000     8,000,000
Number of stock repurchase authorizations program 2      
Stock repurchased and retired during period, common shares   7,165,199    
Stock repurchased and retired during period, value   $ 215,993    
Average cost per share   $ 30.14    
Additional paid-in-capital   0 10,581  
Retained earnings reduction related to shares repurchased   $ 179,543