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Shareholder's Equity (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
0 Months Ended 3 Months Ended
Aug. 25, 2011
item
Nov. 16, 2010
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Apr. 30, 2011
Apr. 30, 2012
Jan. 31, 2012
Feb. 28, 2006
Shareholders' Equity [Abstract]            
Common shares authorized for repurchase, shares 20,000,000 20,000,000       8,000,000
Number of stock repurchase authorizations program 2 2        
Stock repurchased and retired during period, common shares     4,824,869      
Stock repurchased and retired during period, value     $ 148,674      
Average cost per share     $ 30.81      
Additional paid-in-capital        5,971     
Retained earnings reduction related to shares repurchased     $ 115,778