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Income Taxes (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Apr. 30, 2012
Apr. 30, 2011
Income Taxes [Abstract]    
Effective tax rate 29.90% 26.60%
Federal statutory rate 35.00%  
Increase in provision for income taxes, percentage 30.00%  
Provision for income taxes $ 23.0 $ 17.7