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Income Taxes (Details)
3 Months Ended 6 Months Ended
Jul. 31, 2011
Jul. 31, 2010
Jul. 31, 2011
Jul. 31, 2010
Income Taxes        
Effective tax rate 27.00% 30.20% 26.80% 28.90%
Federal statutory rate 35.00% 35.00% 35.00% 35.00%