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Stock-based Compensation Expense Assumption Used to Estimate the Fair Value of Stock-Based Awards (Details)
3 Months Ended
Apr. 30, 2014
Apr. 30, 2013
ESP Plan
   
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]    
Expected dividends 0.00% 0.00%
Expected forfeitures 7.20% 7.70%
ESP Plan | Minimum
   
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]    
Range of expected volatilities 30.00% 27.00%
Range of expected lives (in years) 6 months 6 months
Range of risk-free interest rates 0.10% 0.10%
ESP Plan | Maximum
   
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]    
Range of expected volatilities 33.00% 36.00%
Range of expected lives (in years) 2 years 2 years
Range of risk-free interest rates 0.40% 0.30%
Performance Stock Unit
   
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]    
Range of expected volatilities 30.00% 34.00%
Expected dividends 0.00% 0.00%
Range of risk-free interest rates 0.10%  
Expected forfeitures 7.20% 7.70%
Performance Stock Unit | Minimum
   
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]    
Range of risk-free interest rates   0.10%
Performance Stock Unit | Maximum
   
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]    
Range of risk-free interest rates   0.10%