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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, 2016
Apr. 30, 2015
Performance Stock Unit    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Range of expected volatilities   27.30%
Expected dividends 0.00% 0.00%
Range of risk-free interest rates   0.20%
Performance Stock Unit | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Range of expected volatilities 38.40%  
Range of risk-free interest rates 0.60%  
Performance Stock Unit | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Range of expected volatilities 38.60%  
Range of risk-free interest rates 0.70%  
Employee Qualified Stock Purchase Plan 1998 ESP Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected dividends 0.00% 0.00%
Employee Qualified Stock Purchase Plan 1998 ESP Plan | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Range of expected volatilities 35.00% 27.70%
Range of expected lives (in years) 6 months 6 months
Range of risk-free interest rates 0.50% 0.10%
Employee Qualified Stock Purchase Plan 1998 ESP Plan | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Range of expected volatilities 40.20% 28.20%
Range of expected lives (in years) 2 years 2 years
Range of risk-free interest rates 0.90% 0.60%