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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, 2017
Apr. 30, 2016
Performance Stock Unit    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Range of expected volatilities 31.80%  
Expected dividends 0.00% 0.00%
Range of risk-free interest rates 1.00%  
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 31.40% 35.00%
Range of expected lives (in years) 6 months 6 months
Range of risk-free interest rates 0.90% 0.50%
Employee Qualified Stock Purchase Plan 1998 ESP Plan | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Range of expected volatilities 33.70% 40.20%
Range of expected lives (in years) 2 years 2 years
Range of risk-free interest rates 1.30% 0.90%