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Stock-based Compensation Expense Assumption Used to Estimate the Fair Value of Stock-Based Awards (Details)
3 Months Ended 6 Months Ended
Jul. 31, 2016
Jul. 31, 2015
Jul. 31, 2016
Jul. 31, 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%