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Stock-based Compensation Expense (Assumption Used to Estimate the Fair Value of Stock-Based Awards) (Details)
3 Months Ended 9 Months Ended
Oct. 31, 2020
Oct. 31, 2019
Oct. 31, 2020
Oct. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected dividends (in percentage)     0.00%  
Performance Stock Unit        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Range of expected volatilities (in percentage)     50.70% 36.30%
Expected dividends (in percentage)     0.00% 0.00%
Range of risk-free interest rates (in percentage)     0.30% 2.50%
1998 Employee Qualified Stock Purchase Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected dividends (in percentage) 0.00% 0.00% 0.00% 0.00%
Range of risk-free interest rates (in percentage) 10.00%      
1998 Employee Qualified Stock Purchase Plan | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Range of expected volatilities (in percentage) 41.50% 32.70% 39.40% 32.70%
Range of expected lives (in years) 6 months 6 months 6 months 6 months
Range of risk-free interest rates (in percentage)   1.70% 0.10% 1.70%
1998 Employee Qualified Stock Purchase Plan | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Range of expected volatilities (in percentage) 45.00% 35.90% 45.80% 39.70%
Range of expected lives (in years) 2 years 2 years 2 years 2 years
Range of risk-free interest rates (in percentage)   1.90% 0.50% 2.50%