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Stock-Based Compensation - Assumptions Used to Estimate Fair Value of Employee Stock Purchase Plan Using Black-Scholes Option Pricing Model (Details) - ESPP
3 Months Ended 6 Months Ended
Jul. 31, 2017
Jul. 31, 2016
Jul. 31, 2017
Jul. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected volatility, minimum 35.00% 44.00% 35.00% 44.00%
Risk-free interest rate, minimum 0.90% 0.50% 0.90% 0.50%
Expected volatility, maximum 41.00% 50.00% 41.00% 50.00%
Risk-free interest rate, maximum 1.30% 1.00% 1.30% 1.00%
Minimum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected term (in years) 6 months 6 months 6 months 6 months
Maximum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected term (in years) 2 years 2 years 2 years 2 years