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Equity Incentive Plans - Additional Information (Details)
1 Months Ended 3 Months Ended
Mar. 16, 2016
Aug. 31, 2015
USD ($)
period
shares
Apr. 30, 2018
USD ($)
plan
shares
Apr. 30, 2017
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of equity incentive plans | plan     2  
Total stock-based compensation expense     $ 43,955,000 $ 32,219,000
Compensation cost, weighted average term     2 years 2 months 12 days  
2015 Equity Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Equity awards of vest expire period (no later than)     10 years  
2015 Equity Incentive Plan | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Purchase price as percentage of fair market value of common stock     100.00%  
Equity awards of vest period     2 years  
2015 Equity Incentive Plan | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Equity awards of vest period     4 years  
2015 Equity Incentive Plan | Class A        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares initially reserved for issuance (in shares) | shares     27,000,000  
Increase in shares reserved by percentage of capital stock     5.00%  
2015 Employee Stock Purchase Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Employee stock purchase plan offering period 24 months      
Number of purchase periods | period   4    
Purchase period, term   6 months    
Total stock-based compensation expense     $ 6,700,000 4,100,000
Unrecognized stock-based compensation expense     $ 32,600,000  
Compensation cost, weighted average term     1 year 1 month 6 days  
2015 Employee Stock Purchase Plan | Class A        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Increase in shares reserved by percentage of capital stock   1.00%    
Purchase price as percentage of fair market value of common stock   85.00%    
Shares reserved for future issuance (in shares) | shares   3,500,000    
Payroll deductions percentage   30.00%    
Share cap for ESPP at purchase date (in shares) | shares   3,000    
Calendar year gap for ESPP contribution amount   $ 25,000    
Modification charges       $ 9,000,000