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Stockholders' Equity - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Apr. 30, 2019
Jan. 31, 2019
Jan. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Stock options, granted 1,314,375    
Unrecognized compensation cost related to unvested stock options granted $ 163.6    
Intrinsic value of options exercised $ 60.8    
CEO [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Stock options, granted     2,838,635
2013 Equity Incentive Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Weighted-average grant date fair value of options granted $ 58.29    
Stock options, granted 1,314,375    
Maximum [Member] | 2012 and 2013 Equity Incentive Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Share-based compensation cost recognition vesting service period 9 years    
Minimum [Member] | 2012 and 2013 Equity Incentive Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Share-based compensation cost recognition vesting service period 4 years    
Restricted Stock Units (RSUs) [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Award vesting period   4 years  
Weighted average period of unvested stock 2 years 1 month 6 days    
Weighted average grant date fair value, RSUs granted $ 131.26    
Number of shares, RSUs granted 193,773    
Unrecognized compensation cost related to unvested RSUs $ 126.4    
Total intrinsic value, vested $ 37.7    
Restricted Stock Units (RSUs) [Member] | 2013 Equity Incentive Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Weighted average grant date fair value, RSUs granted $ 131.26    
Number of shares, RSUs granted 193,773    
Restricted Stock Units (RSUs) [Member] | Maximum [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Award vesting period 1 year    
Stock Options [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Award vesting period 4 years    
Weighted average period of unvested stock 3 years 10 months 24 days    
Stock Options [Member] | CEO [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Number of vesting tranches based on market conditions     The stock option award is made up of five separate tranches. The first tranche vests over time, while the remaining four tranches vest based on certain stock price targets (market conditions).