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Accounting Standards and Significant Accounting Policies (Detail) - USD ($)
12 Months Ended
Jan. 31, 2019
Jan. 31, 2018
Jan. 31, 2017
Feb. 01, 2018
Sep. 30, 2017
Jun. 30, 2013
Accounting Policies [Line Items]            
Period to pay portion of total arrangement fee, days 30 days          
Current unearned revenue anticipated recognition term, months 12 months          
Advertising expense $ 51,000,000 $ 43,000,000 $ 35,000,000      
2018 Notes            
Accounting Policies [Line Items]            
Convertible senior notes, interest rate 0.75%         0.75%
Convertible Senior Notes, principal amount $ 0 350,000,000       $ 350,000,000.0
2020 Notes            
Accounting Policies [Line Items]            
Convertible senior notes, interest rate 1.50%         1.50%
Convertible Senior Notes, principal amount $ 249,975,000 250,000,000       $ 250,000,000.0
2022 Notes            
Accounting Policies [Line Items]            
Convertible senior notes, interest rate 0.25%       0.25%  
Convertible Senior Notes, principal amount $ 1,150,000,000 $ 1,150,000,000     $ 1,150,000,000.00  
Minimum            
Accounting Policies [Line Items]            
Subscriptions contract period, years 3 years          
Accounting Standards Update 2014-09            
Accounting Policies [Line Items]            
Amortization period, deferred commissions 5 years          
Accounting Standards Update 2016-16            
Accounting Policies [Line Items]            
Cumulative effect of new accounting principle       $ 400,000