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Convertible Senior Notes - Narrative (Details)
1 Months Ended 9 Months Ended
Apr. 30, 2018
USD ($)
shares
day
$ / shares
Oct. 31, 2019
USD ($)
$ / shares
Oct. 31, 2018
USD ($)
Apr. 04, 2018
$ / shares
Debt Instrument [Line Items]        
Proceeds from issuance of convertible senior notes, net of issuance costs   $ 0 $ 562,062,000  
Debt issuance costs, net of amortization $ 12,900,000      
Closing price of stock (in dollars per share) | $ / shares   $ 19.46    
Payment for purchase of capped calls   $ 0 $ 64,630,000  
Capped Call        
Debt Instrument [Line Items]        
Payment for purchase of capped calls 64,600,000      
Convertible Senior Notes        
Debt Instrument [Line Items]        
Debt issuance costs, net of amortization 9,800,000 7,088,000    
Additional Paid-In Capital        
Debt Instrument [Line Items]        
Debt issuance costs, net of amortization $ 3,100,000 $ 3,068,000    
Class A        
Debt Instrument [Line Items]        
Conversion price (in dollars per share) | $ / shares $ 26.27      
Closing price of stock (in dollars per share) | $ / shares   $ 19.46   $ 19.83
Class A | Capped Call        
Debt Instrument [Line Items]        
Exercise price (in dollars per share) | $ / shares $ 39.66      
Exercise price premium percentage over last reported sales price       100.00%
Convertible Senior Notes        
Debt Instrument [Line Items]        
Principal amount $ 575,000,000.0 $ 575,000,000.0    
Interest rate (as a percent) 0.125%      
Proceeds from issuance of convertible senior notes, net of issuance costs $ 562,100,000      
Conversion percentage of principal amount plus accrued and unpaid contingent interest 100.00%      
Convertible debt, fair value based on the closing trading price per $100 of the Notes   602,800,000    
If-converted value   $ 425,900,000    
Convertible Senior Notes | Class A        
Debt Instrument [Line Items]        
Number of convertible shares at initial conversion rate (in shares) | shares 21,884,155      
Conversion ratio (in shares) 0.0380594      
Conversion price (in dollars per share) | $ / shares $ 26.27      
Redemption percentage of principal amount of Notes to be redeemed 100.00%      
Convertible Senior Notes | Class A | Any Fiscal Quarter Commencing After the Fiscal Quarter Ending on July 31, 2018        
Debt Instrument [Line Items]        
Threshold trading days | day 20      
Threshold consecutive trading days | day 30      
Threshold percentage of stock price trigger 130.00%      
Convertible Senior Notes | Class A | Five Business Day Period After any Five Consecutive Trading Day Period        
Debt Instrument [Line Items]        
Threshold consecutive trading days | day 5      
Threshold percentage of stock price trigger 98.00%      
Threshold business days | day 5      
Convertible Senior Notes | Class A | Immediately Preceding the Date on Which We Provide Notice of Redemption        
Debt Instrument [Line Items]        
Threshold trading days | day 2