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Convertible Senior Notes (Details)
1 Months Ended 12 Months Ended
Apr. 30, 2018
USD ($)
day
$ / shares
shares
Feb. 02, 2020
USD ($)
$ / shares
Oct. 31, 2019
$ / shares
Apr. 30, 2019
$ / shares
Jan. 31, 2019
USD ($)
Apr. 04, 2018
$ / shares
Debt Instrument [Line Items]            
Debt issuance costs, net of amortization $ 12,900,000          
Capped Call            
Debt Instrument [Line Items]            
Payment to enter into agreement 64,600,000          
Convertible Senior Notes            
Debt Instrument [Line Items]            
Principal amount   $ 575,000,000.0        
Debt issuance costs, net of amortization 9,800,000 6,615,000     $ 8,450,000  
Additional Paid-In Capital            
Debt Instrument [Line Items]            
Debt issuance costs, net of amortization $ 3,100,000 $ 3,068,000        
Common stock            
Debt Instrument [Line Items]            
Closing price of stock (in dollars per share) | $ / shares   $ 17.80 $ 17.80     $ 19.83
Common stock | Capped Call            
Debt Instrument [Line Items]            
Exercise price (in dollars per share) | $ / shares $ 39.66     $ 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          
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%    
Redemption percentage of principal amount of Notes to be redeemed 100.00%          
Convertible debt, fair value based on the closing trading price per $100 of the Notes   $ 582,600,000     $ 558,200,000  
If-converted value   $ 389,500,000        
Remaining term of the notes   38 months        
Convertible Senior Notes | Any Fiscal Quarter Commencing After the Fiscal Quarter Ending on July 31, 2018            
Debt Instrument [Line Items]            
Threshold percentage of stock price trigger 130.00%          
Convertible Senior Notes | Common stock            
Debt Instrument [Line Items]            
Converted Instrument (in shares) | shares 21,884,155          
Conversion ratio (in shares per $1,000 principal amount) 38.0594          
Conversion price (in dollars per share) | $ / shares $ 26.27          
Convertible Senior Notes | Common stock | 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 | Common stock | 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 | Common stock | Immediately Preceding the Date on Which We Provide Notice of Redemption            
Debt Instrument [Line Items]            
Threshold trading days | day 2