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Convertible Senior Notes, Net - Note Hedges and Warrants (Details)
$ / shares in Units, shares in Thousands
1 Months Ended 3 Months Ended
Sep. 30, 2019
USD ($)
shares
Apr. 30, 2020
USD ($)
day
$ / shares
shares
Apr. 30, 2019
shares
Jan. 31, 2020
USD ($)
Debt Instrument [Line Items]        
Antidilutive securities excluded from computation of earnings per share (in shares) | shares   26,909 36,073  
Convertible Senior Notes Due 2023        
Debt Instrument [Line Items]        
Shares issuable under warrants granted (in shares) | shares 4,600      
Number of warrants issued subject to anti-dilution adjustments (in shares) | shares   2,500    
Value of shares issuable under warrants granted (in dollars per share) | $ / shares   $ 68.06    
Proceeds from issuance of warrants related to 2023 convertible senior notes   $ 52,400,000    
Payments for repurchase of Warrants $ 358,600,000      
Limitation on sale of common stock due to sale price threshold (in days) | day   80    
Convertible Senior Notes Due 2025        
Debt Instrument [Line Items]        
Redemption price percentage   130.00%    
Initial cap price of capped calls (in dollars per share) | $ / shares   $ 255.88    
Purchase of capped call on convertible debt   $ 74,100,000    
Senior Notes | Convertible Senior Notes Due 2023        
Debt Instrument [Line Items]        
Shares issuable under warrants granted (in shares) | shares 4,600 7,100    
Conversion price (in dollars per share) | $ / shares   $ 48.36    
Purchases of hedges related to 2023 convertible senior notes   $ 80,000,000.0    
Proceeds from hedges related to 2023 convertible senior notes $ 405,900,000      
Number of warrants issued subject to anti-dilution adjustments (in shares) | shares   7,100    
Fixed interest rate   0.25%    
Initial conversion rate of common stock   0.0206795    
Limitation on sale of common stock due to sale price threshold (in days) | day   30    
Redemption price percentage   100.00%    
Percentage of closing sale price in excess of convertible notes   98.00%    
Effective interest rate 4.00% 5.68%    
Issuance costs   $ 10,000,000.0   $ 3,800,000
Unamortized debt issuance expense   $ 7,700,000    
Senior Notes | Convertible Senior Notes Due 2025        
Debt Instrument [Line Items]        
Conversion price (in dollars per share) | $ / shares   $ 188.71    
Fixed interest rate   0.125%    
Proceeds from issuance of debt   $ 1,040,700,000    
Initial conversion rate of common stock   0.0052991    
Limitation on sale of common stock due to sale price threshold (in days) | day   30    
Redemption price percentage   100.00%    
Percentage of closing sale price in excess of convertible notes   98.00%    
Sales price of redemption as a percentage of conversion price   130.00%    
Senior notes redeemed   $ 0    
Effective interest rate   4.10%    
Issuance costs   $ 19,300,000    
Unamortized debt issuance expense   15,300,000    
Additional Paid-in Capital | Senior Notes | Convertible Senior Notes Due 2023        
Debt Instrument [Line Items]        
Issuance costs attributable to equity component   811,000    
Additional Paid-in Capital | Senior Notes | Convertible Senior Notes Due 2025        
Debt Instrument [Line Items]        
Issuance costs attributable to equity component   $ 4,040,000    
Shares related to convertible senior notes | Convertible Senior Notes Due 2023        
Debt Instrument [Line Items]        
Antidilutive securities excluded from computation of earnings per share (in shares) | shares   2,494 7,134  
Shares related to convertible senior notes | Convertible Senior Notes Due 2025        
Debt Instrument [Line Items]        
Antidilutive securities excluded from computation of earnings per share (in shares) | shares   5,617 0