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Debt - Convertible Senior Notes, Notes Hedges, Warrants Narrative (Details)
3 Months Ended 6 Months Ended
Jul. 31, 2021
USD ($)
$ / shares
shares
Apr. 30, 2021
shares
Jul. 31, 2020
USD ($)
Jul. 31, 2021
USD ($)
trading_day
$ / shares
shares
Jan. 31, 2021
shares
Jul. 31, 2020
USD ($)
Feb. 01, 2021
Sep. 30, 2017
USD ($)
Jun. 30, 2013
USD ($)
Debt Instrument [Line Items]                  
Payments on convertible senior notes | $ $ 20,000   $ 249,945,000 $ 71,000   $ 249,946,000      
Number of trading days related to warrants (in days) | trading_day       60          
2020 Notes                  
Debt Instrument [Line Items]                  
Convertible senior notes, principal amount | $                 $ 250,000,000
Class A | 2020 Notes                  
Debt Instrument [Line Items]                  
Warrants settled (shares)         1,600,000        
Class of warrant outstanding (in shares) 0     0          
Class A | 2022 Notes                  
Debt Instrument [Line Items]                  
Convertible senior notes, principal amount | $ $ 1,000     $ 1,000          
Debt instrument, convertible, number of shares       6.7982          
Warrants expires in 2020                  
Debt Instrument [Line Items]                  
Shares covered by each purchased options or warrants (in shares) 3,100,000     3,100,000          
Number of trading days related to warrants (in days) | trading_day       60          
Exercise price of warrants (in dollars per share) | $ / shares $ 107.96     $ 107.96          
Warrants expires In 2023                  
Debt Instrument [Line Items]                  
Shares covered by each purchased options or warrants (in shares) 7,800,000     7,800,000          
Number of trading days related to warrants (in days) | trading_day       60          
Exercise price of warrants (in dollars per share) | $ / shares $ 213.96     $ 213.96          
Convertible Debt | 2020 Notes                  
Debt Instrument [Line Items]                  
Contractual interest rate                 1.50%
Payments on convertible senior notes | $ $ 250,000,000                
Convertible Debt | 2022 Notes                  
Debt Instrument [Line Items]                  
Contractual interest rate             0.25% 0.25%  
Convertible senior notes, principal amount | $               $ 1,150,000,000  
Repurchase of notes percentage       100.00%          
Carrying amount of the equity component | $               $ 223,000,000  
Effective interest rate of liability component 0.55%     0.55%       4.60%  
Liability issuance costs | $               $ 14,000,000  
Equity issuance costs | $               $ 4,000,000  
Convertible Debt | Class A | 2020 Notes                  
Debt Instrument [Line Items]                  
Debt conversion, converted instrument, shares issued   1,700,000              
Initial conversion price (in dollars per share) | $ / shares $ 81.74     $ 81.74          
Indexed shares (in shares) 3,100,000     3,100,000          
Purchase of treasury stock from the exercise of convertible senior notes hedges (in shares)       1,700,000          
Convertible Debt | Class A | 2022 Notes                  
Debt Instrument [Line Items]                  
Initial conversion price (in dollars per share) | $ / shares $ 147.10     $ 147.10          
Indexed shares (in shares) 7,800,000     7,800,000          
Convertible Debt | Debt Conversion, Option One | Convertible Senior Notes                  
Debt Instrument [Line Items]                  
Threshold trading days (in trading days) | trading_day       20          
Threshold consecutive trading days | trading_day       30          
Threshold percentage of conversion price       130.00%          
Convertible Debt | Debt Conversion, Option Two | Convertible Senior Notes                  
Debt Instrument [Line Items]                  
Threshold trading days (in trading days) | trading_day       5          
Threshold consecutive trading days | trading_day       5          
Convertible Debt | Debt Conversion, Option Two | Convertible Senior Notes | Maximum                  
Debt Instrument [Line Items]                  
Threshold percentage of stock trading price       98.00%