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Fair Value of Financial Instruments - Additional Information (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2020
Mar. 31, 2020
Dec. 31, 2019
Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Long-term investments in convertible and redeemable preferred stock $ 173,641,000 $ 173,641,000   $ 132,188,000  
Unrealized gain 23,300,000 38,600,000      
Level 2          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Long-term investments in convertible and redeemable preferred stock 0 0   $ 0  
Convertible senior notes due 2026 | Convertible Debt          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Principal $ 650,000,000 $ 650,000,000      
Debt instrument, interest rate (percentage) 0.00% 0.00%      
Convertible senior notes due 2026 | Level 2          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Debt instrument, interest rate (percentage) 0.00% 0.00%      
Fair value of convertible senior notes $ 644,600,000 $ 644,600,000      
Convertible senior notes due 2025 | Convertible Debt          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Principal $ 1,000,000,000 $ 1,000,000,000 $ 1,000,000,000.0    
Debt instrument, interest rate (percentage)     0.00%    
Convertible senior notes due 2025 | Level 2          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Debt instrument, interest rate (percentage) 0.00% 0.00%      
Fair value of convertible senior notes $ 1,100,000,000 $ 1,100,000,000      
Convertible senior notes due 2023          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Principal $ 101,787,000 $ 101,787,000      
Debt instrument, interest rate (percentage)         0.00%
Convertible senior notes due 2023 | Level 2          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Debt instrument, interest rate (percentage) 0.00% 0.00%      
Fair value of convertible senior notes $ 341,900,000 $ 341,900,000