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Convertible Senior Notes - Net Carrying Amount (Details) - Senior Notes - USD ($)
Sep. 30, 2021
Dec. 31, 2020
Aug. 31, 2020
Apr. 30, 2019
Mar. 31, 2019
Apr. 30, 2018
Carrying Amount | Fair Value, Measurements, Nonrecurring            
Debt Instrument [Line Items]            
Net carrying amount $ 1,676,749,000 $ 1,506,922,000        
2026 Notes            
Debt Instrument [Line Items]            
Principal 1,000,000,000 1,000,000,000 $ 1,000,000,000      
Unamortized debt discount 0 (226,732,000)        
Unamortized issuance costs (12,973,000) (11,338,000)        
2026 Notes | Carrying Amount | Fair Value, Measurements, Nonrecurring            
Debt Instrument [Line Items]            
Net carrying amount 987,027,000 761,930,000        
2025 Notes            
Debt Instrument [Line Items]            
Principal 699,989,000 800,000,000   $ 100,000,000 $ 700,000,000  
Unamortized debt discount 0 (149,138,000)        
Unamortized issuance costs (10,267,000) (10,248,000)        
2025 Notes | Carrying Amount | Fair Value, Measurements, Nonrecurring            
Debt Instrument [Line Items]            
Net carrying amount 689,722,000 640,614,000        
2023 Notes            
Debt Instrument [Line Items]            
Principal   115,576,000       $ 345,000,000
Unamortized debt discount   (9,953,000)        
Unamortized issuance costs   (1,245,000)        
2023 Notes | Carrying Amount | Fair Value, Measurements, Nonrecurring            
Debt Instrument [Line Items]            
Net carrying amount $ 0 $ 104,378,000