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Fair Value Measurements - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
Aug. 31, 2021
May 31, 2021
Sep. 30, 2021
Sep. 30, 2021
Dec. 31, 2020
Sep. 30, 2020
1.50% Convertible Senior Notes            
Debt Instrument [Line Items]            
Convertible notes exchanged $ 169,100,000 $ 250,000,000 $ 169,000,000 $ 419,000,000    
Convertible Senior Notes            
Debt Instrument [Line Items]            
Fair value     150,200,000 150,200,000 $ 828,200,000 $ 624,800,000
Senior Notes            
Debt Instrument [Line Items]            
Fair value     $ 622,500,000 $ 622,500,000 $ 602,600,000 $ 566,600,000