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Convertible Senior Notes - Narrative (Details)
1 Months Ended 3 Months Ended
May 24, 2018
USD ($)
day
$ / shares
Jun. 30, 2020
USD ($)
May 31, 2018
USD ($)
Jun. 30, 2015
USD ($)
day
$ / shares
Mar. 31, 2021
USD ($)
$ / shares
Dec. 31, 2020
USD ($)
Jun. 05, 2018
USD ($)
Debt Instrument [Line Items]              
Purchase of capped calls $ 65,200,000            
Convertible Senior Notes              
Debt Instrument [Line Items]              
Debt instrument, convertible, conversion ratio       0.0164572      
Conversion price (usd per share) | $ / shares       $ 60.76      
Threshold note trading days | day       5      
Threshold percentage of note price trigger       98.00%      
Purchase price trigger percentage       100.00%      
Redemption price triggered by fundamental change, percentage 100.00%            
Redemption price, percentage 100.00%     100.00%      
Remaining discount and issuance cost, weighted average amortization period         1 year 2 months 12 days    
Convertible Senior Notes | Subsequent to September 30, 2015              
Debt Instrument [Line Items]              
Threshold trading days | day 20     20      
Threshold consecutive trading days | day 30     30      
Threshold percentage of stock price trigger 130.00%     130.00%      
Convertible Senior Notes | On or After June 1, 2020 Until June 1, 2022              
Debt Instrument [Line Items]              
Threshold consecutive trading days | day       30      
Common Stock              
Debt Instrument [Line Items]              
Closing share price (usd per share) | $ / shares         $ 19.57    
Convertible Senior Notes Due 2024 | Convertible Senior Notes              
Debt Instrument [Line Items]              
Principal amount $ 525,000,000.0           $ 75,000,000.0
Interest rate 0.875%            
Initial purchaser's discount $ 15,000,000.0            
Debt issuance costs 600,000            
Proceeds from issuance of convertible senior notes, net of issuance costs 584,400,000            
Repurchase of convertible senior notes 330,400,000            
Purchase of capped calls $ 65,200,000            
Debt instrument, convertible, conversion ratio 0.0431167            
Conversion price (usd per share) | $ / shares $ 23.17            
Threshold note trading days | day 5            
Threshold consecutive note trading days 5 days            
Threshold percentage of note price trigger 98.00%            
Equity component of debt $ 141,700,000            
Remaining discount amortization period         3 years 2 months 12 days    
Cap price (usd per share) | $ / shares $ 34.32            
Debt amount outstanding         $ 600,000,000 $ 600,000,000  
Convertible Senior Notes Due 2024 | Convertible Senior Notes | On or After June 1, 2020 Until June 1, 2022              
Debt Instrument [Line Items]              
Threshold trading days | day 20            
Threshold percentage of stock price trigger 130.00%            
Convertible Senior Notes Due 2024 | Measurement Input, Discount Rate | Convertible Senior Notes              
Debt Instrument [Line Items]              
Measurement input 0.055            
Series A Notes | Convertible Senior Notes              
Debt Instrument [Line Items]              
Principal amount       $ 460,000,000.0      
Interest rate       1.00%      
Repurchase of convertible senior notes     $ 330,400,000        
Repurchased principal amount of debt $ 340,200,000 $ 96,400,000 340,200,000        
Equity component of debt, subsequent adjustments     $ 13,000,000.0        
Remaining expected life     2 years        
Gain (loss) on repurchase of convertible senior notes   0 $ (10,800,000)        
Extinguishment of debt, amount   $ 96,400,000          
Debt amount outstanding         23,436,000 23,436,000  
Series A Notes | Measurement Input, Discount Rate | Convertible Senior Notes              
Debt Instrument [Line Items]              
Measurement input     0.045        
Series A Notes | Convertible senior notes | Convertible Senior Notes              
Debt Instrument [Line Items]              
Repurchase of convertible senior notes     $ 317,400,000        
Series B Notes | Convertible Senior Notes              
Debt Instrument [Line Items]              
Principal amount       $ 460,000,000.0      
Interest rate       1.625%      
Initial purchaser's discount       $ 23,000,000.0      
Debt issuance costs       500,000      
Proceeds from issuance of convertible senior notes, net of issuance costs       $ 896,500,000      
Threshold consecutive note trading days       5 days      
Debt amount outstanding         $ 460,000,000 $ 460,000,000  
Series B Notes | Convertible Senior Notes | On or After June 1, 2020 Until June 1, 2022              
Debt Instrument [Line Items]              
Threshold trading days | day       20      
Threshold percentage of stock price trigger       130.00%      
Required trading days since notice of redemption, not more than       3 days      
Debt, Liability Component | Convertible Senior Notes              
Debt Instrument [Line Items]              
Initial purchaser's discount 11,500,000     $ 17,600,000      
Debt issuance costs 500,000     400,000      
Carrying amount of convertible debt 458,300,000            
Debt, Equity Component | Convertible Senior Notes              
Debt Instrument [Line Items]              
Initial purchaser's discount 3,500,000     5,400,000      
Debt issuance costs $ 100,000     $ 100,000