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Convertible Senior Notes - Narrative - Convertible Senior Notes (Details)
1 Months Ended 3 Months Ended 12 Months Ended
May 24, 2018
USD ($)
$ / shares
May 24, 2018
USD ($)
day
$ / shares
May 24, 2018
USD ($)
$ / shares
May 24, 2018
USD ($)
$ / shares
May 24, 2018
USD ($)
days
$ / shares
May 31, 2018
USD ($)
Jun. 30, 2015
USD ($)
Jun. 30, 2015
USD ($)
day
Jun. 30, 2015
USD ($)
Jun. 30, 2015
USD ($)
Jun. 30, 2015
USD ($)
days
Mar. 31, 2020
USD ($)
$ / shares
Dec. 31, 2018
USD ($)
Dec. 31, 2019
USD ($)
Jun. 05, 2018
USD ($)
Dec. 31, 2015
USD ($)
$ / shares
Debt Instrument [Line Items]                                
Purchase of capped calls                         $ 65,200,000      
Convertible Senior Notes                                
Debt Instrument [Line Items]                                
Shares of common stock (per $1000 principal amount of notes)                 0.0164572              
Conversion price (usd per share) | $ / shares                               $ 60.76
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                       2 years 1 month 6 days        
Convertible Senior Notes | Subsequent to September 30, 2015                                
Debt Instrument [Line Items]                                
Threshold trading days | day   20           20                
Threshold consecutive trading days   30     30     30     30          
Threshold percentage of stock price trigger     130.00%           130.00%              
Convertible Senior Notes | Convertible Senior Notes due 2024                                
Debt Instrument [Line Items]                                
Principal amount $ 525,000,000.0 $ 525,000,000.0 $ 525,000,000.0 $ 525,000,000.0 $ 525,000,000.0                   $ 75,000,000.0  
Initial purchaser's discount 15,000,000.0 15,000,000.0 15,000,000.0 15,000,000.0 15,000,000.0                      
Debt issuance costs $ 600,000 $ 600,000 $ 600,000 600,000 $ 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                        
Interest rate 0.875% 0.875% 0.875% 0.875% 0.875%                      
Shares of common stock (per $1000 principal amount of notes)                       0.0431167        
Conversion price (usd per share) | $ / shares $ 23.17 $ 23.17 $ 23.17 $ 23.17 $ 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                       4 years 2 months 12 days        
Cap price (usd per share) | $ / shares $ 34.32 $ 34.32 $ 34.32 $ 34.32 $ 34.32                      
Debt amount outstanding                       $ 600,000,000   $ 600,000,000    
Convertible Senior Notes | Convertible Senior Notes due 2024 | 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 | Series A Notes                                
Debt Instrument [Line Items]                                
Principal amount             $ 460,000,000.0 $ 460,000,000.0 $ 460,000,000.0 $ 460,000,000.0 $ 460,000,000.0          
Repurchase of convertible senior notes           $ 330,400,000                    
Repurchased principal amount of debt $ 340,200,000 $ 340,200,000 $ 340,200,000 $ 340,200,000 $ 340,200,000 340,200,000                    
Interest rate             1.00% 1.00% 1.00% 1.00% 1.00%          
Threshold note trading days | day               5                
Threshold consecutive note trading days             5 days                  
Equity component of debt, subsequent adjustments           $ 13,000,000.0                    
Remaining expected life           2 years                    
Loss on repurchase of convertible senior notes           $ 10,800,000                    
Debt amount outstanding                       119,828,000   119,828,000    
Convertible Senior Notes | Series B Notes                                
Debt Instrument [Line Items]                                
Principal amount             $ 460,000,000.0 $ 460,000,000.0 $ 460,000,000.0 $ 460,000,000.0 $ 460,000,000.0          
Initial purchaser's discount             23,000,000.0 23,000,000.0 23,000,000.0 23,000,000.0 23,000,000.0          
Debt issuance costs             $ 500,000 $ 500,000 $ 500,000 500,000 $ 500,000          
Proceeds from issuance of convertible senior notes, net of issuance costs                   $ 896,500,000            
Interest rate             1.625% 1.625% 1.625% 1.625% 1.625%          
Debt amount outstanding                       $ 460,000,000   $ 460,000,000    
Convertible Senior Notes | Series B 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                  
Convertible Senior Notes | Debt, Liability Component                                
Debt Instrument [Line Items]                                
Initial purchaser's discount 11,500,000 11,500,000 11,500,000 11,500,000 11,500,000                     $ 17,600,000
Debt issuance costs 500,000 500,000 500,000 500,000 500,000                     400,000
Carrying amount of convertible debt 458,300,000 458,300,000 458,300,000 458,300,000 458,300,000                      
Convertible Senior Notes | Debt, Equity Component                                
Debt Instrument [Line Items]                                
Initial purchaser's discount 3,500,000 3,500,000 3,500,000 3,500,000 3,500,000                     5,400,000
Debt issuance costs $ 100,000 $ 100,000 $ 100,000 $ 100,000 $ 100,000                     $ 100,000
Measurement Input, Discount Rate | Convertible Senior Notes | Convertible Senior Notes due 2024                                
Debt Instrument [Line Items]                                
Discount rate 0.055 0.055 0.055 0.055 0.055                      
Measurement Input, Discount Rate | Convertible Senior Notes | Series A Notes                                
Debt Instrument [Line Items]                                
Discount rate           0.045                    
Common Stock                                
Debt Instrument [Line Items]                                
Closing share price (usd per share) | $ / shares                       $ 10.58        
Convertible senior notes | Convertible Senior Notes | Series A Notes                                
Debt Instrument [Line Items]                                
Repurchase of convertible senior notes           $ 317,400,000