Quarterly report pursuant to Section 13 or 15(d)

Convertible Senior Notes - Narrative (Details)

v3.10.0.1
Convertible Senior Notes - Narrative (Details)
1 Months Ended 2 Months Ended 3 Months Ended 9 Months Ended
Jun. 30, 2018
USD ($)
May 22, 2018
USD ($)
$ / shares
shares
Jun. 19, 2018
USD ($)
$ / shares
May 31, 2018
USD ($)
Aug. 31, 2014
USD ($)
d
$ / shares
shares
Apr. 30, 2018
USD ($)
Sep. 30, 2018
USD ($)
$ / shares
Sep. 30, 2018
USD ($)
$ / shares
Dec. 31, 2017
USD ($)
May 22, 2015
USD ($)
Debt Instrument [Line Items]                    
Carrying value of equity component of convertible notes             $ 0 $ 0 $ 18,859,000  
Derivative asset             509,257,000 509,257,000 0  
Convertible Notes | 2019 Convertible Senior Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount outstanding         $ 245,000,000.0   223,215,000 223,215,000 245,000,000  
Initial conversion rate (shares per $1,000)         0.0133251          
Initial conversion price (USD per share) | $ / shares         $ 75.05          
Interest rate (as a percent)         0.75%          
If-converted value in excess of principal $ 563,200,000 $ 341,600,000                
Increase (decrease) in if-converted value in excess of principal             161,900,000 $ 221,600,000    
Notices for conversion           $ 21,800,000 $ 195,900,000      
Conversion value over the principal amount           31,600,000        
Gain (loss) on extinguishment of debt           $ (600,000)        
Warrants issued in public offering (shares) | shares         3,264,643          
Exercise price of convertible bond hedge (USD per share) | $ / shares   $ 75.05     $ 75.05   $ 75.05 $ 75.05    
Payments for convertible bond hedges         $ 48,100,000          
Bond hedge settlement proceeds             $ 52,100,000      
Derivative asset   $ 340,000,000.0         561,400,000 $ 561,400,000    
Warrant exercise price (USD per share) | $ / shares         $ 125.08          
Value of warrants issued         $ 11,600,000          
Convertible Notes | 2019 Convertible Senior Notes | Debt Instrument, Redemption, Period One                    
Debt Instrument [Line Items]                    
Threshold trading days | d         20          
Consecutive trading days | d         30          
Stock price trigger to classify convertible debt as current (as a percent)         130.00%     130.00%    
Convertible Notes | 2019 Convertible Senior Notes | Debt Instrument, Redemption, Period Two                    
Debt Instrument [Line Items]                    
Threshold trading days | d         5          
Consecutive trading days | d         10          
Maximum threshold of debt trading price trigger (as a percent)         98.00%          
Convertible Notes | 2023 Convertible Senior Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount outstanding   $ 750,000,000         750,000,000 $ 750,000,000 0  
Initial conversion rate (shares per $1,000)       0.0040244            
Initial conversion price (USD per share) | $ / shares   $ 248.48                
Interest rate (as a percent)   0.75%                
Proceeds from debt, net of issuance costs   $ 733,100,000                
Carrying value of equity component of convertible notes             143,986,000 143,986,000 $ 0  
Warrants issued in public offering (shares) | shares   3,018,327                
Exercise price of convertible bond hedge (USD per share) | $ / shares   $ 248.48 $ 248.48              
Payments for convertible bond hedges       $ 140,300,000            
Warrant exercise price (USD per share) | $ / shares   $ 315.38                
Value of warrants issued       $ 90,000,000.0            
Fair value of of the conversion option derivative liability                   $ 144,000,000.0
Interest expense resulting from change in fair value     $ 13,500,000       19,200,000 7,500,000    
Debt issuance costs   $ 16,900,000                
Debt issuance costs related to the equity component of convertible debt   3,200,000                
Debt issuance costs related to the liability component of convertible debt   $ 13,700,000                
Convertible Notes | 2023 Convertible Senior Notes | Debt Instrument, Redemption, Period One                    
Debt Instrument [Line Items]                    
Threshold trading days | d         20          
Consecutive trading days | d         30          
Stock price trigger to classify convertible debt as current (as a percent)         130.00%          
Convertible Notes | 2023 Convertible Senior Notes | Debt Instrument, Redemption, Period Two                    
Debt Instrument [Line Items]                    
Threshold trading days | d         5          
Consecutive trading days | d         10          
Maximum threshold of debt trading price trigger (as a percent)         98.00%          
Measurement Input, Discount Rate | Convertible Notes | 2019 Convertible Senior Notes                    
Debt Instrument [Line Items]                    
Discount rate (as a percent)         0.0583          
Other Expense, Net | Convertible Notes | 2019 Convertible Senior Notes                    
Debt Instrument [Line Items]                    
Net change in fair value of derivatives             $ 162,000,000.0 $ 221,400,000