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Convertible Senior Notes - Equity and Liability Components of Financing Arrangements (Details) - Convertible Notes - USD ($)
Dec. 31, 2019
Dec. 31, 2018
May 22, 2018
Aug. 31, 2014
Notes Payable, Current and Noncurrent        
Total current portion of notes payable   $ 26,433,000    
Total long-term portion of notes payable $ 638,959,000 609,864,000    
Fair value of convertible senior notes outstanding (Level 2) 647,280,000 713,533,000    
2019 Convertible Senior Notes        
Notes Payable, Current and Noncurrent        
Principal amount outstanding 0 27,326,000   $ 245,000,000.0
Unamortized discount 0 (893,000)    
2023 Convertible Senior Notes        
Notes Payable, Current and Noncurrent        
Principal amount outstanding 750,000,000 750,000,000 $ 750,000,000  
Unamortized discount (111,041,000) (140,136,000)    
Carrying value of equity component of 2023 Notes $ 101,422,000 $ 127,997,000