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Long-term Debt - Convertible Senior Notes Carrying Value (Details) - Senior Notes - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Aug. 31, 2020
Oct. 31, 2018
Oct. 24, 2018
Oct. 22, 2018
Dec. 31, 2016
2024 Notes              
Debt Instrument [Line Items]              
Carrying value $ 81,462,000 $ 0          
Unamortized debt discount and issuance costs 35,589,000 0          
Principal amount $ 117,051,000 0 $ 117,100,000        
Remaining amortization period (years) 3 years 10 months 24 days            
2024 Notes | Level 2              
Debt Instrument [Line Items]              
Fair value $ 153,220,000 0          
2025 Notes              
Debt Instrument [Line Items]              
Carrying value 116,349,000 107,169,000          
Unamortized debt discount and issuance costs 56,151,000 65,331,000          
Principal amount $ 172,500,000 $ 172,500,000   $ 172,500,000 $ 22,500,000 $ 150,000,000.0  
Remaining amortization period (years) 4 years 9 months 18 days 5 years 9 months 18 days          
2025 Notes | Level 2              
Debt Instrument [Line Items]              
Fair value $ 147,488,000 $ 122,048,000          
2021 Notes              
Debt Instrument [Line Items]              
Carrying value 26,557,000 123,237,000          
Unamortized debt discount and issuance costs 180,000 1,763,000          
Principal amount $ 26,737,000 $ 125,000,000         $ 125,000,000.0
Remaining amortization period (years) 10 months 24 days 1 year 10 months 24 days          
2021 Notes | Level 2              
Debt Instrument [Line Items]              
Fair value $ 26,470,000 $ 111,250,000