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Debt - Convertible Senior Notes - Liability and Equity Components (Details) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Liability component    
Outstanding principal balance $ 447,234 $ 447,234
Debt discount and issuance costs, net (58,590) (64,379)
Convertible senior notes | 2025 Notes    
Liability component    
Outstanding principal balance 192,500 192,500
Debt discount and issuance costs, net (56,448) (61,766)
Net carrying amount 136,052 130,734
Equity component, net $ 65,361 $ 65,361