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Convertible Senior Notes (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 08, 2018
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Convertible Senior Notes        
Net carrying amount   $ 65,025 $ 63,247  
Convertible Senior Notes        
Convertible Senior Notes        
Principal amount $ 100,000 100,000   $ 100,000
Unamortized debt discount   (33,049)    
Unamortized debt issuance costs   (1,926)    
Net carrying amount   65,025    
Carrying amount of the equity component   37,702    
Other issuance costs $ 894 1,700    
Income tax benefit on equity component   $ 9,200