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Convertible Notes Convertible Notes (Summary of December 2021 Notes) (Details) - USD ($)
$ in Thousands
Mar. 31, 2020
Dec. 31, 2019
Nov. 22, 2016
Nov. 20, 2015
Debt Instrument [Line Items]        
Debt Instrument, Face Amount $ 14,805      
December 2021 Notes [Member]        
Debt Instrument [Line Items]        
Debt Instrument, Face Amount 13,805 $ 19,170    
Debt Instrument, Unamortized Discount (1,403) (2,220) $ (4,300)  
Convertible notes $ 12,402 $ 16,950 $ 150,000 $ 150,000