Quarterly report pursuant to Section 13 or 15(d)

Capitalization and Equity Structure - Warrants (Details)

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Capitalization and Equity Structure - Warrants (Details) - $ / shares
shares in Thousands
 3 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Class Of Warrant Or Right, Outstanding [Roll Forward]    
Beginning balance (in shares) 1,178  
Expired (in shares) (6)  
Ending balance (in shares) 1,172  
December 2019 Warrants    
Schedule of Capitalization, Equity [Line Items]    
Exercise price (in dollars per share) $ 8.10  
Term (Years) 5 years  
Class Of Warrant Or Right, Outstanding [Roll Forward]    
Beginning balance (in shares) 556  
Expired (in shares) 0  
Ending balance (in shares) 556  
December 2019 Placement Agent Warrants    
Schedule of Capitalization, Equity [Line Items]    
Exercise price (in dollars per share) $ 8.44  
Term (Years) 5 years  
Class Of Warrant Or Right, Outstanding [Roll Forward]    
Beginning balance (in shares) 52  
Expired (in shares) 0  
Ending balance (in shares) 52  
May 2019 Warrants    
Schedule of Capitalization, Equity [Line Items]    
Exercise price (in dollars per share) $ 5.70  
Term (Years) 5 years  
Class Of Warrant Or Right, Outstanding [Roll Forward]    
Beginning balance (in shares) 444  
Expired (in shares) 0  
Ending balance (in shares) 444  
2017 Information Agent Warrants    
Schedule of Capitalization, Equity [Line Items]    
Exercise price (in dollars per share) $ 22.50  
Term (Years) 3 years  
Class Of Warrant Or Right, Outstanding [Roll Forward]    
Beginning balance (in shares) 13  
Expired (in shares) 0  
Ending balance (in shares) 13  
2015 Warrants    
Schedule of Capitalization, Equity [Line Items]    
Exercise price (in dollars per share) $ 41.25 $ 56.10
Term (Years) 5 years  
Class Of Warrant Or Right, Outstanding [Roll Forward]    
Beginning balance (in shares) 107  
Expired (in shares) 0  
Ending balance (in shares) 107  
Pre-2014 warrants    
Schedule of Capitalization, Equity [Line Items]    
Exercise price (in dollars per share) $ 144.90  
Class Of Warrant Or Right, Outstanding [Roll Forward]    
Beginning balance (in shares) 6  
Expired (in shares) (6)  
Ending balance (in shares) 0  
Pre-2014 warrants | Minimum    
Schedule of Capitalization, Equity [Line Items]    
Term (Years) 9 years  
Pre-2014 warrants | Maximum    
Schedule of Capitalization, Equity [Line Items]    
Term (Years) 10 years