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Organization and Operations (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Jan. 30, 2020
Feb. 06, 2019
Dec. 31, 2020
Dec. 31, 2019
Common Stock        
Gross proceeds from public offering     $ 16,270 $ 6,996
Accumulated deficit     (260,897) $ (223,597)
Cash, cash equivalents and short-term investments     44,900  
Revenue     0  
Net proceeds     $ 104,000  
Series X Preferred Stock        
Common Stock        
Number of shares issued     86,077  
Shares issued     86,077  
Series X Common shares, As converted        
Common Stock        
Shares agreed to issue upon shareholders approval     86,077,000  
Private Placement        
Common Stock        
Gross proceeds     $ 110,000  
Common Stock        
Common Stock        
Number of shares issued     2,353,737 1,282,904
Gross proceeds from public offering     $ 3 $ 1
Shares issued     2,353,737 1,282,904
Common Stock | ATM        
Common Stock        
Number of shares issued     2,353,737  
Share price (in dollars per share)     $ 7.13  
Gross proceeds from public offering     $ 16,800  
Proceeds from public offering, net of issuance costs     $ 16,300  
Shares issued     2,353,737  
Common Stock | Cowen        
Common Stock        
Percentage of commission paid to underwriter based on proceeds from common stock     3.00%  
Remaining available under sales agreement     $ 27,900  
Common Stock | Oppenheimer & Co. Inc | February 2019 Financing        
Common Stock        
Number of shares issued   4,000,000    
Number of warrants issued   2,000,000    
Warrants price (in dollars per unit)   $ 5.00    
Proceeds from public offering, net of issuance costs   $ 18,500    
Shares issued   4,000,000    
Common Stock | Oppenheimer & Co. Inc | Over-Allotment option        
Common Stock        
Number of shares issued 20.0      
Shares issued 20.0      
Common Stock | Oppenheimer & Co. Inc | January 2020 Financing        
Common Stock        
Number of shares issued 5,290,000      
Share price (in dollars per share) $ 5.00      
Gross proceeds from public offering $ 26,500      
Proceeds from public offering, net of issuance costs $ 24,600      
Shares issued 5,290,000