Quarterly report pursuant to Section 13 or 15(d)

Capitalization and Equity Structure - Additional Information (Details)

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Capitalization and Equity Structure - Additional Information (Details) - USD ($)
 1 Months Ended 2 Months Ended 3 Months Ended 6 Months Ended
Oct. 29, 2020
Jun. 30, 2020
Dec. 31, 2019
May 30, 2019
Feb. 28, 2021
Jun. 30, 2021
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
May 31, 2019
Class of Stock [Line Items]                    
Common stock, shares authorized (in shares)           141,429,000 141,429,000   141,429,000  
Preferred Stock, shares authorized (in shares)           10,000,000 10,000,000   10,000,000  
Common stock, shares issued (in shares)           12,655,000 12,655,000   8,349,000  
Common stock, shares outstanding (in shares)           12,655,000 12,655,000   8,349,000  
Preferred stock, shares issued (in shares)           0 0   0  
Preferred stock, shares outstanding (in shares)           0 0   0  
Proceeds from direct offering             $ 37,295,000 $ 7,082,000    
Warrants issued (in shares)             273,000      
Value of shares sold             $ 1,417,000 $ 785,000    
Warrants exercised (in shares)             (358,000) 223,000    
Number warrants called (in shares)           1,240,000 1,240,000   1,325,000  
February 2021 Offering                    
Class of Stock [Line Items]                    
Percentage of warrants issued to purchase shares of common stock         7.00%          
Exercise price (in dollars per share)         $ 12.81          
2021 Warrants                    
Class of Stock [Line Items]                    
Warrants issued (in shares)         273,000   273,000      
Exercise price (in dollars per share)         $ 12.81 $ 12.81 $ 12.81      
Warrants exercised (in shares)             0      
Duration of put option         30 days          
Put option pay period         5 days          
Number warrants called (in shares)           273,000 273,000   0  
Class of warrant or right expiration period         5 years   5 years      
June 2020 Investor Warrants                    
Class of Stock [Line Items]                    
Warrants issued (in shares)             0      
Exercise price (in dollars per share)   $ 5.18       $ 5.18 $ 5.18 $ 5.18    
Warrants exercised (in shares)             (270,000) 0    
Duration of put option   30 days                
Number warrants called (in shares)   874,000       127,000 127,000 874,000 397,000  
Class of warrant or right expiration period             5 years 6 months      
June 2020 Placement Agent Warrants                    
Class of Stock [Line Items]                    
Warrants issued (in shares)   122,000         0      
Exercise price (in dollars per share)           $ 5.64 $ 5.64      
Warrants exercised (in shares)             (83,000) 0    
Number warrants called (in shares)           39,000 39,000   122,000  
Class of warrant or right expiration period             5 years      
December 2019 Warrants                    
Class of Stock [Line Items]                    
Warrants issued (in shares)             0      
Exercise price (in dollars per share)     $ 8.10     $ 8.10 $ 8.10      
Warrants exercised (in shares)             0      
Duration of put option     30 days              
Put option pay period     5 days              
Number warrants called (in shares)     556,000     556,000 556,000   556,000  
Class of warrant or right expiration period     5 years       5 years      
December 2019 Placement Agent Warrants                    
Class of Stock [Line Items]                    
Warrants issued (in shares)             0      
Exercise price (in dollars per share)     $ 8.44     $ 8.44 $ 8.44      
Warrants exercised (in shares)             0      
Number warrants called (in shares)     52,000     52,000 52,000   52,000  
Class of warrant or right expiration period             5 years      
May 2019 Warrants                    
Class of Stock [Line Items]                    
Warrants issued (in shares)             0      
Exercise price (in dollars per share)   $ 3.52       $ 3.52 $ 3.52 $ 3.52   $ 3.52
Warrants exercised (in shares)             (5,000) 0    
Duration of put option       90 days            
Number warrants called (in shares)           193,000 193,000   198,000 444,000
Class of warrant or right expiration period             5 years      
June 2020 Warrants                    
Class of Stock [Line Items]                    
Exercise price (in dollars per share)   5.18           $ 5.18    
Class of warrant or right expiration period             5 years 6 months      
Underwriting agreement | February 2021 Offering                    
Class of Stock [Line Items]                    
Number warrants called (in shares)         3,902,000          
Sale of shares (in dollars per share)         $ 10.25          
Value of shares sold         $ 40,000,000          
Proceeds from direct offering         $ 36,504,000          
Expected term         5 years          
At-The-Market Offering                    
Class of Stock [Line Items]                    
Number warrants called (in shares)           0 78,000      
Sale of shares (in dollars per share) $ 6.75         $ 10.72 $ 10.72      
Value of shares sold $ 7,500,000                  
Commission and issuance costs             $ 791,000      
Common Stock | At-The-Market Offering                    
Class of Stock [Line Items]                    
Available for future offerings             $ 6,668,000      
Common Stock | Direct Offering | May 2019 Warrants                    
Class of Stock [Line Items]                    
Sale of shares (in dollars per share)   $ 4.51           $ 4.51