Quarterly report pursuant to Section 13 or 15(d)

Note 6 - Stockholder's Equity (Details Textual)

v3.21.2
Note 6 - Stockholder's Equity (Details Textual) - USD ($)
 1 Months Ended 9 Months Ended
Sep. 03, 2021
Mar. 31, 2021
Feb. 28, 2021
Jan. 31, 2021
Sep. 30, 2020
Aug. 31, 2020
May 31, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Proceeds From Issuance of Common Stock, Net of Issuance Costs               $ 33,390,000 $ 14,356,000  
Common Stock, Par or Stated Value Per Share (in dollars per share)               $ 0.001   $ 0.001
January 2021 Offering [Member]                    
Stock Issued During Period, Shares, New Issues (in shares)       3,076,924            
Shares Issued, Price Per Share (in dollars per share)       $ 2.60            
Proceeds From Issuance of Common Stock, Net of Issuance Costs       $ 8,000,000.0            
Payments of Stock Issuance Costs       $ 73,000            
February 2021 Offering [Member]                    
Stock Issued During Period, Shares, New Issues (in shares)     2,926,830              
Shares Issued, Price Per Share (in dollars per share)     $ 4.10              
Proceeds From Issuance of Common Stock, Net of Issuance Costs     $ 12,000,000.0              
Payments of Stock Issuance Costs     $ 70,000              
March 2021 Offering [Member]                    
Stock Issued During Period, Shares, New Issues (in shares)   1,512,499                
Shares Issued, Price Per Share (in dollars per share)   $ 9.00                
Proceeds From Issuance of Common Stock, Net of Issuance Costs   $ 13,600,000                
Payments of Stock Issuance Costs   $ 72,000                
Sales Agreement [Member]                    
Stock Issuance Program, Authorized Amount $ 75,000,000                  
Common Stock, Par or Stated Value Per Share (in dollars per share) $ 0.001                  
Stock Issuance Program, Commission Percent 3.00%                  
May 2020 Offering [Member]                    
Stock Issued During Period, Shares, New Issues (in shares)             1,825,000      
Shares Issued, Price Per Share (in dollars per share)             $ 3.50      
Proceeds From Issuance of Common Stock, Net of Issuance Costs             $ 6,000,000.0      
May 2020 Offering [Member] | Differentiate From $319,000 [Member]                    
Payments of Stock Issuance Costs             319,000      
Payments of Other Offering Expenses             $ 116,000      
August 2020 Offering [Member]                    
Stock Issued During Period, Shares, New Issues (in shares)           4,540,541        
Shares Issued, Price Per Share (in dollars per share)           $ 1.85        
Proceeds From Issuance of Common Stock, Net of Issuance Costs           $ 7,600,000        
Payments of Stock Issuance Costs           588,000        
Payments of Other Offering Expenses           $ 180,000        
Over-Allotment Option [Member]                    
Stock Issued During Period, Shares, New Issues (in shares)         448,440          
Proceeds From Issuance of Common Stock, Net of Issuance Costs         $ 771,000          
Payments of Stock Issuance Costs         $ 58,000          
Stock Issuance Program, Authorized Shares (in shares)           681,081