Quarterly report pursuant to Section 13 or 15(d)

Note 5 - Equity (Details Textual)

v3.21.1
Note 5 - Equity (Details Textual) - USD ($)
1 Months Ended 3 Months Ended
Feb. 28, 2021
Jan. 31, 2021
Feb. 29, 2020
Mar. 31, 2021
Mar. 31, 2020
Proceeds from Issuance of Common Stock       $ 74,685,000 $ 5,291,000
Stock Issued During Period, Shares, Warrant Exercises (in shares)       10,000  
Proceeds from Warrant Exercises       $ 63,000 $ 0
The 2015 Stock Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)       726,493  
Warrants Issued in Connection with the February 2020 Stock Offering [Member]          
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)     937,501    
February 2021 Stock Offering [Member]          
Stock Issued During Period, Shares, New Issues (in shares) 14,273,684        
Shares Issued, Price Per Share (in dollars per share) $ 4.75        
Proceeds from Issuance of Common Stock $ 78,000,000.0        
Over-Allotment Option [Member]          
Stock Issued During Period, Shares, New Issues (in shares) 2,141,052        
The 2020 ATM Agreement [Member]          
Stock Issued During Period, Shares, New Issues (in shares)   468,684      
Proceeds from Issuance of Common Stock   $ 2,900,000      
February 2020 Stock Offering [Member]          
Stock Issued During Period, Shares, New Issues (in shares)     1,250,000    
Shares and Warrants Issued in Period, Purchase Price Per Share and Related Warrant (in dollars per share)     $ 4.80    
Proceeds from Issuance or Sale of Equity, Total     $ 6,000,000.0