Quarterly report pursuant to Section 13 or 15(d)

Note 9 - Shareholders' Equity (Details Textual)

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Note 9 - Shareholders' Equity (Details Textual) - USD ($)
 3 Months Ended 9 Months Ended
Sep. 26, 2021
Apr. 10, 2020
Feb. 13, 2020
Mar. 31, 2021
Mar. 31, 2020
Sep. 30, 2021
Sep. 30, 2020
Sep. 11, 2020
Stock Issued During Period, Shares, New Issues (in shares) 7,653,060 4,600,000 2,125,000          
Shares Issued, Price Per Share (in dollars per share) $ 3.92 $ 5.00 $ 4.00          
Proceeds from Issuance of Common Stock $ 30,000,000.0 $ 23,000,000.0 $ 8,500,000     $ 29,867,000 $ 28,872,000  
Proceeds from Issuance of Common Stock, Net $ 29,900,000 $ 21,200,000 $ 7,700,000          
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)           40,000 7,200  
Stock Issued During Period, Value, Stock Options Exercised       $ 244,000 $ 16,000 $ 244,000 $ 16,000  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value           $ 132,000 $ 22,000  
Stock Issued During Period, Shares, Exercise of Common Stock Warrants (in shares)           0    
Warrant Issued for Strategic Advisory Services [Member] | Craig-Hallum Capital Group LLC [Member]                
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)               10,000
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)               $ 4.00
Warrants Issued in Private Placement [Member]                
Stock Issued During Period, Shares, Exercise of Common Stock Warrants (in shares)             0