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Note 10 - Loss / (Gain) Per Common Share - Antidilutive Securities Excluded from the Diluted per Share Calculation (Details) - shares
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Potentially dilutive securities (in shares) 11,982,979 1,291,855
Warrant [Member] | Class B Warrants [Member]    
Potentially dilutive securities (in shares) 0 480,000
Series E Convertible Preferred Stock [Member]    
Potentially dilutive securities (in shares) 11,982,979 811,855