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Note 10 - Financial Instruments - Gain or Loss on Derivatives Not Designated as Hedging Instruments (Details) - USD ($)
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Gain (loss) on derivatives $ 5,154 $ (29,053)
Not Designated as Hedging Instrument [Member]    
Gain (loss) on derivatives 5,154 (29,053)
Not Designated as Hedging Instrument [Member] | Interest Rate Swap Contracts, Fair Value [Member]    
Gain (loss) on derivatives 142,216 (31,351)
Not Designated as Hedging Instrument [Member] | Interest Rate Contracts, Realized (Loss) / Gain [Member]    
Gain (loss) on derivatives $ (137,062) $ 2,298