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Note 10 - Financial Instruments - Fair Value of Company's Liabilities (Details) - Interest Rate Swap [Member] - USD ($)
Jun. 30, 2018
Dec. 31, 2017
Interest rate swap contracts $ 103,866 $ 246,082
Fair Value, Inputs, Level 1 [Member]    
Interest rate swap contracts
Fair Value, Inputs, Level 2 [Member]    
Interest rate swap contracts 103,866 246,082
Fair Value, Inputs, Level 3 [Member]    
Interest rate swap contracts