Note 6 - Income Per Common Share - Income Per Share (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Basic Income Per Common Share, Income Available to Common Shareholders	$ 1,355,745	$ 1,429,241
Basic Income Per Common Share, Average Common Shares Outstanding (in shares)	4,391,717	4,363,071
Basic Income Per Common Share (in dollars per share)	$ 0.31	$ 0.33
Effect of Dilutive Securities, Average Common Shares Outstanding (in shares)	75,069	56,952
Diluted Income Per Common Share, Income Available to Common Shareholders	$ 1,355,745	$ 1,429,241
Diluted Income Per Common Share, Average Common Shares Outstanding (in shares)	4,466,786	4,420,023
Diluted Income Per Common Share (in dollars per share)	$ 0.30	$ 0.32