Note 6 - Income Per Common Share - Income Per Share (Details) - USD ($)	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Basic Income Per Common Share, Income Available to Common Shareholders	$ 1,717,383	$ 1,541,907	$ 1,541,907	$ 4,074,664	$ 4,739,197	$ 4,074,664
Basic Income Per Common Share, Average Common Shares Outstanding (in shares)	4,374,725	4,370,700		4,365,835	4,370,877
Basic Income Per Common Share (in dollars per share)	$ 0.39	$ 0.35	$ 0.35	$ 0.93	$ 1.08	$ 0.93
Effect of Dilutive Securities, Average Common Shares Outstanding (in shares)	72,841	56,853		53,553	64,815
Diluted Income Per Common Share, Income Available to Common Shareholders	$ 1,717,383	$ 1,541,907		$ 4,074,664	$ 4,739,197
Diluted Income Per Common Share, Average Common Shares Outstanding (in shares)	4,447,566	4,427,553		4,419,388	4,435,692
Diluted Income Per Common Share (in dollars per share)	$ 0.39	$ 0.35	$ 0.35	$ 0.92	$ 1.07	$ 0.92