Note 16 - Quarterly Results of Operations - Summary of Quarterly Results (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Total income	$ 4,599,891	$ 4,525,190	$ 4,385,506	$ 4,257,746	$ 4,264,414	$ 4,232,017	$ 4,121,760	$ 3,976,612	$ 17,768,333	$ 16,594,803
Interest expense	726,549	664,018	580,913	535,761	466,104	442,805	412,618	385,713	2,507,241	1,707,240
Net interest income	3,873,342	3,861,172	3,804,593	3,721,985	3,798,310	3,789,212	3,709,142	3,590,899	15,261,092	14,887,563
Provision for loan losses	450,000	(100,000)	75,000	50,000	60,000	225,000	75,000	50,000	475,000	410,000
	$ 1,136,805	$ 1,308,688	$ 1,145,065	$ 1,122,118	$ 656,339	$ 1,014,456	$ 1,134,889	$ 983,557	$ 4,712,676	$ 3,789,241
Earnings per share - basic and diluted (in dollars per share)	$ 0.68	$ 0.78	$ 0.69	$ 0.67	$ 0.39	$ 0.61	$ 0.69	$ 0.59	$ 2.82	$ 2.28