Note 20 - Unaudited Quarterly Operating Results - Quarterly Financial Data (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income	$ 7,902,636	$ 7,525,187	$ 7,241,508	$ 6,771,402	$ 6,625,664	$ 6,354,303	$ 6,204,314	$ 6,205,045	$ 29,440,733	$ 25,389,326	$ 25,189,634
Interest expense	2,087,594	1,473,190	1,352,309	1,173,461	1,068,638	1,056,181	1,026,782	1,025,411	6,086,554	4,177,012	4,279,882
Net interest income	5,815,042	6,051,997	5,889,199	5,597,941	5,557,026	5,298,122	5,177,532	5,179,634	23,354,179	21,212,314	20,909,752
Provision for loan losses	250,000	450,000	575,000	475,000	425,000	200,000	375,000	375,000	1,750,000	1,375,000	600,000
Gain on loans and investment securities	705,583	858,826	710,665	539,102	544,172	658,205	525,644	470,456
Other noninterest income, net	854,443	712,043	656,395	690,263	722,299	657,296	653,769	638,366
Noninterest expense	5,603,718	5,011,832	4,567,916	4,419,620	4,364,169	4,317,707	4,309,394	4,109,476	19,603,086	17,100,746	16,609,728
Income before income taxes	1,521,350	2,161,034	2,113,343	1,932,686	2,034,328	2,095,916	1,672,551	1,803,980	7,728,413	7,606,775	8,178,096
Provision for income taxes	1,102,883	443,651	520,770	503,445	514,981	554,009	416,399	527,375	2,570,749	2,012,764	2,461,329
Net income available to common shareholders	$ 418,467	$ 1,717,383	$ 1,592,573	$ 1,429,241	$ 1,519,347	$ 1,541,907	$ 1,256,152	$ 1,276,605	$ 5,157,664	$ 5,594,011	$ 5,716,767
Basic income per common share (in dollars per share)	$ 0.10	$ 0.39	$ 0.36	$ 0.33	$ 0.35	$ 0.35	$ 0.29	$ 0.29	$ 1.18	$ 1.28	$ 1.32
Diluted income per common share (in dollars per share)	$ 0.09	$ 0.39	$ 0.36	$ 0.32	$ 0.34	$ 0.35	$ 0.28	$ 0.29	$ 1.16	$ 1.27	$ 1.30