Note 4 - Securities - Available-for-sale Debt Securities (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Available-for-sale securities, amortized cost	$ 148,001,599	$ 117,152,760
Available-for-sale securities, gross unrealized gains	4,508,765	1,468,000
Available-for-sale securities, gross unrealized (losses)	(273,856)	(375,446)
Available-for-sale securities	152,236,508	118,245,314
US Government Agencies Debt Securities [Member]
Available-for-sale securities, amortized cost	7,282,000	2,499,755
Available-for-sale securities, gross unrealized gains	19,524	0
Available-for-sale securities, gross unrealized (losses)	0	(11,962)
Available-for-sale securities	7,301,524	2,487,793
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities, amortized cost	53,659,414	35,625,038
Available-for-sale securities, gross unrealized gains	2,588,022	675,382
Available-for-sale securities, gross unrealized (losses)	(34,637)	(125,693)
Available-for-sale securities	56,212,799	36,174,727
Corporate Debt Securities [Member]
Available-for-sale securities, amortized cost	27,572,087	15,395,190
Available-for-sale securities, gross unrealized gains	213,432	154,942
Available-for-sale securities, gross unrealized (losses)	(146,793)	(14,945)
Available-for-sale securities	27,638,726	15,535,187
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Available-for-sale securities, amortized cost	13,145,778	13,788,728
Available-for-sale securities, gross unrealized gains	237,257	52,035
Available-for-sale securities, gross unrealized (losses)	(51,732)	(29,392)
Available-for-sale securities	13,331,303	13,811,371
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available-for-sale securities, amortized cost	46,342,320	49,844,049
Available-for-sale securities, gross unrealized gains	1,450,530	585,641
Available-for-sale securities, gross unrealized (losses)	(40,694)	(193,454)
Available-for-sale securities	$ 47,752,156	$ 50,236,236