Note 4 - Securities - Available-for-sale Securities by Maturity (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
1-5 years, amortized cost	$ 1,151,319
1-5 years, fair value	1,149,719
5-10 years, amortized cost	42,499,397
5-10 years, fair value	43,180,499
After 10 years, amortized cost	44,862,785
After 10 years, fair value	46,822,831
Available-for-sale securities, amortized cost	148,001,599	$ 117,152,760
Available-for-sale securities	152,236,508	118,245,314
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Not due on a single maturity date, amortized cost	13,145,778
Not due on a single maturity date, fair value	13,331,303
Available-for-sale securities, amortized cost	13,145,778	13,788,728
Available-for-sale securities	13,331,303	13,811,371
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Not due on a single maturity date, amortized cost	46,342,320
Not due on a single maturity date, fair value	47,752,156
Available-for-sale securities, amortized cost	46,342,320	49,844,049
Available-for-sale securities	$ 47,752,156	$ 50,236,236