Note 4 - Securities - Available-for-sale Securities by Maturity (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
1-5 years, amortized cost	$ 150,000
1-5 years, fair value	150,243
5-10 years, amortized cost	25,335,491
5-10 years, fair value	25,396,479
After 10 years, amortized cost	42,350,022
After 10 years, fair value	43,557,642
Available-for-sale securities, amortized cost	137,926,282	$ 117,152,760
Available-for-sale securities	140,009,454	118,245,314
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Not due on a single maturity date, amortized cost	14,239,775
Not due on a single maturity date, fair value	13,560,632
Available-for-sale securities, amortized cost	14,239,775	13,788,728
Available-for-sale securities	13,560,632	13,811,371
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Not due on a single maturity date, amortized cost	55,850,994
Not due on a single maturity date, fair value	57,344,458
Available-for-sale securities, amortized cost	55,850,994	49,844,049
Available-for-sale securities	$ 57,344,458	$ 50,236,236

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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