Note 2 - Investment Securities - Securities by Contractual Maturity (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Securities held to maturity, due in one year or less, amortized cost	$ 3,344,356
Securities held to maturity, due in one year or less, fair value	3,345,990
Securities held to maturity, due after one year through five years, amortized cost	25,163,524
Securities held to maturity, due after one year through five years, fair value	25,191,668
Securities held to maturity, due after five years, amortized cost	350,076,457
Securities held to maturity, due after five years, fair value	347,255,025
Securities held to maturity, amortized cost	378,584,337
Securities held to maturity, fair value	375,792,683	$ 379,749,804
Securities available for sale, due in one year or less, amortized cost	3,368,633
Securities available for sale, Due in one year or less, fair value	3,381,748
Securities available for sale, due after one year through five years, amortized cost	23,949,100
Securities available for sale, Due after one year through five years, fair value	23,738,028
Securities available for sale, due after five years, amortized cost	76,390,803
Securities available for sale, Due after five years, fair value	75,236,121
Securities available for sale, single maturity, amortized cost	103,708,536
Securities available for sale, single maturity, fair value	102,355,897
Securities available for sale, amortized cost	266,162,141
Securities available for sale, fair value	259,644,940
Callable Securities [Member]
Securities available for sale, amortized cost	59,065,640
Securities available for sale, fair value	58,206,494
US States and Political Subdivisions Debt Securities [Member]
Securities held to maturity, fair value	374,753,858	$ 378,699,804
US States and Political Subdivisions Debt Securities [Member] | Callable Securities [Member]
Securities available for sale, no single maturity, amortized cost	54,016,828
Securities available for sale, no single maturity, fair value	53,258,850
Securities available for sale, callable, amortized cost	54,016,828
Securities available for sale, callable, fair value	53,258,850
US Government Agencies Debt Securities [Member] | Callable Securities [Member]
Securities available for sale, no single maturity, amortized cost	5,048,812
Securities available for sale, no single maturity, fair value	4,947,644
Securities available for sale, callable, amortized cost	5,048,812
Securities available for sale, callable, fair value	4,947,644
Residential Mortgage Backed Securities [Member]
Securities available for sale, no single maturity, amortized cost	162,453,605
Securities available for sale, no single maturity, fair value	157,289,043
Securities available for sale, callable, amortized cost	162,453,605
Securities available for sale, callable, fair value	157,289,043
Callable Securities [Member] | US States and Political Subdivisions Debt Securities [Member]
Securities held to maturity, callable, amortized cost	209,306,946
Securities held to maturity, callable, fair value	$ 207,262,788