Note 3 - Investment Securities - Securities by Contractual Maturity (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Securities held to maturity:
Securities held to maturity, due in one year or less, amortized cost	$ 2,232,726
Securities held to maturity, due in one year or less, fair value	2,237,767
Securities held to maturity, due after one year through five years, amortized cost	27,569,566
Securities held to maturity, due after one year through five years, fair value	27,716,775
Securities held to maturity, due after five years, amortized cost	372,110,593
Securities held to maturity, due after five years, fair value	370,816,041
Securities held to maturity, amortized cost	401,912,885
Securities held to maturity, fair value	400,770,583	$ 379,749,804
Securities available for sale:
Securities available for sale, due in one year or less, amortized cost	2,665,560
Securities available for sale, Due in one year or less, fair value	2,665,829
Securities available for sale, due after one year through five years, amortized cost	29,140,442
Securities available for sale, Due after one year through five years, fair value	28,856,751
Securities available for sale, due after five years, amortized cost	71,167,855
Securities available for sale, Due after five years, fair value	70,284,608
Securities available for sale, single maturity, amortized cost	102,973,857
Securities available for sale, single maturity, fair value	101,807,188
Securities available for sale, amortized cost	266,671,830
Securities available for sale, fair value	261,056,448
Callable Securities [Member]
Securities available for sale:
Securities available for sale, amortized cost	61,220,638
Securities available for sale, fair value	60,631,128
US States and Political Subdivisions Debt Securities
Securities held to maturity:
Securities held to maturity, fair value	399,721,215	378,699,804
US States and Political Subdivisions Debt Securities | Callable Securities [Member]
Securities available for sale:
Securities available for sale, no single maturity, amortized cost	49,715,648
Securities available for sale, no single maturity, fair value	49,110,178
Securities available for sale, callable, amortized cost	49,715,648
Securities available for sale, callable, fair value	49,110,178
U.S. govt. sponsored agency securities | Callable Securities [Member]
Securities available for sale:
Securities available for sale, no single maturity, amortized cost	4,999,072
Securities available for sale, no single maturity, fair value	4,918,050
Securities available for sale, callable, amortized cost	4,999,072
Securities available for sale, callable, fair value	4,918,050
Residential Mortgage Backed Securities
Securities available for sale:
Securities available for sale, no single maturity, amortized cost	163,697,973
Securities available for sale, no single maturity, fair value	159,249,260
Securities available for sale, callable, amortized cost	163,697,973
Securities available for sale, callable, fair value	159,249,260
Other Securities
Securities held to maturity:
Securities held to maturity, fair value	1,049,368	$ 1,050,000
Other Securities | Callable Securities [Member]
Securities available for sale:
Securities available for sale, no single maturity, amortized cost	6,505,918
Securities available for sale, no single maturity, fair value	6,602,900
Securities available for sale, callable, amortized cost	6,505,918
Securities available for sale, callable, fair value	6,602,900
Callable Securities [Member] | US States and Political Subdivisions Debt Securities
Securities held to maturity:
Securities held to maturity, callable, amortized cost	209,953,250
Securities held to maturity, callable, fair value	$ 208,366,466