Note 2 - Investment Securities - Securities by Contractual Maturity (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Securities HTM:
Securities held to maturity, due in one year or less, amortized cost	$ 2,940,492
Securities held to maturity, due in one year or less, fair value	2,940,378
Securities held to maturity, due after one year through five years, amortized cost	18,268,264
Securities held to maturity, due after one year through five years, fair value	18,374,059
Securities held to maturity, due after five years, amortized cost	302,772,471
Securities held to maturity, due after five years, fair value	302,122,141
Securities held to maturity, amortized cost	323,981,227
Securities held to maturity, fair value	323,436,578	$ 320,414,899
Securities AFS:
Securities available for sale, due in one year or less, amortized cost	3,135,008
Securities available for sale, Due in one year or less, fair value	3,143,223
Securities available for sale, due after one year through five years, amortized cost	26,545,903
Securities available for sale, Due after one year through five years, fair value	26,712,930
Securities available for sale, due after five years, amortized cost	66,280,807
Securities available for sale, Due after five years, fair value	66,247,075
Securities available for sale, single maturity, amortized cost	95,961,718
Securities available for sale, single maturity, fair value	96,103,228
Securities available for sale, amortized cost	260,367,974
Securities available for sale, fair value	259,954,422
Securities available for sale, callable, amortized cost	260,367,974
Callable Securities [Member]
Securities AFS:
Securities available for sale, amortized cost	50,775,656
Securities available for sale, fair value	50,673,922
Securities available for sale, callable, amortized cost	50,775,656
US States and Political Subdivisions Debt Securities [Member]
Securities HTM:
Securities held to maturity, fair value	322,386,578	319,364,899
US States and Political Subdivisions Debt Securities [Member] | Callable Securities [Member]
Securities AFS:
Securities available for sale, no single maturity, amortized cost	45,727,004
Securities available for sale, no single maturity, fair value	45,640,630
Securities available for sale, callable, amortized cost	45,727,004
Securities available for sale, callable, fair value	45,640,630
US Government-sponsored Enterprises Debt Securities [Member] | Callable Securities [Member]
Securities AFS:
Securities available for sale, no single maturity, amortized cost	5,048,652
Securities available for sale, no single maturity, fair value	5,033,292
Securities available for sale, callable, amortized cost	5,048,652
Securities available for sale, callable, fair value	5,033,292
Residential Mortgage Backed Securities [Member]
Securities AFS:
Securities available for sale, no single maturity, amortized cost	160,329,128
Securities available for sale, no single maturity, fair value	158,968,509
Securities available for sale, callable, amortized cost	160,329,128
Securities available for sale, callable, fair value	158,968,509
Other Securities [Member]
Securities HTM:
Securities held to maturity, fair value	1,050,000	$ 1,050,000
Securities AFS:
Securities available for sale, no single maturity, amortized cost	4,077,128
Securities available for sale, no single maturity, fair value	4,882,685
Securities available for sale, callable, amortized cost	4,077,128
Securities available for sale, callable, fair value	4,882,685
Callable Securities [Member] | US States and Political Subdivisions Debt Securities [Member]
Securities HTM:
Securities held to maturity, callable, amortized cost	170,900,193
Securities held to maturity, callable, fair value	$ 171,633,005