Note 3 - Investment Securities - Securities in a Continuous Unrealized Loss Position (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Securities held to maturity:
Securities held to maturity, less than 12 months, fair value	$ 171,170,164
Securities held to maturity, less than 12 months, gross unrealized losses	(5,453,001)
Securities held to maturity, 12 months or more, fair value	64,984,249
Securities held to maturity, 12 months or more, gross unrealized losses	(5,314,336)
Securities held to maturity, fair value	236,154,413
Securities held to maturity, gross unrealized losses	(10,767,337)
Securities available for sale:
Securities available for sale, less than 12 months, fair value	146,978,402	$ 128,656,909
Securities available for sale, less than 12 months, gross unrealized losses	(3,269,921)	(1,138,843)
Securities available for sale, 12 months or more, fair value	131,789,243	71,569,641
Securities available for sale, 12 months or more, gross unrealized losses	(6,608,419)	(1,761,568)
Securities available for sale, fair value	278,767,645	200,226,550
Securities available for sale, gross unrealized losses	(9,878,340)	(2,900,411)
US States and Political Subdivisions Debt Securities [Member]
Securities held to maturity:
Securities held to maturity, less than 12 months, fair value	170,633,644	23,750,826
Securities held to maturity, less than 12 months, gross unrealized losses	(5,439,521)	(354,460)
Securities held to maturity, 12 months or more, fair value	64,984,249	72,611,780
Securities held to maturity, 12 months or more, gross unrealized losses	(5,314,336)	(2,133,659)
Securities held to maturity, fair value	235,617,893	96,362,606
Securities held to maturity, gross unrealized losses	(10,753,857)	(2,488,119)
Securities available for sale:
Securities available for sale, less than 12 months, fair value	79,442,346	10,229,337
Securities available for sale, less than 12 months, gross unrealized losses	(976,811)	(41,151)
Securities available for sale, 12 months or more, fair value	10,952,533	9,997,433
Securities available for sale, 12 months or more, gross unrealized losses	(371,217)	(169,949)
Securities available for sale, fair value	90,394,879	20,226,770
Securities available for sale, gross unrealized losses	(1,348,028)	(211,100)
US Government Agencies Debt Securities [Member]
Securities available for sale:
Securities available for sale, less than 12 months, fair value	18,437,573	28,576,258
Securities available for sale, less than 12 months, gross unrealized losses	(521,633)	(200,022)
Securities available for sale, 12 months or more, fair value	15,829,173	3,640,477
Securities available for sale, 12 months or more, gross unrealized losses	(712,383)	(149,945)
Securities available for sale, fair value	34,266,746	32,216,735
Securities available for sale, gross unrealized losses	(1,234,016)	(349,967)
Residential Mortgage Backed Securities [Member]
Securities available for sale:
Securities available for sale, less than 12 months, fair value	44,903,593	88,927,779
Securities available for sale, less than 12 months, gross unrealized losses	(1,712,003)	(871,855)
Securities available for sale, 12 months or more, fair value	105,007,537	57,931,731
Securities available for sale, 12 months or more, gross unrealized losses	(5,524,819)	(1,441,674)
Securities available for sale, fair value	149,911,130	146,859,510
Securities available for sale, gross unrealized losses	(7,236,822)	(2,313,529)
Other Securities [Member]
Securities held to maturity:
Securities held to maturity, less than 12 months, fair value	536,520
Securities held to maturity, less than 12 months, gross unrealized losses	(13,480)
Securities held to maturity, fair value	536,520
Securities held to maturity, gross unrealized losses	(13,480)
Securities available for sale:
Securities available for sale, less than 12 months, fair value	4,194,890	923,535
Securities available for sale, less than 12 months, gross unrealized losses	(59,474)	(25,815)
Securities available for sale, fair value	4,194,890	923,535
Securities available for sale, gross unrealized losses	$ (59,474)	$ (25,815)

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

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