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Note 13 - Federal and State Income Taxes - Reconciliation of the Expected Federal Income Tax Expense (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Computed "expected" tax expense									$ 14,228,535	$ 12,806,351	$ 7,208,993
Effect of graduated tax rates										(250,013)	(76,973)
Tax exempt income, net									(5,653,979)	(4,343,270)	(3,461,438)
Bank-owned life insurance									630,855	619,988	616,737
State income taxes, net of federal benefit, current year									1,764,671	1,245,524	767,557
Change in unrecognized tax benefits									(53,699)	121,008	223,668
New Markets Tax Credits and other credits									(341,268)	(180,000)	(180,000)
Acquisition costs										176,050
Excess tax benefit on stock options exercised and restricted stock awards vested									(1,219,483)
Re-measurement of deferred tax asset to incorporate newly enacted tax rates									(2,918,606)
Other									(228,866)	(52,875)	(195,828)
	$ (2,000,105)	$ 1,921,533	$ 2,635,576	$ 2,389,446	$ 2,872,412	$ 1,858,208	$ 2,153,144	$ 2,019,023	$ 4,946,450	$ 8,902,787	$ 3,669,242
Computed "expected" tax expense, percentage									35.00%	35.00%	35.00%
Effect of graduated tax rates, percentage										(0.70%)	(0.40%)
Tax exempt income, net, percentage									(13.90%)	(11.90%)	(16.80%)
Bank-owned life insurance, percentage									(1.50%)	(1.70%)	(3.00%)
State income taxes, net of federal benefit, current year, percentage									4.30%	3.40%	3.70%
Change in unrecognized tax benefits, percentage									(0.10%)	0.30%	1.10%
New Markets Tax Credits and other credits, percentage									(0.80%)	(0.50%)	(0.90%)
Acquisition costs, percentage										0.50%
Excess tax benefit on stock options exercised and restricted stock awards vested, percentage									(3.00%)
Re-measurement of deferred tax asset to incorporate newly enacted tax rates, percentage									(7.20%)
Other, percentage									(0.60%)	(0.10%)	(0.90%)
Income Tax Expense (Benefit), Pprcentage									12.20%	24.30%	17.80%