Note 2 - Acquisitions (Details Textual)					3 Months Ended	6 Months Ended	12 Months Ended
		Oct. 01, 2017 USD ($) shares	Sep. 27, 2017 USD ($)	Aug. 31, 2016 USD ($)	Jun. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 29, 2017 $ / shares
Number of Branches				10
Payments to Acquire Businesses, Gross	[1]						$ 7,803,420	$ 80,000,000
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable							30,879,485
Business Combination, Consideration Transferred							38,682,905	80,000,000
Debt Instrument, Face Amount						$ 35,570,000	40,210,000	35,570,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment						20,684,880	4,808,343	20,684,880
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles						6,352,653	2,698,301	6,352,653
Business Combination, Acquisition Related Costs							1,068,918	1,400,004
Business Combination, Integration Related Costs							4,309,565	1,041,169
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets				$ 581,000,000		581,676,478	259,590,468	581,676,478
Stock Issued During Period, Shares, New Issues | shares					1,215,000
Shares Issued, Price Per Share | $ / shares					$ 24.75
Proceeds from Issuance of Common Stock					$ 29,800,000
Notes Payable						30,000,000		30,000,000
Revolving Credit Facility [Member]
Proceeds from Lines of Credit								5,000,000
Line of Credit Facility, Maximum Borrowing Capacity						10,000,000	10,000,000	10,000,000
Guaranty Bank and Trust Company [Member]
Number of Branches		5
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Business Acquisition, Equity Interest Issued or Issuable, Percentage of Aggregate Consideration		79.00%
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares		678,670
Payments to Acquire Businesses, Gross, Percentage of Aggregate Consideration		21.00%
Payments to Acquire Businesses, Gross		$ 7,803,420
Share Price | $ / shares										$ 45.50
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable		30,879,485
Business Combination, Consideration Transferred		$ 38,682,905
Debt Instrument, Face Amount			$ 7,000,000
Debt Instrument, Term			4 years
Business Acquisition, Goodwill, Expected Tax Deductible Amount, Term		15 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		$ 4,808,343
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		2,698,301
Business Combination, Acquisition Related Costs							1,100,000
Business Combination, Integration Related Costs							3,100,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		259,590,468
Guaranty Bank and Trust Company [Member] | Core Deposits [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		$ 2,698,301
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		10 years
Guaranty Bank and Trust Company [Member] | Five Branch Locations [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		$ 4,614,604
Impairment of Long-Lived Assets Held-for-use		$ 998,343
Property, Plant and Equipment, Useful Life		39 years
Guaranty Bank and Trust Company [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Nonaccretable Discount, Accelerated							158,000
Guaranty Bank and Trust Company [Member] | Other Assets [Member]
Assets Held-for-sale, Not Part of Disposal Group							3,600,000
Community State Bank [Member]
Business Acquisition, Percentage of Voting Interests Acquired				100.00%
Payments to Acquire Businesses, Gross				$ 80,000,000
Business Combination, Consideration Transferred				80,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment				20,684,880
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles				6,352,653
Business Combination, Acquisition Related Costs						473,000		1,400,000
Business Combination, Integration Related Costs							1,200,000	1,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets				581,676,478
Dividends, Cash								15,200,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual						11,400,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual						$ 2,100,000
Community State Bank [Member] | Core Deposits [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles				$ 6,352,653
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				10 years
Community State Bank [Member] | Ten Branch Locations [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment				$ 19,735,000
Property, Plant and Equipment, Useful Life				39 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment, Write-up				$ 8,334,437
Community State Bank [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Nonaccretable Discount, Accelerated							$ 198,000	$ 186,000

[1] Net cash paid at closing totaled $69,905,355 for acquisition of CSB in 2016.