Note 2 - Mergers and Acquisitions (Details)												3 Months Ended			12 Months Ended
		Feb. 12, 2019	Oct. 01, 2018 USD ($)	Aug. 31, 2018 USD ($)	Jul. 02, 2018 USD ($)	Jul. 01, 2018 USD ($) location $ / shares	Jun. 30, 2018 USD ($)	Jun. 29, 2018 USD ($) $ / shares	Oct. 01, 2017 USD ($) location shares	Sep. 27, 2017 USD ($)	Aug. 31, 2016 USD ($) location	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 29, 2017 $ / shares	Dec. 31, 2015 USD ($)
Cash paid	[1]														$ 9,833,535	$ 7,803,420	$ 80,000,000
Common stock consideration															81,637,166	30,879,485
Goodwill												$ 77,831,902			77,831,902	28,334,092	13,110,913		$ 3,222,688
Total consideration paid															94,970,701	38,682,905	80,000,000
Advances from FHLB												266,492,039			266,492,039
Debt Instrument, Face Amount												40,210,000			40,210,000	40,210,000
Interest rate (as a percent)		5.375%
Premises and equipment, net												6,091,978			6,091,978	4,808,343	20,684,880
Business acquisition related costs															1,795,119	1,068,918	1,400,004
Post-acquisition compensation, transition and integration costs															2,086,386	4,309,565	1,041,169
Intangibles												10,063,660			10,063,660	2,698,301	6,352,653
Total assets acquired												578,913,766			$ 578,913,766	259,590,468	581,676,478
Notes payable																	30,000,000
PCI Loans
Remaining life of loan (in months)															8 months
London Interbank Offered Rate (LIBOR)
Variable interest rate (as a percent)		282.00%
Revolving line of credit
Proceeds from lines of credit																	5,000,000
Line of credit facility, maximum borrowing capacity												10,000,000			$ 10,000,000		10,000,000
Revolving line of credit | London Interbank Offered Rate (LIBOR)
Variable interest rate (as a percent)															2.50%
Guaranty Bank and Trust Company [Member]
Cash paid									$ 7,803,420
Number of branches | location									5
Repayment period (in years)										4 years
Voting interests acquired (as a percent)									100.00%
Common stock consideration									$ 30,879,485
Number of shares expecting to issue based on 10-day volume weighted average of the closing stock price of the Company ending five days prior to closing | shares									678,670
Percentage of total consideration consisting of common stock									79.00%
Percentage of total consideration paid in cash									21.00%
Share Price | $ / shares																		$ 45.50
Goodwill									$ 15,223,179
Total consideration paid									$ 38,682,905
Issuance of shares of common stock as a result of the acquisition, net of issuance cost																30,741,414
Debt Instrument, Face Amount										$ 7,000,000
Term over which goodwill is deductible for tax purposes									15 years
Premises and equipment, net									$ 4,808,343
Business acquisition related costs																805,000,000
Post-acquisition compensation, transition and integration costs																3,100,000
Intangibles									2,698,301
Total assets acquired									$ 259,590,468
Guaranty Bank and Trust Company [Member] | PCI Loans
Nonaccretable discount recognized															$ 137,000	158,000
Guaranty Bank and Trust Company [Member] | Core Deposits [Member]
Acquired finite-lived intangible assets, weighted average useful life									10 years
Guaranty Bank and Trust Company [Member] | Five Branch Locations [Member]
Property, plant and equipment, usefulllife									39 years
Guaranty Bank and Trust Company [Member] | Ten Branch Locations [Member]
Intangibles									$ 4,600,000
Community State Bank [Member]
Cash paid											$ 80,000,000				69,905,355
Number of branches | location											10
Voting interests acquired (as a percent)											100.00%
Goodwill											$ 9,888,225
Total consideration paid											80,000,000
Premises and equipment, net											20,684,880	20,700,000			20,700,000
Business acquisition related costs																473,000	1,400,000
Post-acquisition compensation, transition and integration costs															1,200,000		1,000,000
Intangibles											6,352,653
Stock issued during period (in shares) | shares														1,215,000
Shares issued, price per share | $ / shares														$ 24.75
Proceeds from issuance of common stock, net														$ 29,800,000
Total assets acquired											581,676,478
Revenue of acquiree since acquisition date																	11,400,000
Earnings of acquiree since acquisition date																	2,100,000
Community State Bank [Member] | PCI Loans
Nonaccretable discount recognized															25,000	$ 198,000	186,000
Community State Bank [Member] | QCBT And CRBT [Member]
Cash dividends																	$ 15,200,000
Community State Bank [Member] | Core Deposits [Member]
Intangibles				$ 6,400,000
Community State Bank [Member] | Ten Branch Locations [Member]
Premises and equipment, net				$ 19,700,000
Property, plant and equipment, usefulllife				39 years
Premises and equipment write-up				$ 8,300,000
Community State Bank [Member] | Other Assets [Member]
Total assets acquired											$ 581,000,000
Springfield Bancshares
Cash paid						$ 8,333,535									3,747,209
Number of branches | location						1
Business acquisition exchange ratio						0.3060
Cash per common share | $ / shares						$ 1.50
Voting interests acquired (as a percent)						100.00%
Common stock consideration						$ 80,637,194		$ 80,600,000
Line of credit												9,000,000			9,000,000
Share Price | $ / shares								$ 47.45
Goodwill						45,974,931
Goodwill, Period Increase												447,000
Total consideration paid						88,970,729
Issuance of shares of common stock as a result of the acquisition, net of issuance cost															80,530,957
Payment of bank stock loan					$ 4,800,000
Premises and equipment, net						6,091,978
Business acquisition related costs												391,000	$ 391,000		1,400,000
Intangibles						8,208,728
Line of credit facility, maximum borrowing capacity								$ 10,000,000
Total assets acquired						576,210,340
Revenue of acquiree since acquisition date												15,200,000	15,200,000
Earnings of acquiree since acquisition date												4,800,000	$ 4,800,000
Springfield Bancshares | Core Deposits [Member]
Intangibles						$ 8,200,000
Acquired finite-lived intangible assets, weighted average useful life						10 years
Springfield Bancshares | Ten Branch Locations [Member]
Property, plant and equipment, usefulllife						39 years
Springfield Bancshares | Other Borrowings
Proceeds from lines of credit							$ 4,900,000	$ 4,100,000
Bates Companies [Member]
Assets under management			$ 704,000,000
Cash consideration paid from operating cash			1,500,000
Cash paid			$ 3,000,000												$ 1,435,595
Voting interests acquired (as a percent)			100.00%
Number of shares expecting to issue based on 10-day volume weighted average of the closing stock price of the Company ending five days prior to closing | shares															47,003
Stock consideration												3,000,000			$ 3,000,000
Goodwill												3,766,074			3,766,074
Issuance of shares of common stock as a result of the acquisition, net of issuance cost															999,972
Business acquisition related costs															$ 394,000
Stock issued during period (in shares) | shares															23,501
Bates Companies [Member] | Promissory Note [Member]
Frequency of installments			annual installments
Repayment period (in years)			5 years
Periodic payment of principal amount			$ 300,000
Interest rate (as a percent)			2.18%
Bates Companies [Member] | Customer Lists [Member]
Intangibles												1,854,932			$ 1,854,932
Bates Companies [Member] | Other Liabilities.
Business combination, contingent consideration												$ 2,000,000			$ 2,000,000
Bates Companies [Member] | Other Liabilities. | Promissory Note [Member]
Promissory note			$ 1,500,000
Maximum | Bates Companies [Member]
Common stock consideration			$ 3,000,000

[1] Net cash paid at closing totaled $1,435,595 for acquisition of the Bates Companies in 2018. Net cash paid at closing totaled $3,747,209 for merger with Springfield Bancshares in 2018. Net cash paid at closing totaled $3,368,909 for acquisition of Guaranty Bank in 2017. Net cash paid at closing totaled $69,905,355 for acquisition of CSB in 2016.