Note 2 - Mergers and Acquisitions (Details)					3 Months Ended		9 Months Ended
	Jul. 02, 2018 USD ($)	Jul. 01, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($)	Jun. 29, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Common stock consideration							$ 80,637,194
Total consideration paid							88,970,729
Business Combination, Consideration Transferred							88,970,729
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment					$ 6,091,978		6,091,978
Business Combination, Acquisition Related Costs					1,292,043	$ 407,997	1,798,184	$ 407,997
Post-acquisition compensation, transition and integration costs					493,063	$ 522,740	658,377	$ 522,740
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles					8,208,728		8,208,728
Springfield Bancshares
Number of Branches		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
Share Price | $ / shares				$ 47.45
Total consideration paid		88,970,729		$ 89,000,000
Business Combination, Consideration Transferred		88,970,729		89,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, FHLB and Other Borrowings		83,154,237
Overnight FHLB advances assumed		40,000,000
FHLB term advances assumed		33,610,427
Subordinated debentures		4,743,810
Bank stock loan		4,800,000
Payment of bank stock loan	$ 4,800,000
Nonaccretable Discount, Accelerated					$ 0
Remaining life of loan (in months)					11 months
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		6,091,978
Business Combination, Acquisition Related Costs							1,400,000
Post-acquisition compensation, transition and integration costs					$ 279,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		8,208,728
Proceeds from lines of credit			$ 4,900,000	$ 4,100,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual					7,400,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual					2,200,000
Springfield Bancshares | Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity					$ 10,000,000		$ 10,000,000
Springfield Bancshares | Core Deposits [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		$ 8,208,728
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		10 years
Springfield Bancshares | One Branch Location [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		$ 6,091,978
Write-up of premises and equipment		$ 617,286
Property, Plant and Equipment, Useful Life		39 years