Note 2 - Sales/Mergers/Acquisitions - Springfield Bancshares, Inc (Details)			1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 01, 2018 USD ($) location $ / shares	Jun. 29, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Common stock consideration					$ 81,637,000	$ 30,880,000
Springfield Bancshares
Business Acquisition [Line Items]
Voting interests acquired (as a percent)	100.00%
Number of branches | location	1
Business acquisition exchange ratio	0.3060
Cash per common share | $ / shares	$ 1.50
Share Price | $ / shares		$ 47.45
Common stock consideration	$ 80,637	$ 80,600,000
Line of credit facility, current borrowing capacity		10,000,000
Goodwill, Period Increase				$ 447,000
Other Borrowings | Springfield Bancshares
Business Acquisition [Line Items]
Proceeds from lines of credit		$ 4,100,000	$ 4,900,000