Note 2 - Sales/Mergers/Acquisitions - Springfield Bancshares, Inc (Details) $ / shares in Units, $ in Thousands				3 Months Ended	12 Months Ended
	Jul. 01, 2018 USD ($) location $ / shares	Jun. 30, 2018 USD ($)	Jun. 29, 2018 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Common stock consideration					$ 81,637
Total consideration paid					$ 94,971
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
Total consideration paid	$ 88,971		89,000
Line of credit facility, current borrowing capacity			10,000
Goodwill, Period Increase				$ 447
Other Borrowings | Springfield Bancshares
Business Acquisition [Line Items]
Proceeds from lines of credit		$ 4,900	$ 4,100