Note 6 - Short-term Borrowings - Federal Funds Purchased and Short-term Borrowings (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Balance at Period End, Amount	$ 34,967	$ 30,571
Other Short-term Debt [Member]
Balance at Period End, Amount	$ 34,967	$ 30,571
Balance at Period End, Weighted Average Rate	0.57%	0.57%
Federal Funds Purchased [Member]
Average Balance Outstanding During the Period, Amount	$ 29,539	$ 29,976
Average Balance Outstanding During the Period, Weighted Average Rate	0.61%	0.62%
Maximum Amount Outstanding at any Month End, Amount	$ 34,967	$ 34,197
Securities Sold under Agreements to Repurchase [Member]
Carrying Value, Amount	36,168	37,584
Market Value, Amount	$ 37,475	$ 37,873