Note 9 - Securities Sold Under Agreements to Repurchase - Securities Sold Under Agreement to Repurchase (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Outstanding balance at year-end	$ 102,675,000	$ 103,519,000
Average daily balance during the year	105,234,000	101,005,000
Maximum daily balance during the year	$ 133,411,000	$ 123,046,000
Securities Sold under Agreements to Repurchase [Member]
Weighted average interest rate at year-end	0.17%	0.26%
Weighted average interest rate during the year	0.24%	0.24%