Note 6 - Securities Sold Under Agreements to Repurchase - Securities Sold Under Agreement to Repurchase (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Securities sold under agreements to repurchase	$ 175,850,000	$ 118,365,000
Average daily balance during the period	151,522,000	132,880,000
Maximum daily balance during the period	$ 195,570,000	$ 173,186,000
Securities Sold under Agreements to Repurchase [Member]
Average interest rate at end of period	0.11%	0.12%
Average interest rate during the period	0.11%	0.12%