Note 3 - Investment Securities - Activity in Allowance for Credit Losses (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Provision for credit loss expense	$ 15
Balance, ending	198
Accounting Standards Update 2016-13
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Balance, ending	183
Municipal securities.
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Provision for credit loss expense	16
Balance, ending	198
Municipal securities. | Accounting Standards Update 2016-13
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Balance, ending	182
Other Securities
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Provision for credit loss expense	(1)
Other Securities | Accounting Standards Update 2016-13
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Balance, ending	$ 1