Note 3 - Investment Securities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) item security	Dec. 31, 2020 USD ($) item	Dec. 31, 2019 USD ($)
Number of securities | security	622
Available-for-sale, unrealized loss positions, qualitative disclosure, number of positions | security	42
Aggregate losses of securities (as a percent)	0.17%
Available-for-sale, unrealized loss positions, qualitative disclosure, number of positions, greater than or equal to one year | security	13
Sale of securities | $	$ 23,874	$ 38,562	$ 30,055
Gain on sale | $		2,553	$ 176
Security Owned and Pledged as Collateral, Fair Value | $	$ 246,500	$ 212,800
Number Of Charters Owning Municipal Securities	4
Revenue Bonds
Number of issuers	2
Percentage threshold	5.00%	5.00%
Municipal securities | General Obligation Bonds
Number of issuers	113	117
Other investments | $	$ 114,500	$ 116,700
Number of states holding investments	20	21
Municipal securities | General Obligation Bonds | Minimum
Other investments | $	$ 5,000	$ 5,000
Municipal securities | General Obligation Bonds | Aggregate Fair Value Exceeding 5 Million [Member]
Number of states holding investments	7	8
Municipal securities | Revenue Bonds
Number of issuers	165	191
Other investments | $	$ 575,000	$ 555,900
Number of states holding investments	25	26
Municipal securities | Revenue Bonds | Minimum
Other investments | $	$ 5,000	$ 5,000
Municipal securities | Revenue Bonds | Aggregate Fair Value Exceeding 5 Million [Member]
Number of states holding investments	13	12