Note 6 - Fair Value Measurements and Fair Value of Financial Instruments - Quantitative Information About Significant Unobservable Inputs (Details) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Securities available-for-sale	$ 581,867	$ 634,884
Fair Value, Recurring [Member]
Securities available-for-sale	581,867	634,884
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Securities available-for-sale	7,017	7,349
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale	122,899	142,896
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Recurring [Member]
Securities available-for-sale	122,899	142,896
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Securities available-for-sale	$ 7,017	$ 7,349
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rate [Member]
Securities available-for-sale, rate	0.044	0.043