Note 5 - Debt Securities - Debt Securities Held to Maturity by Credit Rating (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt securities held to maturity (at amortized cost; estimated fair value - $86,627 - 2022, $101,242 - 2021)	$ 96,163	$ 98,060
Standard & Poor's, AAA Rating [Member]
Debt securities held to maturity (at amortized cost; estimated fair value - $86,627 - 2022, $101,242 - 2021)	12,846	15,450
Standard & Poor's, AA Rating [Member]
Debt securities held to maturity (at amortized cost; estimated fair value - $86,627 - 2022, $101,242 - 2021)	75,932	75,119
Standard & Poor's, A Rating [Member]
Debt securities held to maturity (at amortized cost; estimated fair value - $86,627 - 2022, $101,242 - 2021)	7,385	7,491
Standard & Poor's, BBB Rating [Member]
Debt securities held to maturity (at amortized cost; estimated fair value - $86,627 - 2022, $101,242 - 2021)	0	0
Standard Poors Below Investment Grade Rating [Member]
Debt securities held to maturity (at amortized cost; estimated fair value - $86,627 - 2022, $101,242 - 2021)	$ 0	$ 0