Note 4 - Investment Securities - Summary of Amortized Cost and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Held-to-maturity securities (fair value of $194,251 in 2023; $187,280 in 2022)	$ 223,112	$ 222,744
Held to maturity securities, gross unrealized gains	0	0
Held to maturity securities, gross unrealized losses	(28,861)	(35,464)
Held to maturity securities, fair value	194,251	187,280
Available for sale securities, amortized cost	449,468	488,741
Available for sale debt securities, gross unrealized gains	5	501
Available for sale securities, gross unrealized losses	(58,059)	(68,380)
Available for sale debt security, fair value	391,414	420,862
US Government Agencies Debt Securities [Member]
Held-to-maturity securities (fair value of $194,251 in 2023; $187,280 in 2022)	80,572	80,306
Held to maturity securities, gross unrealized gains	0	0
Held to maturity securities, gross unrealized losses	(7,726)	(9,243)
Held to maturity securities, fair value	72,846	71,063
Available for sale securities, amortized cost	31,108	36,076
Available for sale debt securities, gross unrealized gains	0	0
Available for sale securities, gross unrealized losses	(3,958)	(4,543)
Available for sale debt security, fair value	27,150	31,533
US States and Political Subdivisions Debt Securities [Member]
Held-to-maturity securities (fair value of $194,251 in 2023; $187,280 in 2022)	142,540	142,438
Held to maturity securities, gross unrealized gains	0	0
Held to maturity securities, gross unrealized losses	(21,135)	(26,221)
Held to maturity securities, fair value	121,405	116,217
Available for sale securities, amortized cost	174,418	197,935
Available for sale debt securities, gross unrealized gains	5	501
Available for sale securities, gross unrealized losses	(20,634)	(26,542)
Available for sale debt security, fair value	153,789	171,894
Mortgage-Backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available for sale securities, amortized cost	243,942	254,730
Available for sale debt securities, gross unrealized gains	0	0
Available for sale securities, gross unrealized losses	(33,467)	(37,295)
Available for sale debt security, fair value	$ 210,475	$ 217,435

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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