Note 3 - Investment Securities Available for Sale - Amortized Cost and Estimated Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Investment securities available for sale, amortized cost	$ 477,613	$ 535,269
Investment securities available for sale, gross unrealized gains	5,033	1,883
Investment securities available for sale, gross unrealized losses	(25,926)	(47,971)
Estimated fair value	456,720	489,181
US Treasury Securities [Member]
Investment securities available for sale, amortized cost	3,998	6,978
Investment securities available for sale, gross unrealized gains	0	0
Investment securities available for sale, gross unrealized losses	(7)	(98)
Estimated fair value	3,991	6,880
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, amortized cost	243,643	256,694
Investment securities available for sale, gross unrealized gains	2,287	351
Investment securities available for sale, gross unrealized losses	(10,244)	(21,114)
Estimated fair value	235,686	235,931
Commercial Mortgage Backed Securities Issued by US Government Agencies [Member]
Investment securities available for sale, amortized cost	134,642	129,321
Investment securities available for sale, gross unrealized gains	1,609	465
Investment securities available for sale, gross unrealized losses	(8,867)	(13,834)
Estimated fair value	127,384	115,952
US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, amortized cost	95,330	142,276
Investment securities available for sale, gross unrealized gains	1,137	1,067
Investment securities available for sale, gross unrealized losses	(6,808)	(12,925)
Estimated fair value	$ 89,659	$ 130,418