Note 3 - Investment Securities Available for Sale - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Within one year, amortized cost	$ 7,943
Within one year, estimated fair value	7,866
After one year through five years, amortized cost	5,493
After one year through five years, estimated fair value	5,399
After five years through ten years, amortized cost	14,418
After five years through ten years, estimated fair value	14,299
After ten years, amortized cost	74,452
After ten years, estimated fair value	67,170
Amortized Cost	480,686	$ 535,269
Estimated fair value	447,445	489,181
Commercial Mortgage Backed Securities Issued by US Government Agencies [Member]
Investment securities not due at a single maturity date, amortized cost	133,806
Investment securities not due at a single maturity date, estimated fair value	123,078
Amortized Cost	133,806	129,321
Estimated fair value	123,078	115,952
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Investment securities not due at a single maturity date, amortized cost	244,574
Investment securities not due at a single maturity date, estimated fair value	229,633
Amortized Cost	244,574	256,694
Estimated fair value	$ 229,633	$ 235,931