Note 4 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Due in one year or less, Amortized Cost	$ 525,406
Due in one year or less, Fair Value	524,948
Due after one year through five years, Amortized Cost	227,132
Due after one year through five years, Fair Value	215,834
Due after five years through ten years, Amortized Cost	149,042
Due after five years through ten years, Fair Value	141,044
Due after ten years, Amortized Cost	824,500
Due after ten years, Fair Value	722,744
Total, Amortized Cost	1,726,080	$ 1,622,173
Total, Fair Value	$ 1,604,570	$ 1,473,348