Note 7 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Due in one year or less, Amortized Cost	$ 85,713
Due in one year or less, Fair Value	85,764
Due after one year through five years, Amortized Cost	35,967
Due after one year through five years, Fair Value	35,481
Due after five years through ten years, Amortized Cost	175,943
Due after five years through ten years, Fair Value	180,203
Due after ten years, Amortized Cost	600,840
Due after ten years, Fair Value	607,396
Total, Amortized Cost	898,463	$ 1,019,230
Total, Fair Value	$ 908,844	$ 1,036,550