Note 3 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Due in one year or less, Amortized Cost	$ 131,974
Due in one year or less, Fair Value	132,026
Due after one year through five years, Amortized Cost	54,820
Due after one year through five years, Fair Value	54,688
Due after five years through ten years, Amortized Cost	190,440
Due after five years through ten years, Fair Value	194,029
Due after ten years, Amortized Cost	641,996
Due after ten years, Fair Value	655,807
Total, Amortized Cost	1,019,230	$ 1,443,730
Total, Fair Value	$ 1,036,550	$ 1,451,842