Note 3 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Due in one year or less, Amortized Cost	$ 168,831
Due in one year or less, Fair Value	168,894
Due after one year through five years, Amortized Cost	304,348
Due after one year through five years, Fair Value	304,337
Due after five years through ten years, Amortized Cost	50,587
Due after five years through ten years, Fair Value	50,593
Due after ten years, Amortized Cost	919,964
Due after ten years, Fair Value	928,018
Total, Amortized Cost	1,443,730	$ 1,267,731
Total, Fair Value	$ 1,451,842	$ 1,242,509