Note 7 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Due in one year or less, Amortized Cost	$ 182,047
Due in one year or less, Fair Value	182,289
Due after one year through five years, Amortized Cost	44,028
Due after one year through five years, Fair Value	44,044
Due after five years through ten years, Amortized Cost	176,079
Due after five years through ten years, Fair Value	178,429
Due after ten years, Amortized Cost	658,821
Due after ten years, Fair Value	675,778
Total, Amortized Cost	1,060,975	$ 1,443,730
Total, Fair Value	$ 1,080,540	$ 1,451,842