Note 7 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Due in one year or less, Amortized Cost	$ 82,224
Due in one year or less, Fair Value	81,977
Due after one year through five years, Amortized Cost	254,226
Due after one year through five years, Fair Value	252,788
Due after five years through ten years, Amortized Cost	86,506
Due after five years through ten years, Fair Value	87,304
Due after ten years, Amortized Cost	907,276
Due after ten years, Fair Value	933,104
Total, Amortized Cost	1,330,232	$ 1,443,730
Total, Fair Value	$ 1,355,173	$ 1,451,842