Note 7 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Due in one year or less, Amortized Cost	$ 181,868
Due in one year or less, Fair Value	182,062
Due after one year through five years, Amortized Cost	54,118
Due after one year through five years, Fair Value	54,320
Due after five years through ten years, Amortized Cost	155,525
Due after five years through ten years, Fair Value	157,920
Due after ten years, Amortized Cost	731,483
Due after ten years, Fair Value	751,800
Total, Amortized Cost	1,122,994	$ 1,443,730
Total, Fair Value	$ 1,146,102	$ 1,451,842