Note 7 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Due in one year or less, Amortized Cost	$ 19,993
Due in one year or less, Fair Value	20,103
Due after one year through five years, Amortized Cost	429,449
Due after one year through five years, Fair Value	427,578
Due after five years through ten years, Amortized Cost	41,718
Due after five years through ten years, Fair Value	41,710
Due after ten years, Amortized Cost	931,271
Due after ten years, Fair Value	938,047
Total, Amortized Cost	1,422,431	$ 1,267,731
Total, Fair Value	$ 1,427,438	$ 1,242,509