Note 7 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Due in one year or less, Amortized Cost	$ 149,234
Due in one year or less, Fair Value	149,243
Due after one year through five years, Amortized Cost	465,744
Due after one year through five years, Fair Value	459,017
Due after five years through ten years, Amortized Cost	5,820
Due after five years through ten years, Fair Value	5,662
Due after ten years, Amortized Cost	701,781
Due after ten years, Fair Value	695,931
Total, Amortized Cost	1,322,579	$ 1,267,731
Total, Fair Value	$ 1,309,853	$ 1,242,509