Note 7 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Due in one year or less, Amortized Cost	$ 69,741
Due in one year or less, Fair Value	69,890
Due after one year through five years, Amortized Cost	479,550
Due after one year through five years, Fair Value	478,222
Due after five years through ten years, Amortized Cost	23,551
Due after five years through ten years, Fair Value	23,637
Due after ten years, Amortized Cost	895,610
Due after ten years, Fair Value	899,835
Total, Amortized Cost	1,468,452	$ 1,267,731
Total, Fair Value	$ 1,471,584	$ 1,242,509