Note 7 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Due in one year or less, Amortized Cost		$ 415,782
Due in one year or less, Fair Value		415,555
Due after one year through five years, Amortized Cost		465,328
Due after one year through five years, Fair Value		459,924
Due after five years through ten years, Amortized Cost		8,658
Due after five years through ten years, Fair Value		8,647
Due after ten years (1), Amortized Cost	[1]	475,187
Due after ten years (1), Fair Value	[1]	484,361
Total, Amortized Cost		1,364,955	$ 1,317,012
Total, Fair Value		$ 1,368,487	$ 1,314,345

[1] Equity securities are reported in this category