Note 6 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Due in one year or less, Amortized Cost		$ 289,859
Due in one year or less, Fair Value		289,923
Due after one year through five years, Amortized Cost		353,931
Due after one year through five years, Fair Value		353,682
Due after five years through ten years, Amortized Cost		75,117
Due after five years through ten years, Fair Value		75,076
Due after ten years (1), Amortized Cost	[1]	564,901
Due after ten years (1), Fair Value	[1]	579,788
Total, Amortized Cost		1,283,808	$ 1,595,723
Total, Fair Value		$ 1,298,469	$ 1,586,352

[1] Equity securities are reported in this category