Note 6 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Due in one year or less, Amortized Cost		$ 520,258
Due in one year or less, Fair Value		520,058
Due after one year through five years, Amortized Cost		526,194
Due after one year through five years, Fair Value		521,010
Due after five years through ten years, Amortized Cost		95
Due after five years through ten years, Fair Value		102
Due after ten years (1), Amortized Cost	[1]	320,077
Due after ten years (1), Fair Value	[1]	327,181
Total, Amortized Cost		1,366,624	$ 1,317,012
Total, Fair Value		$ 1,368,351	$ 1,314,345	[2]

[1] Equity securities are reported in this category

[2] Preferred stock of government sponsored entities and other equity securities as of December 31, 2015 were reclassified as level 1 rather than level 2 as originally classified due to the availability of quoted prices in active markets.