Note 6 - Investment Securities - Investments by Contractual Maturity Date (Details) - USD ($)		Mar. 31, 2017	Dec. 31, 2016		Mar. 31, 2016
Due in one year or less, Amortized Cost		$ 370,028,000
Due in one year or less, Fair Value		369,892,000
Due after one year through five years, Amortized Cost		527,354,000
Due after one year through five years, Fair Value		519,205,000
Due after five years through ten years, Amortized Cost		103,000
Due after five years through ten years, Fair Value		111,000
Due after ten years (1), Amortized Cost	[1]	333,300,000
Due after ten years (1), Fair Value	[1]	338,521,000
Total, Amortized Cost		1,230,785,000	$ 1,317,012,000
Total, Fair Value		$ 1,227,729,000	$ 1,314,345,000	[2]	$ 1,300,000,000

[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.