Note 6 - Investments by Contractual Maturity Date (Details) - USD ($) $ in Thousands		Jun. 30, 2016	Dec. 31, 2015
Due in one year or less, Amortized Cost		$ 169,984
Due in one year or less, Fair Value		170,062
Due after one year through five years, Amortized Cost		254,283
Due after one year through five years, Fair Value		253,727
Due after five years through ten years, Amortized Cost		20,324
Due after five years through ten years, Fair Value		19,639
Due after ten years (1), Amortized Cost	[1]	782,578
Due after ten years (1), Fair Value	[1]	798,476
Securities available-for-sale, amortized cost		1,227,169	$ 1,595,723
Securities available-for-sale (amortized cost of $1,227,169 in 2016 and $1,595,723 in 2015		$ 1,241,904	$ 1,586,352

[1] Equity securities are reported in this category