Note 14 - Selected Financial Information of Registrant Selected Financial Information of Registrant (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Total assets	$ 5,969,391	$ 5,642,100
Long-term debt	1,286,466	1,219,454
Total liabilities	3,308,993	3,145,169
Total stockholders' equity	2,660,398	2,496,931
Total liabilities and stockholders' equity	5,969,391	5,642,100
Parent Company
Condensed Financial Statements, Captions [Line Items]
Investments in subsidiaries, at equity in net assets	3,120,807	3,001,846
Total assets	4,210,871	3,992,716
Long-term debt	1,286,466	1,219,454
Total liabilities	1,550,473	1,495,785
Total stockholders' equity	2,660,398	2,496,931
Total liabilities and stockholders' equity	$ 4,210,871	$ 3,992,716