Note 12 - Income Taxes (Details) - Income Tax Reconciliation - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Reconciliation [Abstract]
Tax provision at Federal statutory rate									$ 77,384	$ 76,928	$ 67,752
Tax provision at Federal statutory rate									35.00%	35.00%	35.00%
State income taxes, net of Federal income tax benefit									$ 14,656	$ 14,324	$ 12,573
State income taxes, net of Federal income tax benefit									6.60%	6.60%	6.50%
Interest on obligations of state and political subdivisions, which are exempt from Federal taxation											$ (348)
Interest on obligations of state and political subdivisions, which are exempt from Federal taxation											(0.20%)
Low income housing and other tax credits									$ (30,986)	$ (10,014)	$ (10,056)
Low income housing and other tax credits									(14.00%)	(4.60%)	(5.20%)
Other, net									$ (1,067)	$ 727	$ 514
Other, net									(0.50%)	0.30%	0.30%
Total income tax expense	$ 16,787	$ 12,098	$ 9,738	$ 21,364	$ 21,021	$ 22,313	$ 20,741	$ 17,890	$ 59,987	$ 81,965	$ 70,435
Total income tax expense									27.10%	37.30%	36.40%