Note 11 - Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Tax provision at Federal statutory rate, amount									$ 84,770	$ 77,384	$ 76,928
Tax provision at Federal statutory rate, percent									35.00%	35.00%	35.00%
State income taxes, net of Federal income tax benefit, amount									$ 17,250	$ 14,656	$ 14,324
State income taxes, net of Federal income tax benefit, percent									7.10%	6.60%	6.60%
Low income housing and other tax credits, amount									$ (37,901)	$ (30,986)	$ (10,014)
Low income housing and other tax credits, percent									(15.60%)	(14.00%)	(4.60%)
Non-deductible stock options expense, amount									$ 3,469
Non-deductible stock options expense, percent									1.40%
Other, net, amount									$ (487)	$ (1,067)	$ 727
Other, net, percent									(0.20%)	(0.50%)	0.30%
Total income tax expense	$ 16,345	$ 15,808	$ 12,273	$ 22,675	$ 16,787	$ 12,098	$ 9,738	$ 21,364	$ 67,101	$ 59,987	$ 81,965
Total income tax expense, percent									27.70%	27.10%	37.30%