Note 11 - Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2015
Tax provision at Federal statutory rate, amount									$ 104,407	$ 84,770		$ 77,384
Tax provision at Federal statutory rate, percent									35.00%	35.00%		35.00%
State income taxes, net of Federal income tax benefit, amount									$ 20,616	$ 17,250		$ 14,656
State income taxes, net of Federal income tax benefit, percent									6.90%	7.10%		6.60%
Deferred taxes write-down due to Tax Cuts and Jobs Act, amount									$ 23,365
Deferred taxes write-down due to Tax Cuts and Jobs Act, percentage									7.80%
Excess deduction for stock option and RSUs, amount									$ (3,146)
Excess deduction for stock option and RSUs, percentage									(1.00%)
Non-taxable bargain purchase gain, amount									$ (1,970)
Non-taxable bargain purchase gain, percentage									(0.70%)
Low income housing and other tax credits, amount									$ (20,656)	$ (37,901)		$ (30,986)
Low income housing and other tax credits, percent									(6.90%)	(15.60%)		(14.00%)
Non-deductible stock options expense, amount										$ 3,469
Non-deductible stock options expense, percent										1.40%
Other, net, amount									$ (351)	$ (487)		$ (1,067)
Other, net, percent									(0.10%)	(0.20%)		(0.50%)
Total income tax expense	$ 51,166	$ 35,163	$ 15,431	$ 20,505	$ 16,345	$ 15,808	$ 12,273	$ 22,675	$ 122,265	$ 67,101	$ 59,987	$ 59,987
Total income tax expense, percent									41.00%	27.70%		27.10%