Note 12 - Income Taxes (Details) - Income Tax Reconciliation (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Reconciliation [Abstract]
Tax provision at Federal statutory rate									$ 76,928	$ 67,752	$ 64,248
Tax provision at Federal statutory rate									35.00%	35.00%	35.00%
State income taxes, net of Federal income tax benefit									14,324	12,573	11,772
State income taxes, net of Federal income tax benefit									6.60%	6.50%	6.40%
Interest on obligations of state and political subdivisions, which are exempt from Federal taxation										(348)	(1,456)
Interest on obligations of state and political subdivisions, which are exempt from Federal taxation										(0.20%)	(0.80%)
Low income housing and other tax credits									(10,014)	(10,056)	(9,353)
Low income housing and other tax credits									(4.60%)	(5.20%)	(5.10%)
Other, net									727	514	917
Other, net									0.30%	0.30%	0.50%
Total income tax expense	$ 21,021	$ 22,313	$ 20,741	$ 17,890	$ 17,946	$ 19,029	$ 16,573	$ 16,887	$ 81,965	$ 70,435	$ 66,128
Total income tax expense									37.30%	36.40%	36.00%