Note 10 - Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax provision at Federal statutory rate, amount									$ 73,368	$ 70,914	$ 104,407
Tax provision at Federal statutory rate, percent									21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit, amount									$ 33,276	$ 29,750	$ 20,616
State income taxes, net of Federal income tax benefit, percent									9.50%	8.80%	6.90%
Deferred taxes write-down due to Tax Cuts and Jobs Act, amount									$ 0	$ 0	$ 23,365
Deferred taxes write-down due to Tax Cuts and Jobs Act, percentage									0.00%	0.00%	7.80%
Excess deduction for stock option and RSUs, amount									$ (398)	$ (555)	$ (3,146)
Excess deduction for stock option and RSUs									(0.10%)	(0.20%)	(1.00%)
Non-taxable bargain purchase gain, amount									$ 0	$ (71)	$ (1,970)
Non-taxable bargain purchase gain									0.00%	0.00%	(0.70%)
Low income housing and other tax credits, amount									$ (37,519)	$ (34,517)	$ (20,656)
Low income housing and other tax credits									(10.70%)	(10.20%)	(6.90%)
Other, net, amount									$ 1,507	$ 281	$ (351)
Other, net									0.40%	0.10%	(0.10%)
Total income tax expense, amount	$ 16,290	$ 20,973	$ 14,383	$ 18,588	$ 17,193	$ 18,698	$ 11,046	$ 18,866	$ 70,234	$ 65,802	$ 122,265
Total income tax expense									20.10%	19.50%	41.00%