Note 10 - Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Tax provision at Federal statutory rate, amount									$ 53,333	$ 73,368	$ 70,914
Tax provision at Federal statutory rate, percent									21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit, amount									$ 23,602	$ 33,276	$ 29,750
State income taxes, net of Federal income tax benefit, percent									9.30%	9.50%	8.80%
Excess deduction for stock option and RSUs, amount									$ 264	$ (398)	$ (555)
Excess deduction for stock option and RSUs, percent									0.10%	(0.10%)	(0.20%)
Non-taxable bargain purchase gain, amount									$ 0	$ 0	$ (71)
Non-taxable bargain purchase gain, percent									0.00%	0.00%	0.00%
Low income housing and other tax credits, amount									$ (52,979)	$ (37,519)	$ (34,517)
Low income housing and other tax credits, percent									(20.80%)	(10.70%)	(10.20%)
Other, net, amount									$ 885	$ 1,507	$ 281
Other, net, percent									0.30%	0.40%	0.10%
Total income tax expense	$ 10,332	$ 2,190	$ 3,492	$ 9,091	$ 16,290	$ 20,973	$ 14,383	$ 18,588	$ 25,105	$ 70,234	$ 65,802
Total income tax expense, percent									9.90%	20.10%	19.50%