Note 6 - Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income tax at federal statutory rate	$ 196,326	$ 269,088	$ 209,952
State tax, net of federal effect	28,997	41,624	37,223
Benefit of stock compensation	(7,442)	(7,584)	(7,583)
199/R&D credit	(622)	5,839	(1,524)
Federal 1341 Claim	14,616	(0)	(0)
Nondeductible meals and entertainment	2,331	294	130
Change in effective state tax rate, net of federal benefit	(193)	1,561	(724)
Other, net	1,819	1,200	1,492
Total tax expense/(benefit)	$ 206,600	$ 312,022	$ 238,966