Note 6 - Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income tax at federal statutory rate	$ 269,088	$ 209,952	$ 139,865
State tax, net of federal effect	41,624	37,223	20,071
Benefit of stock compensation	(7,584)	(7,583)	(3,503)
199/R&D credit	5,839	(1,524)	0
Nondeductible meals and entertainment	294	130	1,344
Change in effective state tax rate, net of federal benefit	1,561	(724)	98
Other, net	1,200	1,492	2,115
Total tax expense/(benefit)	$ 312,022	$ 238,966	$ 159,990