Note 10 - Income Taxes - Reconciliation of Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Federal income taxes due at statutory rate	$ 46,532	$ 34,774	$ 24,576
Interest on state and municipal securities and loans not taxable for federal income tax purposes	(1,188)	(1,484)	(2,070)
State franchise taxes, net of federal income tax benefit	18,117	14,315	9,757
Change in valuation reserve	0	0	1,776
Stock compensation deduction less than (in excess of) book expense	3	30	0
Tax credits	(2,943)	(3,439)	(2,621)
Dividend received deduction	(66)	(56)	(48)
Cash value life insurance	(597)	(421)	(389)
Other	(47)	(162)	(463)
Provision for income taxes	$ 59,811	$ 43,557	$ 30,518