Note 5 - Employee Benefit Plans - Change in Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan [Abstract]
Benefit obligation at beginning of year	$ 195,862	$ 192,954
Service cost	6,262	5,820	$ 5,334
Interest cost	5,476	4,990	5,618
Amendments	0	550
Change due to mortality change	486	548
Change due to discount rate change	(54,977)	(5,865)
Actuarial return (loss)	1,841	4,342
Benefits paid	(6,807)	(7,477)
Benefit obligation at end of year	148,143	195,862	192,954
Fair value of plan assets at beginning of year	189,874	148,052
Actual return on plan assets	(18,238)	27,049
Employer contributions	10,330	22,250
Benefits paid	(6,807)	(7,477)
Fair value of plan assets at end of year	175,159	189,874	$ 148,052
Funded/(underfunded) status at end of year	$ 27,016	$ (5,988)