Note 6 - Employee Benefit Plans - Change in Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Benefit obligation at beginning of year	$ 192,954	$ 172,909
Service cost	5,820	5,334	$ 4,401
Interest cost	4,990	5,618	6,482
Amendments	550	0
Change due to mortality change	548	(1,521)
Change due to discount rate change	(5,865)	17,040
Actuarial return (loss)	4,342	121
Benefits paid	(7,477)	(6,547)
Benefit obligation at end of year	195,862	192,954	172,909
Fair value of plan assets at beginning of year	148,052	116,067
Actual return on plan assets	27,049	14,801
Employer contributions	22,250	23,731
Benefits paid	(7,477)	(6,547)
Fair value of plan assets at end of year	189,874	148,052	$ 116,067
Underfunded status at end of year	$ (5,988)	$ (44,902)