Note 6 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Service cost	$ 5,820	$ 5,334	$ 4,401
Interest cost	4,990	5,618	6,482
Expected return on plan assets	(9,252)	(7,489)	(5,982)
Amortization of prior service benefit	394	117	61
Amortization of net gain from earlier periods	4,502	4,652	4,389
Net periodic pension cost	$ 6,454	$ 8,232	$ 9,351