Note 7 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Service cost	$ 1,334	$ 1,100	$ 2,668	$ 2,200
Interest cost	1,404	1,620	2,808	3,240
Expected return on plan assets	(1,872)	(1,496)	(3,744)	(2,992)
Amortization of prior service cost	29	15	58	30
Amortization of net loss	1,163	1,097	2,326	2,194
Net periodic pension cost	$ 2,058	$ 2,336	$ 4,116	$ 4,672