Note 7 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Service cost	$ 1,334	$ 1,100
Interest cost	1,404	1,620
Expected return on plan assets	(1,872)	(1,496)
Amortization of prior service cost	29	15
Amortization of net loss	1,163	1,097
Net periodic pension cost	$ 2,058	$ 2,336