Note 7 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Service cost	$ 1,100	$ 1,252	$ 2,200	$ 2,504
Interest cost	1,620	1,377	3,240	2,754
Expected return on plan assets	(1,496)	(1,634)	(2,992)	(3,268)
Amortization of prior service cost	15	15	30	30
Amortization of net loss	1,097	931	2,194	1,862
Net periodic pension cost	$ 2,336	$ 1,941	$ 4,672	$ 3,882