Note 7 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Service cost	$ 1,100	$ 1,252	$ 3,300	$ 3,756
Interest cost	1,620	1,377	4,860	4,131
Expected return on plan assets	(1,496)	(1,634)	(4,488)	(4,902)
Amortization of prior service cost	15	15	45	45
Amortization of net loss	1,097	931	3,291	2,793
Net periodic pension cost	$ 2,336	$ 1,941	$ 7,008	$ 5,823