Note 9 - Retirement Plans - Components of Net Periodic Benefit Cost for Pension Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of net periodic pension cost:
Service cost	$ 0	$ 0
Interest cost	4,424	4,669	4,398
Expected return on plan assets	(6,145)	(5,648)	(4,836)
Recognized net actuarial loss	678	484	406
Net periodic pension benefit	$ (1,043)	$ (494)	$ (32)