Note 8 - Retirement Plans - Components of Net Periodic Benefit Cost for Pension Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of net periodic pension cost:
Service cost		$ 3,130	$ 5,162
Interest cost	4,398	4,159	4,106
Expected return on plan assets	(4,836)	(4,782)	(4,200)
Recognized net actuarial loss	406	1,580	969
Net periodic pension (benefit) cost	$ (32)	$ 4,087	$ 6,037