Note 6 - Retirement Plans - Components of Net Periodic Benefit Cost for Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest cost	$ 1,106	$ 807
Expected return on plan assets	(1,536)	(976)
Loss amortization	169	84
Net periodic benefit cost	$ (261)	$ (85)