Note 7 - Benefit Plans - Benefit Plan Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Components of net periodic benefit cost:
Service cost	$ 533	$ 408
Interest cost	501	360
Expected return on plan assets	(540)	(476)
Amortization, net	74	84
Net periodic benefit cost	$ 568	$ 376