Note 6 - Employee Benefit Plans - Net Periodic Benefit Cost of Swiss Plan (Details) - Swiss Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Service cost	$ 1,310	$ 920	$ 925
Interest cost	67	267	207
Expected return on assets	(200)	(168)	(124)
Settlements	292	0	0
Net periodic costs	$ 1,469	$ 1,019	$ 1,008