Note 6 - Employee Benefit Plans - Benefit Obligation, Fair Value of Plan Assets, Funded Status and Liability of Swiss Plan (Details) - Swiss Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Benefit obligation at beginning of year	$ (32,241)	$ (29,910)
Service cost	(1,310)	(920)	$ (925)
Interest cost	(67)	(267)	(207)
Actuarial gain	1,916	(1,456)
Participant contributions	(1,136)	(1,434)
Benefits paid	419	2,313
Plan change	944	0
Settlements	3,446	0
Foreign currency exchange adjustment	(3,010)	(567)
Benefit obligation at end of year	(31,039)	(32,241)	(29,910)
Fair value of plan assets at beginning of year	18,705	18,088
Return on assets, net of actuarial loss	129	281
Employer contributions	886	882
Participant contributions	1,136	1,434
Benefits paid	(419)	(2,313)
Settlements	(3,446)	0
Foreign currency exchange adjustment	1,765	333
Fair value of plan assets at end of year	18,756	18,705	$ 18,088
Net liability at end of year	$ (12,283)	$ (13,536)