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. 25, 2021	Dec. 26, 2020	Dec. 28, 2019
Benefit obligation at beginning of year	$ (31,039)	$ (32,241)
Service cost	(1,223)	(1,310)	$ (920)
Interest cost	(61)	(67)	(267)
Actuarial gain	1,179	1,916
Participant contributions	(1,780)	(1,136)
Benefits paid	436	419
Plan change	1,076	944
Settlements	1,653	3,446
Foreign currency exchange adjustment	994	(3,010)
Benefit obligation at end of year	(28,765)	(31,039)	(32,241)
Fair value of plan assets at beginning of year	18,756	18,705
Return on assets, net of actuarial loss	207	129
Employer contributions	878	886
Participant contributions	1,780	1,136
Benefits paid	(436)	(419)
Settlements	(1,653)	(3,446)
Foreign currency exchange adjustment	(613)	1,765
Fair value of plan assets at end of year	18,919	18,756	$ 18,705
Net liability at end of year	$ (9,846)	$ (12,283)