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. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Benefit obligation at beginning of year	$ (29,910)	$ (30,512)
Service cost	(920)	(925)	$ (907)
Interest cost	(267)	(207)	(198)
Actuarial gain (loss)	(1,456)	708
Participant contributions	(1,434)	(816)
Benefits paid	2,313	1,079
Plan change		199
Foreign currency exchange adjustment	(567)	564
Benefit obligation at end of year	(32,241)	(29,910)	(30,512)
Fair value of plan assets at beginning of year	18,088	17,746
Return on assets, net of actuarial loss	281	114
Employer contributions	882	816
Participant contributions	1,434	816
Benefits paid	(2,313)	(1,079)
Foreign currency exchange adjustment	333	(325)
Fair value of plan assets at end of year	18,705	18,088	$ 17,746
Net liability at end of year	$ (13,536)	$ (11,822)