Note 8 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019	Dec. 28, 2019
Net sales	$ 150,647	$ 143,498	$ 433,652	$ 441,318
Segment profit (loss) before tax:
Profit (loss) for reportable segments	(2,384)	(2,317)	(13,283)	(30,002)
Interest expense	(3,021)	(5,000)	(10,904)	(15,789)
Interest income	42	190	210	603
Gain on extinguishment of debt	293	0	293	0
Loss from continuing operations before taxes	(5,530)	(9,203)	(28,443)	(52,553)
Assets, Total	1,046,353		1,046,353		$ 1,077,710	[1]
Discontinued operations	0		0		3,618
Corporate, Non-Segment [Member]
Segment profit (loss) before tax:
Corporate expenses	(460)	(2,076)	(4,759)	(7,365)
Assets, Total	43,638		43,638		18,398
Semiconductor Test and Inspection [Member]
Net sales	137,225	132,820	396,666	407,092
Segment profit (loss) before tax:
Profit (loss) for reportable segments	(4,093)	(2,929)	(17,997)	(32,373)
Assets, Total	941,086		941,086		998,756
PCB Test [Member]
Net sales	13,422	10,678	36,986	34,226
Segment profit (loss) before tax:
Profit (loss) for reportable segments	1,709	$ 612	4,714	$ 2,371
Assets, Total	61,629		61,629		56,938
Semiconductor Test and Inspection and PCB Test [Member]
Segment profit (loss) before tax:
Assets, Total	$ 1,002,715		$ 1,002,715		$ 1,055,694

[1] Derived from December 28, 2019 audited financial statements