Note 8 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019	Dec. 28, 2019
Net sales by segment:
Net sales	$ 138,921	$ 147,809
Segment profit (loss) before tax:
Profit (loss) for reportable segments	(10,579)	(14,025)
Interest expense	(4,427)	(5,507)
Interest income	147	222
Loss from continuing operations before taxes	(18,310)	(23,051)
Total assets for reportable segments	1,072,155		$ 1,077,710	[1]
Discontinued operations			3,618
Corporate, Non-Segment [Member]
Segment profit (loss) before tax:
Corporate expenses	(3,451)	(3,741)
Total assets for reportable segments	46,710		18,398
Semiconductor Test and Inspection [Member]
Net sales by segment:
Net sales	128,013	136,694
Segment profit (loss) before tax:
Profit (loss) for reportable segments	(11,573)	(15,044)
Total assets for reportable segments	966,562		998,756
PCB Test [Member]
Net sales by segment:
Net sales	10,908	11,115
Segment profit (loss) before tax:
Profit (loss) for reportable segments	994	$ 1,019
Total assets for reportable segments	58,883		56,938
Semiconductor Test and Inspection and PCB Test [Member]
Segment profit (loss) before tax:
Total assets for reportable segments	$ 1,025,445		$ 1,055,694

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