Note 9 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 28, 2019		Sep. 28, 2019	[1]	Jun. 29, 2019	[1]	Mar. 30, 2019	[1]	Dec. 29, 2018		Sep. 29, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Net sales by segment:
Net sales	$ 142,011	[1]	$ 143,498		$ 150,011		$ 147,809		$ 170,637	[1]	$ 86,164		$ 99,817		$ 95,150		$ 583,329	$ 451,768	$ 352,704
Segment profit (loss) before tax:
Profit (loss) for reportable segments																	(42,437)	(2,665)	42,535
Interest expense																	(20,556)	(4,977)	(54)
Interest income																	764	1,187	671
Income (loss) from continuing operations before taxes																	(72,077)	(31,912)	35,365
Depreciation																	19,300	8,800	5,000
Total depreciation and amortization for reportable segments																	58,871	26,047	9,195
Capital expenditures																	18,000	4,967	6,093
Total assets by segment:
Total assets for reportable segments	1,077,710								1,134,002								1,077,710	1,134,002	420,457
Discontinued operations	3,618								3,820								3,618	3,820
Corporate, Non-Segment [Member]
Segment profit (loss) before tax:
Corporate expenses																	(9,848)	(25,457)	(7,787)
Total assets by segment:
Total assets for reportable segments	18,398								34,367								18,398	34,367	52,299
Semiconductor Test and Inspection [Member]
Net sales by segment:
Net sales																	540,878	443,276	352,704
Segment profit (loss) before tax:
Profit (loss) for reportable segments																	(45,072)	2,489	42,535
Depreciation																	56,621	24,634	9,195
Capital expenditures																	17,831	4,957	6,093
Total assets by segment:
Total assets for reportable segments	998,756								1,038,053								998,756	1,038,053	368,158
PCB Test [Member]
Net sales by segment:
Net sales																	42,451	8,492
Segment profit (loss) before tax:
Profit (loss) for reportable segments																	2,635	(5,154)
Depreciation																	2,250	1,413
Capital expenditures																	169	10
Total assets by segment:
Total assets for reportable segments	56,938								57,762								56,938	57,762
Semiconductor Test and Inspection and PCB Test [Member]
Total assets by segment:
Total assets for reportable segments	$ 1,055,694								$ 1,095,815								$ 1,055,694	$ 1,095,815	$ 368,158

[1] All quarters presented above were comprised of 13 weeks. We acquired Xcerra on October 1, 2018. The results of Xcerra have been included in our results of operations from the date of acquisition. See Note 2, “Business Acquisitions” for additional information regarding this transaction. Total operating expenses in 2019 and 2018 include acquisition costs and amounts related to the integration and our announced restructuring plan as follows. The fourth quarter of 2018 includes $19.1 million of inventory write-offs, $14.8 million of amortization of inventory step-up, and $18.7 million of restructuring charges. The first quarter of 2019 includes $6.0 million of amortization of inventory step-up. The second quarter of 2019 includes $8.5 million of restructuring charges.