Note 9 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 29, 2018		Sep. 29, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 30, 2017		Sep. 30, 2017		Jul. 01, 2017		Apr. 01, 2017		Dec. 29, 2018		Dec. 30, 2017	Dec. 31, 2016
Net sales by segment:
Net sales	$ 170,637	[1],[2]	$ 86,164	[1],[2]	$ 99,817	[1],[2]	$ 95,150	[1],[2]	$ 84,090	[1],[2]	$ 93,651	[1]	$ 93,866	[1]	$ 81,097	[1]	$ 451,768	[1],[2]	$ 352,704	$ 282,084
Segment profit (loss) before tax:
Profit (loss) for reportable segments																	(2,665)		42,535	13,516
Interest expense																	(4,977)		(54)
Interest income																	1,187		671	342
Income (loss) from continuing operations before taxes																	(31,912)		35,365	6,007
Depreciation and amortization by segment deducted in arriving at profit (loss):
Depreciation																	8,850		4,987	3,509
Amortization of Intangible Assets, Total	11,600		$ 600		$ 700		$ 700		700		$ 700		$ 600		$ 700		17,197		4,208	6,903
Total depreciation and amortization for reportable segments																	26,047		9,195	10,412
Capital expenditures																	4,967		6,093	3,452
Total assets by segment:
Total assets for reportable segments	1,134,002								420,457								1,134,002		420,457	345,512
Discontinued operations	3,820																3,820
Corporate, Non-Segment [Member]
Segment profit (loss) before tax:
Corporate expenses																	(25,457)		(7,787)	(7,851)
Total assets by segment:
Total assets for reportable segments	34,367								52,299								34,367		52,299	54,004
Semiconductor Test and Inspection [Member]
Net sales by segment:
Net sales																	443,276		352,704	282,084
Segment profit (loss) before tax:
Profit (loss) for reportable segments																	2,489		42,535	13,516
Depreciation and amortization by segment deducted in arriving at profit (loss):
Depreciation																	8,636		4,987	3,509
Capital expenditures																	4,957		6,093	3,452
Total assets by segment:
Total assets for reportable segments	1,038,053								368,158								1,038,053		368,158	291,508
PCB Test [Member]
Net sales by segment:
Net sales																	8,492
Segment profit (loss) before tax:
Profit (loss) for reportable segments																	(5,154)
Depreciation and amortization by segment deducted in arriving at profit (loss):
Depreciation																	214
Capital expenditures																	10
Total assets by segment:
Total assets for reportable segments	57,762																57,762
Semiconductor Test and Inspection and PCB Test [Member]
Total assets by segment:
Total assets for reportable segments	$ 1,095,815								$ 368,158								$ 1,095,815		$ 368,158	$ 291,508

[1] All quarters presented above were comprised of 13 weeks, except for the first quarter ended March 25, 2017, and the third quarter ended September 30, 2017, which were comprised of 12 and 14 weeks, respectively.

[2] 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 the fourth quarter of 2018 include charges related to the acquisition of Xcerra as follows - $37.8 million in restructuring charges comprised of $19.1 million of inventory end-of-manufacturing write-downs related to one of Xcerra's products, employee severance costs of $17.8 million and $0.9 million for other restructuring costs. We also recorded $13.1 million for the amortization of acquisition-related intangibles.