Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 29, 2018	[1],[2]	Sep. 29, 2018	[1],[2]	Jun. 30, 2018	[1],[2]	Mar. 31, 2018	[1],[2]	Dec. 30, 2017	[1],[2]	Sep. 30, 2017	[1]	Jul. 01, 2017	[1]	Apr. 01, 2017	[1]	Dec. 29, 2018		Dec. 30, 2017	Dec. 31, 2016
Net sales	$ 170,637		$ 86,164		$ 99,817		$ 95,150		$ 84,090		$ 93,651		$ 93,866		$ 81,097		$ 451,768	[1],[2]	$ 352,704	$ 282,084
Semiconductor Test and Inspection [Member]
Net sales																	443,276		352,704	282,084
Semiconductor Test and Inspection [Member] | Systems [Member]
Net sales																	249,514		197,454
Semiconductor Test and Inspection [Member] | Non-systems [Member]
Net sales																	193,737		155,250
PCB Test [Member]
Net sales																	8,492
PCB Test [Member] | Systems [Member]
Net sales																	6,565
PCB Test [Member] | Non-systems [Member]
Net sales																	$ 1,952

[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.