Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 28, 2019	[1]	Sep. 28, 2019	[1]	Jun. 29, 2019	[1]	Mar. 30, 2019	[1]	Dec. 29, 2018	[1]	Sep. 29, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Net sales	$ 142,011		$ 143,498		$ 150,011		$ 147,809		$ 170,637		$ 86,164		$ 99,817		$ 95,150		$ 583,329	$ 451,768	$ 352,704
Semiconductor Test and Inspection [Member]
Net sales																	540,878	443,276	352,704
Semiconductor Test and Inspection [Member] | Systems [Member]
Net sales																	299,473	249,514	197,454
Semiconductor Test and Inspection [Member] | Non-systems [Member]
Net sales																	241,405	193,737	155,250
PCB Test [Member]
Net sales																	42,451	8,492
PCB Test [Member] | Systems [Member]
Net sales																	25,928	6,565
PCB Test [Member] | Non-systems [Member]
Net sales																	$ 16,523	$ 1,952

[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.