Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 26, 2020	[1]	Sep. 26, 2020	[1]	Jun. 27, 2020	[1]	Mar. 28, 2020	[1]	Dec. 28, 2019	[1]	Sep. 28, 2019	[1]	Jun. 29, 2019	[1]	Mar. 30, 2019	[1]	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Net sales	$ 202,355		$ 150,647		$ 144,084		$ 138,921		$ 142,011		$ 143,498		$ 150,011		$ 147,809		$ 636,007	$ 583,329	$ 451,768
Semiconductor Test and Inspection [Member]
Net sales																	585,240	540,878	443,276
PCB Test [Member]
Net sales																	50,767	42,451	8,492
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales																	317,821	299,473	249,514
Systems [Member] | PCB Test [Member]
Net sales																	33,293	25,928	6,565
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales																	267,419	241,405	193,737
Non-systems [Member] | PCB Test [Member]
Net sales																	$ 17,474	$ 16,523	$ 1,952

[1] All quarters presented above were comprised of 13 weeks.