Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 26, 2021	Jun. 27, 2020	Jun. 26, 2021	Jun. 27, 2020
Net sales	$ 244,803	$ 144,084	$ 470,291	$ 283,005
Semiconductor Test and Inspection [Member]
Net sales	231,125	131,428	443,531	259,441
PCB Test [Member]
Net sales	13,678	12,656	26,760	23,564
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	149,661	74,011	287,820	144,550
Systems [Member] | PCB Test [Member]
Net sales	9,211	8,109	17,831	14,949
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	81,464	57,417	155,711	114,891
Non-systems [Member] | PCB Test [Member]
Net sales	4,467	4,547	8,929	8,615
CHINA
Net sales	57,183	31,133	111,448	61,944
PHILIPPINES
Net sales	36,533	13,288	70,287	23,310
TAIWAN, PROVINCE OF CHINA
Net sales	27,190	22,490	59,386	36,371
Malaysia [Member]
Net sales	19,136	11,842	42,395	27,016
UNITED STATES
Net sales	21,878	20,550	41,937	39,628
Rest of the World [Member]
Net sales	$ 82,883	$ 44,781	$ 144,838	$ 94,736