Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Net sales	$ 144,084	$ 150,011	$ 283,005	$ 297,820
Semiconductor Test and Inspection [Member]
Net sales	131,428	137,578	259,441	274,272
PCB Test [Member]
Net sales	12,656	12,433	23,564	23,548
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	74,011	76,155	144,550	156,095
Systems [Member] | PCB Test [Member]
Net sales	8,109	8,407	14,949	15,379
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	57,417	61,424	114,891	118,177
Non-systems [Member] | PCB Test [Member]
Net sales	4,547	4,025	8,615	8,169
CHINA
Net sales	31,133	32,738	61,944	56,289
UNITED STATES
Net sales	20,550	19,408	39,628	36,509
Malaysia [Member]
Net sales	11,842	16,993	27,016	34,707
TAIWAN, PROVINCE OF CHINA
Net sales	22,490	17,202	36,371	32,172
PHILIPPINES
Net sales	13,288	11,395	23,310	25,936
Rest of the World [Member]
Net sales	$ 44,781	$ 52,275	$ 94,736	$ 112,207