Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Net sales	$ 150,647	$ 143,498	$ 433,652	$ 441,318
Semiconductor Test and Inspection [Member]
Net sales	137,225	132,820	396,666	407,092
PCB Test [Member]
Net sales	13,422	10,678	36,986	34,226
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	70,360	70,654	214,910	226,749
Systems [Member] | PCB Test [Member]
Net sales	8,990	6,853	23,939	22,232
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	66,865	62,166	181,756	180,343
Non-systems [Member] | PCB Test [Member]
Net sales	4,432	3,825	13,047	11,994
CHINA
Net sales	30,423	31,076	92,367	87,365
UNITED STATES
Net sales	32,111	21,918	71,739	58,427
Malaysia [Member]
Net sales	11,435	12,991	38,451	47,698
TAIWAN, PROVINCE OF CHINA
Net sales	22,689	20,341	59,060	52,513
PHILIPPINES
Net sales	11,860	12,330	35,170	38,266
Rest of the World [Member]
Net sales	$ 42,129	$ 44,842	$ 136,865	$ 157,049