Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 25, 2021	Sep. 26, 2020	Sep. 25, 2021	Sep. 26, 2020
Net sales	$ 225,063	$ 150,647	$ 695,354	$ 433,652
Semiconductor Test and Inspection [Member]
Net sales	225,063	137,225	668,594	396,666
PCB Test [Member]
Net sales	0	13,422	26,760	36,986
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	146,010	70,360	433,830	214,910
Systems [Member] | PCB Test [Member]
Net sales	0	8,990	17,831	23,939
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	79,053	66,865	234,764	181,756
Non-systems [Member] | PCB Test [Member]
Net sales	0	4,432	8,929	13,047
CHINA
Net sales	60,205	30,423	171,653	92,367
PHILIPPINES
Net sales	49,382	11,860	119,669	35,170
TAIWAN, PROVINCE OF CHINA
Net sales	15,006	22,689	74,392	59,060
Malaysia [Member]
Net sales	21,086	11,435	63,481	38,451
UNITED STATES
Net sales	15,498	32,111	57,435	71,739
Rest of the World [Member]
Net sales	$ 63,886	$ 42,129	$ 208,724	$ 136,865