Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 27, 2021	Mar. 28, 2020
Net sales	$ 225,488	$ 138,921
Semiconductor Test and Inspection [Member]
Net sales	212,406	128,013
PCB Test [Member]
Net sales	13,082	10,908
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	138,159	70,539
Systems [Member] | PCB Test [Member]
Net sales	8,620	6,840
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	74,247	57,474
Non-systems [Member] | PCB Test [Member]
Net sales	4,462	4,068
CHINA
Net sales	54,265	30,811
PHILIPPINES
Net sales	33,754	10,022
TAIWAN, PROVINCE OF CHINA
Net sales	32,196	13,881
Malaysia [Member]
Net sales	23,259	15,174
UNITED STATES
Net sales	20,059	19,078
Rest of the World [Member]
Net sales	$ 61,955	$ 49,955