Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Net sales	$ 138,921	$ 147,809
Semiconductor Test and Inspection [Member]
Net sales	128,013	136,694
PCB Test [Member]
Net sales	10,908	11,115
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	70,539	79,940
Systems [Member] | PCB Test [Member]
Net sales	6,840	6,972
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	57,474	56,753
Non-systems [Member] | PCB Test [Member]
Net sales	4,068	4,144
CHINA
Net sales	30,811	23,551
UNITED STATES
Net sales	19,078	17,101
Malaysia [Member]
Net sales	15,174	17,714
TAIWAN, PROVINCE OF CHINA
Net sales	13,881	14,970
PHILIPPINES
Net sales	10,022	14,541
Rest of the World [Member]
Net sales	$ 49,955	$ 59,932