Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Net sales	[1]	$ 143,498	$ 86,164	$ 441,318	$ 281,131
Semiconductor Test and Inspection [Member]
Net sales		132,820	86,164	407,092	281,131
PCB Test [Member]
Net sales		10,678		34,226
Systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	[1]	70,654	42,278	226,749	152,846
Systems [Member] | PCB Test [Member]
Net sales	[1]	6,853		22,232
Non-systems [Member] | Semiconductor Test and Inspection [Member]
Net sales	[1]	62,166	43,886	180,343	128,285
Non-systems [Member] | PCB Test [Member]
Net sales	[1]	3,825		11,994
CHINA
Net sales		31,076	23,628	87,365	63,011
UNITED STATES
Net sales		21,918	11,585	58,427	41,725
TAIWAN, PROVINCE OF CHINA
Net sales		20,341	5,916	52,513	11,762
Malaysia [Member]
Net sales		12,991	13,682	47,698	38,539
PHILIPPINES
Net sales		12,330	11,158	38,266	31,620
Rest of the World [Member]
Net sales		$ 44,842	$ 20,195	$ 157,049	$ 94,474

[1] After the acquisition of Xcerra on October 1, 2018 we report in two segments, Semiconductor Test & Inspection and PCB Test. Cohu's historical reported net sales would have been reported in our Semiconductor Test & Inspection segment and have been presented accordingly.