Note 8 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018
Net sales	[1]	$ 143,498	$ 86,164	$ 441,318	$ 281,131
Profit (loss) for reportable segments		(2,317)	9,941	(30,002)	41,073
Interest expense		(5,000)	(11)	(15,789)	(33)
Interest income		190	337	603	913
Income (loss) from continuing operations before taxes		(9,203)	7,105	(52,553)	31,470
Total assets for reportable segments		1,071,609		1,071,609		$ 1,134,002	[2]
Total assets		3,863		3,863		3,820
Corporate, Non-Segment [Member]
Corporate expenses		(2,076)	(3,162)	(7,365)	(10,483)
Total assets for reportable segments		15,759		15,759		34,367
Semiconductor Test and Inspection [Member]
Net sales		132,820	86,164	407,092	281,131
Profit (loss) for reportable segments		(2,929)	9,941	(32,373)	41,073
Total assets for reportable segments		994,248		994,248		1,038,053
PCB Test [Member]
Net sales		10,678		34,226
Profit (loss) for reportable segments		612		2,371
Total assets for reportable segments		57,739		57,739		57,762
Semiconductor Test and Inspection and PCB Test [Member]
Total assets for reportable segments		$ 1,051,987		$ 1,051,987		$ 1,095,815

[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.

[2] Derived from December 29, 2018 audited financial statements