Note 8 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018	Dec. 29, 2018
Net sales	[1]	$ 150,011	$ 99,817	$ 297,820	$ 194,967
Segment profit (loss) before tax:
Profit (loss) for reportable segments		(13,660)	18,997	(27,685)	31,132
Interest expense		(5,282)	(11)	(10,789)	(22)
Interest income		191	329	413	576
Income (loss) from continuing operations before taxes		(20,299)	14,116	(43,350)	24,365
Total assets for reportable segments		1,103,504		1,103,504		$ 1,134,002	[2]
Total assets		4,165		4,165		3,820
Corporate, Non-Segment [Member]
Segment profit (loss) before tax:
Corporate expenses		(1,548)	(5,199)	(5,289)	(7,321)
Total assets for reportable segments		15,960		15,960		34,367
Semiconductor Test and Inspection [Member]
Net sales		137,578	99,817	274,272	194,967
Segment profit (loss) before tax:
Profit (loss) for reportable segments		(14,400)	18,997	(29,444)	31,132
Total assets for reportable segments		1,021,348		1,021,348		1,038,053
PCB Test [Member]
Net sales		12,433		23,548
Segment profit (loss) before tax:
Profit (loss) for reportable segments		740		1,759
Total assets for reportable segments		62,031		62,031		57,762
Semiconductor Test and Inspection and PCB Test [Member]
Segment profit (loss) before tax:
Total assets for reportable segments		$ 1,083,379		$ 1,083,379		$ 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