Note 16 - Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 28, 2019		Sep. 28, 2019		Jun. 29, 2019		Mar. 30, 2019	[1]	Dec. 29, 2018		Sep. 29, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Net sales	$ 142,011	[1]	$ 143,498	[1]	$ 150,011	[1]	$ 147,809		$ 170,637	[1]	$ 86,164		$ 99,817		$ 95,150		$ 583,329	$ 451,768	$ 352,704
Cost of sales:	87,936	[1],[2]	84,565	[1],[2]	87,605	[1],[2]	93,394	[2]	128,718	[1],[2]	51,142	[2]	57,677	[2]	54,923	[2]	353,500	292,460
Income (loss) from continuing operations	(16,281)		(10,480)		(19,383)		(22,851)		(57,116)		4,803		11,648		8,122		(68,995)	(32,543)	33,121
Net income (loss)	(17,320)		(10,326)	[1]	(19,359)	[1]	(22,687)		(56,997)		4,803	[2]	11,648		8,122		(69,692)	(32,424)	32,843
Net income (loss) attributable to Cohu	$ (17,266)	[1]	$ (10,468)	[1]	$ (19,323)	[1]	$ (22,643)		$ (56,754)		$ 4,803		$ 11,648		$ 8,122		$ (69,700)	$ (32,181)	$ 32,843
Income (loss) from continuing operations (in dollars per share)	$ (0.39)	[1],[3]	$ (0.25)	[1],[3]	$ (0.47)	[1],[3]	$ (0.56)	[3]	$ (1.40)	[1],[3]	$ 0.17	[3]	$ 0.40	[3]	$ 0.28	[3]	$ (1.68)	$ (1.02)	$ 1.19
Net income (loss) (in dollars per share)	(0.42)	[1],[3]	(0.25)	[1],[3]	(0.47)	[1],[3]	(0.55)	[3]	(1.40)	[1],[3]	0.17	[3]	0.40	[3]	0.28	[3]	(1.69)	(1.01)	1.18
Income (loss) from continuing operations before non-controlling interest (in dollars per share)	(0.39)	[1],[3]	(0.25)	[1],[3]	(0.47)	[1],[3]	(0.56)	[3]	(1.40)	[1],[3]	0.16	[3]	0.39	[3]	0.28	[3]	(1.68)	(1.02)	1.15
Net income (loss) (in dollars per share)	$ (0.42)	[1],[3]	$ (0.25)	[1],[3]	$ (0.47)	[1],[3]	$ (0.55)	[3]	$ (1.40)	[1],[3]	$ 0.16	[3]	$ 0.39	[3]	$ 0.28	[3]	$ (1.69)	$ (1.01)	$ 1.14

[1] All quarters presented above were comprised of 13 weeks. We acquired Xcerra on October 1, 2018. The results of Xcerra have been included in our results of operations from the date of acquisition. See Note 2, “Business Acquisitions” for additional information regarding this transaction. Total operating expenses in 2019 and 2018 include acquisition costs and amounts related to the integration and our announced restructuring plan as follows. The fourth quarter of 2018 includes $19.1 million of inventory write-offs, $14.8 million of amortization of inventory step-up, and $18.7 million of restructuring charges. The first quarter of 2019 includes $6.0 million of amortization of inventory step-up. The second quarter of 2019 includes $8.5 million of restructuring charges.

[2] Cost of sales is shown exclusive of the amortization of purchased intangible assets.

[3] The sum of the four quarters may not agree to the year total due to rounding or losses within a quarter and the inclusion or exclusion of common stock equivalents.