Note 15 - Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 29, 2018		Sep. 29, 2018		Jun. 30, 2018		Mar. 31, 2018	[1]	Dec. 30, 2017	[1],[2]	Sep. 30, 2017	[1]	Jul. 01, 2017	[1]	Apr. 01, 2017	[1]	Dec. 29, 2018		Dec. 30, 2017		Dec. 31, 2016
Net sales	$ 170,637	[1],[2]	$ 86,164	[1],[2]	$ 99,817	[1],[2]	$ 95,150	[2]	$ 84,090		$ 93,651		$ 93,866		$ 81,097		$ 451,768	[1],[2]	$ 352,704		$ 282,084
Cost of sales (c):	128,718	[1],[2],[3]	51,142	[1],[2],[3]	57,677	[1],[2],[3]	54,923	[2],[3]	48,993	[3]	56,065	[3]	56,166	[3]	48,073	[3]	292,460	[1],[2],[3],[4]	209,297	[3],[4]	182,086	[4]
Income (loss) from continuing operations	(57,116)	[1],[2]	4,803	[1]	11,648	[1]	8,122		6,895		8,755		10,708		6,763		(32,543)		33,121		3,260
Net income (loss)	(56,997)	[1],[2]	4,803	[1]	11,648	[1]	8,122		6,895		8,755		10,430		6,763		(32,424)		32,843		3,039
Net income (loss) attributable to Cohu	$ (56,754)	[1],[2]	$ 4,803	[1]	$ 11,648	[1]	$ 8,122		$ 6,895		$ 8,755		$ 10,430		$ 6,763		$ (32,181)		$ 32,843		$ 3,039
Income (loss) from continuing operations (in dollars per share)	$ (1.40)	[5]	$ 0.17	[5]	$ 0.40	[5]	$ 0.28	[5]	$ 0.24	[5]	$ 0.31	[5]	$ 0.39	[5]	$ 0.25	[5]	$ (1.02)	[5]	$ 1.19	[5]	$ 0.12
Net income (loss) (in dollars per share)	(1.40)	[1],[5]	0.17	[1],[5]	0.40	[1],[5]	0.28	[5]	0.24	[5]	0.31	[5]	0.38	[5]	0.25	[5]	(1.01)	[5]	1.18	[5]	0.11
Income (loss) from continuing operations before non-controlling interest (in dollars per share)	(1.40)	[1],[2],[5]	0.16	[1],[5]	0.39	[1],[5]	0.28	[5]	0.23	[5]	0.30	[5]	0.37	[5]	0.24	[5]	(1.02)	[5]	1.15	[5]	0.12
Net income (loss) attributable to Cohu (in dollars per share)	$ (1.40)	[1],[2],[5]	$ 0.16	[1],[5]	$ 0.39	[1],[5]	$ 0.28	[5]	$ 0.23	[5]	$ 0.30	[5]	$ 0.36	[5]	$ 0.24	[5]	$ (1.01)	[5]	$ 1.14	[5]	$ 0.11

[1] All quarters presented above were comprised of 13 weeks, except for the first quarter ended March 25, 2017, and the third quarter ended September 30, 2017, which were comprised of 12 and 14 weeks, respectively.

[2] 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 the fourth quarter of 2018 include charges related to the acquisition of Xcerra as follows - $37.8 million in restructuring charges comprised of $19.1 million of inventory end-of-manufacturing write-downs related to one of Xcerra's products, employee severance costs of $17.8 million and $0.9 million for other restructuring costs. We also recorded $13.1 million for the amortization of acquisition-related intangibles.

[3] Cost of sales is shown exclusive of the amortization of purchased intangible assets. Historically we have included the impact of the amortization of purchased intangible assets in cost of sales but have elected to show it separately on the face of our statement of operations. As a result, cost of sales amounts for 2017 and the first three quarters of 2018 have been adjusted to reflect this change. Amortization of purchased intangible amounts excluded from cost of sales were $0.87 million, $0.6 million, $0.7 million, and $0.7 million in the first, second, third, and fourth quarters of 2017, respectively, and $0.7 million, $0.7 million, $0.6 million, and $11.6 million in the first, second, third, and fourth quarters of 2018, respectively. See Note 1 "Summary of Significant Accounting Policies" for additional information on the reclassifications.

[4] Excludes amortization of $13,586, $2,689, and $5,170 for the years ended December 29, 2018, December 30, 2017, and December 31, 2016, respectively.

[5] 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.