Note 14 - Discontinued Operations (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Dec. 28, 2019	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Disposal Group, Including Discontinued Operation, Impairment		$ (0)	$ 1,086	$ (0)
Fixtures Services Business FSG [Member]
Disposal Group, Including Discontinued Operation, Impairment	$ 1,100

Amount of impairment attributable to disposal group, including, but not limited to, discontinued operation.

No definition available.

Name:	cohu_DisposalGroupIncludingDiscontinuedOperationImpairment
Namespace Prefix:	cohu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration