Note 10 - Discontinued Operations (Details Textual) $ in Millions	3 Months Ended
Dec. 28, 2019 USD ($)
Fixtures Services Business FSG [Member]
Disposal Group, Including Discontinued Operation, Impairment	$ 1.1

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