Note 12 - Related Party Transactions (Details Textual)	12 Months Ended
Dec. 30, 2017
Blackrock [Member]
Ownership Percentage of the Company	13.10%

The percentage of ownership of common stock or equity of the company.

No definition available.

Name:	cohu_OwnershipPercentageOfTheCompany
Namespace Prefix:	cohu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration