The increase in lease liability due to a lease modification.

No definition available.

Name:	cohu_LeaseLiabilityIncreaseDueToLeaseModification
Namespace Prefix:	cohu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The increase in right of use assets resulting from a lease modification.

No definition available.

Name:	cohu_RightOfUseAssetIncreaseDueToLeaseModification
Namespace Prefix:	cohu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of expected cost remaining for the specified restructuring cost.

No definition available.

Name:	us-gaap_RestructuringAndRelatedCostExpectedCostRemaining1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The number of positions eliminated during the period as a result of restructuring activities.

No definition available.

Name:	us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Number of additional shares authorized for issuance under share-based payment arrangement.

No definition available.

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PlanNameAxis=cohu_EquityIncentivePlan2005Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PlanNameAxis=cohu_EmployeeStockPurchasePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 13 - Subsequent Events (Details Textual) - Subsequent Event [Member] $ in Millions	May 08, 2019 shares	Apr. 30, 2019 USD ($)	Apr. 01, 2019 USD ($)
Restructuring and Related Cost, Number of Positions Eliminated		105
Lease Liability, Increase Due to Lease Modification			$ 5.6
Right of Use Asset, Increase Due to Lease Modification			$ 5.6
Equity Incentive Plan 2005 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized \| shares	2,000,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized \| shares	500,000
Minimum [Member]
Restructuring and Related Cost, Expected Cost Remaining		$ 7.8
Maximum [Member]
Restructuring and Related Cost, Expected Cost Remaining		$ 8.8