Goodwill and Other Purchased Intangible Assets - Purchased Intangible Assets, Subject to Amortization (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 28, 2015	Dec. 27, 2014
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 54,448	$ 56,859
Accumulated Amortization	29,040	29,495
Rasco Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	26,697	29,845
Accumulated Amortization	21,090	22,616
Remaining Useful Life	1 year 9 months 18 days
Ismeca Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	27,751	27,014
Accumulated Amortization	$ 7,950	$ 6,879
Remaining Useful Life	5 years 9 months 18 days

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

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

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=cohu_IsmecaTechnologyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=cohu_RascoTechnologyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: