Note 3 - Purchased Intangible Assets, Subject to Amortization (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 26, 2016	Dec. 26, 2015
Rasco Technology [Member]
Gross Carrying Amount	$ 27,371	$ 26,904
Accumulated Amortization	$ 25,018	23,776
Remaining Useful Life	255 days
Ismeca Technology [Member]
Gross Carrying Amount	$ 27,294	27,043
Accumulated Amortization	$ 11,269	10,329
Remaining Useful Life	4 years 292 days
Trade Names [Member]
Gross Carrying Amount	$ 5,614	5,547
Accumulated Amortization	$ 212	92
Remaining Useful Life	14 years 182 days
Gross Carrying Amount	$ 60,279	59,494
Accumulated Amortization	$ 36,499	$ 34,197

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.

No definition available.

+ Details

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

- Definition

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

+ References

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=66006027&loc=d3e16323-109275

+ Details

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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

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant

- Details

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Balance Type:
Period Type:

- Details

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

- Details

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Data Type:	na
Balance Type:
Period Type: