Note 9 - Leases (Details Textual) - USD ($)	9 Months Ended
Sep. 26, 2020	Dec. 28, 2019
Lessee, Operating Lease, Renewal Term (Year)	25 years
Finance Lease, Right-of-Use Asset, Accumulated Amortization	$ 26,000	$ 100,000
Lessee, Sublease Income, Receivable, Year Two	$ 100,000
Minimum [Member]
Lessee, Lease, Remaining Term of Contract (Year)	1 year
Maximum [Member]
Lessee, Lease, Remaining Term of Contract (Year)	37 years

Remaining term of lessee's operating and finance lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

No definition available.

+ Details

Name:	cohu_LesseeLeaseRemainingTermOfContract
Namespace Prefix:	cohu_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of sublease income receivable for the second fiscal year following the latest year.

+ References

No definition available.

+ Details

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

- Definition

Amount of accumulated amortization of right-of-use asset from finance lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918638-209977

+ Details

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

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseRenewalTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Details

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