Note 9 - Leases (Details Textual) $ in Millions	6 Months Ended
Jun. 29, 2019 USD ($)
Lessee, Operating Lease, Renewal Term	25 years
Finance Lease Right-of-use Asset, Accumulated Amortization	$ 0.1
Lessee, Sublease Income, Receivable, Remainder of Fiscal Year	0.1
Lessee, Sublease Income, Receivable, Year Two	$ 0.1
Minimum [Member]
Lessee, Lease, Remaining Term of Contract	1 year
Maximum [Member]
Lessee, Lease, Remaining Term of Contract	39 years

The amount of accumulated amortization of finance lease right-of-use asset.

No definition available.

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

- Definition

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.

+ References

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 remainder of the fiscal year.

+ References

No definition available.

+ Details

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

- 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

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=77888426&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: