Percentage of quarterly installments of the original principal, with balance payable at maturity.

No definition available.

Name:	cohu_DebtInstrumentAmortizationPercentageOfPrincipalAmount
Namespace Prefix:	cohu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of available lines of credit as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	cohu_NumberOfAvailableLinesOfCredit
Namespace Prefix:	cohu_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Period of time between issuance and maturity of debt instrument, 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_DebtInstrumentTerm
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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
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+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Details

Name:	dei_LegalEntityAxis=cohu_IsmecaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cohu_SecuredTermLoanFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cohu_KitaTermLoansMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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

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

- Details

Name:	us-gaap_DebtInstrumentAxis=cohu_XcerraTermLoanMember
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Data Type:	na
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Period Type:

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Note 3 - Borrowings and Credit Agreements (Details Textual) $ in Thousands, € in Millions, SFr in Millions			9 Months Ended
	Jul. 26, 2019 EUR (€)	Oct. 01, 2018 USD ($)	Sep. 28, 2019 USD ($)	Sep. 28, 2019 CHF (SFr)	Dec. 29, 2018 USD ($)
Long-term Debt, Current Maturities, Total			$ 6,382		$ 6,676
Long-term Line of Credit, Total			3,241		3,115
Ismeca [Member]
Line of Credit Facility, Maximum Borrowing Capacity \| SFr				SFr 2
Long-term Line of Credit, Total			$ 0		$ 0
Number of Available Lines of Credit			1	1
Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity			$ 8,900
Long-term Line of Credit, Total			3,300
Secured Term Loan Facility [Member]
Debt Instrument, Face Amount		$ 350,000
Debt Instrument, Amortization, Percentage of Principal Amount		0.25%
Long-term Debt, Total			338,800
Long-term Debt, Current Maturities, Total			2,400
Long-term Debt, Fair Value			332,200
Secured Term Loan Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate		3.00%
Kita Term Loans [Member]
Long-term Debt, Total			4,000
Long-term Debt, Current Maturities, Total			$ 500
Kita Term Loans [Member] \| Minimum [Member]
Debt Instrument, Interest Rate, Stated Percentage			0.05%	0.05%
Kita Term Loans [Member] \| Maximum [Member]
Debt Instrument, Interest Rate, Stated Percentage			0.44%	0.44%
Xcerra Term Loan [Member]
Long-term Debt, Total			$ 1,500
Long-term Debt, Current Maturities, Total			$ 300
Debt Instrument, Interest Rate, Stated Percentage			2.35%	2.35%
Debt Instrument, Term			10 years
Rasco Term Loan [Member]
Debt Instrument, Face Amount \| €	€ 3.4
Long-term Debt, Total			$ 3,700
Long-term Debt, Current Maturities, Total			$ 0
Debt Instrument, Interest Rate, Stated Percentage	0.80%
Debt Instrument, Term	10 years