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

The period of principal payments pursuant to the debt agreement.

+ References

No definition available.

+ Details

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Namespace Prefix:	cohu_
Data Type:	xbrli:durationItemType
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

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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.

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

- Definition

Amount of assets pledged to secure a debt instrument.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

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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

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

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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

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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.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-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

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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

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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Name:	us-gaap_DebtInstrumentAxis=cohu_KitaTermLoansMember
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Note 3 - Borrowings and Credit Agreements (Details Textual) $ in Thousands, € in Millions, SFr in Millions					6 Months Ended
	Jun. 16, 2020 EUR (€)	Aug. 01, 2019 EUR (€)	Jul. 26, 2019 EUR (€)	Oct. 01, 2018 USD ($)	Jun. 27, 2020 USD ($)	Jun. 27, 2020 EUR (€)	Jun. 29, 2019 USD ($)	Jun. 27, 2020 EUR (€)	Jun. 27, 2020 CHF (SFr)	Dec. 28, 2019 USD ($)
Long-term Debt, Current Maturities, Total					$ 7,919					$ 6,517
Long-term Debt, Fair Value					327,500
Proceeds from Issuance of Long-term Debt, Total					4,345		$ 0
Long-term Line of Credit, Total					4,665					3,195
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	1
Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity					$ 9,000
Long-term Line of Credit, Total					4,700
Secured Term Loan Facility [Member]
Debt Instrument, Face Amount				$ 350,000
Debt Instrument, Amortization, Percentage of Principal Amount				0.25%
Long-term Debt, Total					337,900					339,100
Long-term Debt, Current Maturities, Total					2,300					2,300
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					3,700					3,800
Long-term Debt, Current Maturities, Total					$ 300					400
Kita Term Loans [Member] \| Minimum [Member]
Debt Instrument, Interest Rate, Stated Percentage					0.05%			0.05%	0.05%
Kita Term Loans [Member] \| Maximum [Member]
Debt Instrument, Interest Rate, Stated Percentage					0.40%			0.40%	0.40%
Xcerra Term Loan [Member]
Long-term Debt, Total					$ 1,300					1,500
Long-term Debt, Current Maturities, Total					$ 300					300
Debt Instrument, Interest Rate, Stated Percentage					2.35%			2.35%	2.35%
Debt Instrument, Term (Year)					10 years	10 years
Loan Facilities [Member] \| Construction Loans [Member]
Debt Instrument, Face Amount \| €			€ 8.6
Long-term Debt, Total					$ 8,400					5,500
Long-term Debt, Current Maturities, Total					$ 400					$ 300
First Facility [Member] \| Construction Loans [Member]
Debt Instrument, Interest Rate, Stated Percentage		0.80%
Debt Instrument, Term (Year)		10 years	10 years
Debt Instrument, Collateral Amount \| €			€ 3.4
Proceeds from Issuance of Long-term Debt, Total \| €		€ 3.4
Debt Instrument, Principal Payment Terms (Year)		8 years
Second Facility [Member] \| Construction Loans [Member]
Debt Instrument, Interest Rate, Stated Percentage					1.05%			1.05%	1.05%
Debt Instrument, Term (Year)			15 years		15 years	15 years
Debt Instrument, Collateral Amount \| €			€ 5.2
Proceeds from Issuance of Long-term Debt, Total \| €						€ 4.1
Debt Instrument, Principal Payment Terms (Year)					15 years	15 years
Debt Instrument, Unused Borrowing Capacity, Amount \| €								€ 1.1
Third Facility [Member] \| Construction Loans [Member]
Debt Instrument, Face Amount \| €	€ 1.5
Debt Instrument, Interest Rate, Stated Percentage					1.20%			1.20%	1.20%
Debt Instrument, Term (Year)	10 years				10 years	10 years
Debt Instrument, Collateral Amount \| €			€ 1.5
Proceeds from Issuance of Long-term Debt, Total					$ 0