Document And Entity Information Note To Financial Statement Details Textual statementsignificantaccountingpoliciespolicies statementnote1summaryofsignificantaccountingpoliciestables statementnote2businessacquisitionsgoodwillandotherpurchasedintangibleassetstables statementnote3financialinstrumentsmeasuredatfairvaluetables statementnote6discontinuedoperationstables statementnote8guaranteesandotherobligationstables statementnote1summaryofsignificantaccountingpoliciesreportedsharebasedcompensationdetails statementnote1summaryofsignificantaccountingpoliciescomputationofbasicanddilutedincomelosspersharedetails us-gaap_AvailableForSaleSecuritiesDebtSecurities Total estimated fair value statementnote1summaryofsignificantaccountingpoliciescustomerconcentrationdetails statementnote2businessacquisitionsgoodwillandotherpurchasedintangibleassetstotalpurchasepricedetails statementnote2businessacquisitionsgoodwillandotherpurchasedintangibleassetsfairvalueofcontingentconsiderationdetails statementnote2businessacquisitionsgoodwillandotherpurchasedintangibleassetspurchasepriceallocationdetails us-gaap_Revenues Revenues statementnote2businessacquisitionsgoodwillandotherpurchasedintangibleassetspreliminaryallocationofintangibleassetsdetails statementnote2businessacquisitionsgoodwillandotherpurchasedintangibleassetschangesincarryingvalueofgoodwilldetails statementnote2businessacquisitionsgoodwillandotherpurchasedintangibleassetspurchasedintangibleassetssubjecttoamortizationdetails statementnote3financialinstrumentsmeasuredatfairvalueshortterminvestmentsbysecuritytypedetails statementnote3financialinstrumentsmeasuredatfairvalueeffectivematuritiesofshortterminvestmentsdetails statementnote3financialinstrumentsmeasuredatfairvalueassetsmeasuredatfairvalueonrecurringbasisdetails us-gaap_AvailableForSaleSecurities Short-term investments statementnote6discontinuedoperationssummaryofoperatingresultsdetails statementnote8guaranteesandotherobligationschangesinaccruedwarrantydetails Notes To Financial Statements Inventory capitalized as property, plant and equipment Represents information about inventory capitalized as property, plant and equipment. Notes To Financial Statements [Abstract] Cash flows from investing activities, excluding effects from acquisitions: Short-term investments us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable Income taxes payable Money Market Funds [Member] Amortization of inventory step-up The amortization expense related to the stepped-up basis of inventory. Cash [Member] Cash and Cash Equivalents [Domain] us-gaap_IncreaseDecreaseInDeferredRevenue Deferred profit us-gaap_ComprehensiveIncomeNetOfTax Comprehensive income Cash and Cash Equivalents [Axis] Changes in other accrued liabilities us-gaap_IncreaseDecreaseInAccruedLiabilities Accrued compensation, warranty and other liabilities cohu_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfSharesAvailableForIssue Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Shares Available for Issue Represents share based compensation arrangement by share based payment award percentage of shares available for issue. Employee Stock Purchase Plan [Member] Employee stock purchase plan. Common stock, shares outstanding (in shares) us-gaap_PriorPeriodReclassificationAdjustment Prior Period Reclassification Adjustment us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity Line of Credit Facility, Maximum Borrowing Capacity New Accounting Pronouncements, Policy [Policy Text Block] us-gaap_IncreaseDecreaseInAccountsPayable Accounts payable Net sales Cash and cash equivalents Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period cohu_StandardProductWarrantyTerm Standard Product Warranty Term Describes the term of the product warranty. Percentage of net sales Customer Concentration Risk [Member] us-gaap_IncreaseDecreaseInOtherOperatingAssets Other current assets Concentration Risk Type [Domain] Concentration Risk Type [Axis] Sales Revenue, Net [Member] us-gaap_AllocatedShareBasedCompensationExpense Allocated share-based compensation Concentration Risk Benchmark [Domain] us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax Total share-based compensation, net Concentration Risk Benchmark [Axis] us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans Stock Issued During Period, Shares, Employee Stock Purchase Plans us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period us-gaap_IncreaseDecreaseInAccountsReceivable Accounts receivable Two Customers [Member] Information pertaining to two customers. us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Three Customers [Member] Information pertaining to three customers. us-gaap_LiabilitiesAndStockholdersEquity Retained earnings Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax us-gaap_IncreaseDecreaseInOtherNoncurrentAssets Changes in other assets us-gaap_IncreaseDecreaseInInventories Inventories us-gaap_NumberOfOperatingSegments Number of Operating Segments Segment Reporting, Policy [Policy Text Block] us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Foreign Currency Transactions and Translations Policy [Policy Text Block] cohu_PercentageOfRevenueRecognizedUponCustomerAcceptance Percentage of Revenue Recognized upon Customer Acceptance The percentage of revenue recognized upon customer acceptance. Raw materials and purchased parts Finished goods Earnings Per Share, Policy [Policy Text Block] Fair Value, Measurements, Recurring [Member] Work in process Comprehensive Income, Policy [Policy Text Block] Fair Value, Measurement Frequency [Domain] Measurement Frequency [Axis] Changes in current assets and liabilities, excluding effects from acquisitions: Discontinued Operations, Policy [Policy Text Block] us-gaap_ForeignCurrencyTransactionGainLossRealized Foreign Currency Transaction Gain (Loss), Realized Long-term Borrowings Assumed in Business Acquisition [Member] Long-term borrowings that were assumed by the reporting entity as the result of a business acquisition. Business Combination, Goodwill, and Intangible Assets Disclosure [Text Block] The entire disclosure for a business combination (or series of individually immaterial business combinations) completed during the period, including background, timing, and recognized assets and liabilities and the entire disclosure for the aggregate amount of goodwill and a description of intangible assets. us-gaap_OperatingIncomeLoss Income from operations us-gaap_DeferredIncomeTaxExpenseBenefit Deferred income taxes Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Amendment Flag Common stock, $1 par value; 60,000 shares authorized, 28,213 shares issued and outstanding in 2017 and 26,842 shares in 2016 Cost of sales Pension and Other Postretirement Plans, Policy [Policy Text Block] Warranty expense accruals Warranty liability assumed us-gaap_ProductWarrantyAccrualPayments Warranty payments Common stock, shares authorized (in shares) Common stock, shares issued (in shares) Other assets Common stock, par value (in dollars per share) Share-based compensation expense Fair Value, Measurement Inputs, Disclosure [Text Block] Current Fiscal Year End Date Document Fiscal Period Focus Document Fiscal Year Focus Document Period End Date Preferred stock, $1 par value; 1,000 shares authorized, none issued Remaining Useful Life (Year) Preferred stock, shares issued (in shares) Document Type us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent Other comprehensive income, net of tax Depreciation and amortization Preferred stock, shares authorized (in shares) Schedule of Product Warranty Liability [Table Text Block] Document Information [Line Items] Document Information [Table] Preferred stock, par value (in dollars per share) us-gaap_AssetsCurrent Total current assets Entity Filer Category Entity Current Reporting Status Schedule of Finite-Lived Intangible Assets [Table Text Block] Entity Voluntary Filers Entity Well-known Seasoned Issuer us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges (Gain) loss on disposal of assets Mark to market adjustment to Kita contingent consideration liability Customers individually accounting for more than 10% of net sales Represents the number of major customers accounting for 10% or more of the specified concentration risk benchmark, which includes, but not limited to, sales revenue, accounts receivable, etc. Adjustments to reconcile net income to net cash provided by operating activities: Entity Central Index Key Broadcast Microwave Services, Inc. (“BMS”) [Member] Represents information about Broadcast Microwave Services,Inc., the Company's microwave communications equipment segment. Entity Registrant Name Entity [Domain] us-gaap_AssetsFairValueDisclosure Legal Entity [Axis] cohu_DisposalGroupIncludingDiscontinuedOperationContingentConsideration Disposal Group, Including Discontinued Operation, Contingent Consideration Maximum amount of contingent consideration receivable for the disposal of assets and liabilities, including discontinued operation. Other current assets Entity Common Stock, Shares Outstanding (in shares) Paid-in capital us-gaap_CashAndCashEquivalentsFairValueDisclosure Cash and cash equivalents us-gaap_InventoryNet Stockholders' equity: Revenue Recognition, Policy [Policy Text Block] Trading Symbol Interest and other, net us-gaap_StockholdersEquity Total stockholders' equity Certificates of Deposit [Member] Goodwill and Intangible Assets, Policy [Policy Text Block] US Treasury Securities [Member] US Government-sponsored Enterprises Debt Securities [Member] Inventories: Accounts receivable, net Schedules of Concentration of Risk, by Risk Factor [Table Text Block] Cash flows from operating activities: us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent Allowance for Doubtful Accounts Receivable, Current Statement [Line Items] Cost and expenses: us-gaap_CostsAndExpenses us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax Change in unrealized gain/loss on investments us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax Adjustments related to postretirement benefits Current assets: Adjustments for New Accounting Principle, Early Adoption [Member] us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash provided by (used in) financing activities us-gaap_ProductWarrantyAccrual Balance at beginning of period Balance at end of period Foreign currency translation adjustments us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash used in investing activities us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash provided by operating activities us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease Net increase (decrease) in cash and cash equivalents Effect of exchange rate changes on cash and cash equivalents Other comprehensive income, net of tax: Business Acquisition, Acquiree [Domain] Business Acquisition [Axis] Noncurrent deferred gain on sale of facility us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High Type of Adoption [Domain] Adjustments for New Accounting Pronouncements [Axis] us-gaap_DeferredRevenue Deferred Revenue us-gaap_PaymentsOfDividendsCommonStock Cash dividends paid us-gaap_LoansPayableToBank Loans Payable to Bank Issuance (repurchases) of common stock, net Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 3 [Member] us-gaap_LineOfCredit Long-term Line of Credit Fair Value Hierarchy [Domain] Fair Value, Hierarchy [Axis] Cash dividends declared per share (in dollars per share) Equity Component [Domain] Concentration Risk, Credit Risk, Policy [Policy Text Block] Equity Components [Axis] us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis Total amortized cost Short-term borrowings us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding (in shares) Diluted (in shares) us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet Net assets acquired Effect of dilutive securities (in shares) Commitments Contingencies and Guarantees [Text Block] Gross Unrealized Losses Gross Unrealized Gains us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities Liabilities assumed Amortized Cost us-gaap_EarningsPerShareDiluted Net income (in dollars per share) Income (loss) from discontinued operations (in dollars per share) us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare Income from continuing operations (in dollars per share) us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare us-gaap_IncomeLossFromContinuingOperationsPerBasicShare Income from continuing operations (in dollars per share) Diluted: Weighted average common shares (in shares) Basic (in shares) Balance Sheet Location [Domain] us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets Total assets acquired us-gaap_EarningsPerShareBasic Net income (in dollars per share) Balance Sheet Location [Axis] us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare Income (loss) from discontinued operations (in dollars per share) us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment Property, plant and equipment Selling, General and Administrative Expenses [Member] Scenario, Unspecified [Domain] us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets Other assets Basic: Scenario [Axis] us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles Intangible assets subject to amortization us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets Current assets, including cash received us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Cost of Sales [Member] Income Statement Location [Domain] us-gaap_BusinessCombinationConsiderationTransferred1 Total purchase price Income Statement Location [Axis] Research and Development Expense [Member] Maximum [Member] Basis of Accounting, Policy [Policy Text Block] Range [Domain] Minimum [Member] Fair value of contingent consideration Customer [Axis] Significant Accounting Policies [Text Block] Range [Axis] Accounting Policies [Abstract] Customer [Domain] Statement of Financial Position [Abstract] Due in one year or less, estimated fair value us-gaap_BusinessCombinationContingentConsiderationLiability Balance for contingent consideration Balance for contingent consideration Statement of Cash Flows [Abstract] us-gaap_RepaymentsOfBankDebt Repayments of long-term debt Due in one year or less, amortized cost us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss Operating loss before income taxes Investments Classified by Contractual Maturity Date [Table Text Block] us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation Income tax provision us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue Net sales Disposal Group Name [Domain] Disposal Group Name [Axis] us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax Loss before taxes Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Disposal Groups, Including Discontinued Operations [Table Text Block] us-gaap_OtherAccruedLiabilitiesNoncurrent Other accrued liabilities us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax Loss on disposal of microwave communications equipment business us-gaap_ProductWarrantyAccrualNoncurrent Product Warranty Accrual, Noncurrent Fair Value, Assets Measured on Recurring Basis [Table Text Block] us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax Gain (loss) from disposal of segment Trade Names [Member] us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments Income from continuing operations before taxes Deferred income taxes us-gaap_EffectiveIncomeTaxRateContinuingOperations Effective Income Tax Rate Reconciliation, Percent Accrued retirement benefits Income tax provision Dividends declared but not yet paid us-gaap_PolicyTextBlockAbstract Accounting Policies Corporate Debt Securities [Member] cohu_BusinessCombinationContingentConsiderationArrangementsForeignCurrencyTranslationGainLoss Impact of currency exchange The amount increase (decrease) in the value of foreign currency translation gain (loss) of a contingent consideration. Foreign Government Debt Securities [Member] Settlement of contingent consideration Amount of increase (decrease) in the settlement value of a contingent consideration. Credit Facility [Domain] Available-for-sale Securities [Table Text Block] Statement [Table] Revolving Credit Facility [Member] Order or Production Backlog [Member] Credit Facility [Axis] Noncompete Agreements [Member] Cash flows from financing activities: Income Statement [Abstract] Noncurrent income tax liabilities Developed Technology Rights [Member] Award Date [Domain] Class of Stock [Axis] Award Type [Axis] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Award Date [Axis] Equity Award [Domain] Long-term debt, excluding current installments Customer Relationships [Member] Finite-Lived Intangible Assets, Major Class Name [Domain] Non-current Other Accrued Liabilities [Member] Represents non-current other accrued liabilities. Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block] Finite-Lived Intangible Assets by Major Class [Axis] us-gaap_ProceedsFromDivestitureOfBusinesses Proceeds from Divestiture of Businesses Schedule of Business Acquisitions by Acquisition, Contingent Consideration [Table Text Block] us-gaap_LiabilitiesCurrent Total current liabilities us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired Cash paid for Kita, net of cash received us-gaap_GoodwillAndIntangibleAssetImpairment Goodwill and Intangible Asset Impairment Cash paid to Kita shareholders Impact of currency exchange us-gaap_OtherDeferredCreditsCurrent Other Deferred Credits, Current Additions, net Schedule of Business Acquisitions, by Acquisition [Table Text Block] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms Kita Manufacturing Co. LTD. and Kita USA, Inc. [Member] Represents a business acquired by the reporting entity. us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding Contingencies Disclosure [Text Block] Current installments of long-term debt Loans Payable to Bank, Current us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Income Tax Disclosure [Text Block] Sales and maturities of short-term investments us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Vest on the Third Anniversary of Awards Grant [Member] Represent awards that are versing on the third anniversary of grant. us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Vest on the Second and Third Anniversary of Awards Grant [Member] Represent awards that are versing on the second and third anniversary of grant. us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1 Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price us-gaap_BusinessCombinationAcquisitionRelatedCosts Business Combination, Acquisition Related Costs us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Income taxes payable us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2 Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Due after one year through three years, estimated fair value Fair value of available-for-sale debt securities maturing in the second fiscal year through the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Due after one year through three years, amortized cost Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the third fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Accounts payable Accrued compensation and benefits Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Finite-lived intangible assets, average useful life (Year) Awards Granted in 2017 and 2016 [Member] Information pertaining to awards granted in 2017 and 2016. Finite-lived intangible assets, estimated fair value us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Awards Granted in 2015 [Member] Information pertaining to awards granted in 2015. Accrued warranty Other accrued liabilities us-gaap_AmortizationOfIntangibleAssets Amortization of Intangible Assets Weighted average shares used in computing income (loss) per share: us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Current liabilities: Schedule of Goodwill [Table Text Block] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant us-gaap_Assets us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent us-gaap_PaymentsToAcquireShortTermInvestments Purchases of short-term investments us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage us-gaap_PaymentsToAcquirePropertyPlantAndEquipment Purchases of property, plant and equipment us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1 Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Vesting [Domain] Net income Net income Cash received from sale of fixed assets Plan Name [Axis] Selling, general and administrative Vesting [Axis] Income (loss) from discontinued operations Loss, net of tax cohu_PercentageOfRevenueRecognizedUponShipmentAndPassageOfTitle Percentage of Revenue Recognized upon Shipment and Passage of Title The percentage of revenue recognized upon shipment and passage of title. Plan Name [Domain] us-gaap_IncomeLossFromContinuingOperations Income from continuing operations Property, plant and equipment purchases included in accounts payable Standby Letters of Credit [Member] Performance Shares [Member] Restricted Stock Units (RSUs) [Member] Intangible assets, net us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense Income tax benefit Antidilutive Securities, Name [Domain] Employee Stock Option [Member] Accumulated Amortization Gross Carrying Amount Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Antidilutive Securities [Axis] Research and development Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Statement of Comprehensive Income [Abstract] Supplemental disclosure of cash flow information: Cash paid for income taxes Investments [Domain] Investment Type [Axis] Goodwill Goodwill Beginning balance Ending balance us-gaap_PropertyPlantAndEquipmentNet Net property, plant and equipment Deferred profit The carrying value of deferred revenue, net of expenses, as of the balance sheet date that is expected to be recognized as such within one year or the normal operating cycle, if longer. us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment Less accumulated depreciation and amortization us-gaap_PropertyPlantAndEquipmentGross Debt Instrument [Axis] Debt Instrument, Name [Domain] Machinery and equipment Buildings and building improvements us-gaap_DebtInstrumentInterestRateStatedPercentage Debt Instrument, Interest Rate, Stated Percentage Land and land improvements us-gaap_TableTextBlock Notes Tables Property, plant and equipment, at cost: