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Financial Instruments Measured at Fair Value - Short-Term Investments by Security Type (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 28, 2015
Dec. 27, 2014
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 1,110us-gaap_AvailableForSaleSecuritiesAmortizedCost $ 1,155us-gaap_AvailableForSaleSecuritiesAmortizedCost
Gross Unrealized Gains 0cohu_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments 0cohu_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments
Gross Unrealized Losses 0cohu_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments 0cohu_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
Estimated Fair Value 1,110us-gaap_AvailableForSaleSecuritiesCurrent 1,155us-gaap_AvailableForSaleSecuritiesCurrent [1]
Municipal Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 110us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_MunicipalBondsMember		 155us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_MunicipalBondsMember
Gross Unrealized Gains 0cohu_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_MunicipalBondsMember		 0cohu_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_MunicipalBondsMember
Gross Unrealized Losses 0cohu_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_MunicipalBondsMember		 0cohu_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_MunicipalBondsMember
Estimated Fair Value 110us-gaap_AvailableForSaleSecuritiesCurrent
/ us-gaap_InvestmentTypeAxis
= us-gaap_MunicipalBondsMember		 155us-gaap_AvailableForSaleSecuritiesCurrent
/ us-gaap_InvestmentTypeAxis
= us-gaap_MunicipalBondsMember
Bank Certificates of Deposit [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember		 1,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember
Gross Unrealized Gains 0cohu_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember		 0cohu_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember
Gross Unrealized Losses 0cohu_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember		 0cohu_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember
Estimated Fair Value $ 1,000us-gaap_AvailableForSaleSecuritiesCurrent
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember		 $ 1,000us-gaap_AvailableForSaleSecuritiesCurrent
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember
[1] Derived from December 27, 2014 audited financial statements