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Goodwill and Other Purchased Intangible Assets - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 28, 2015
Mar. 29, 2014
Dec. 27, 2014
Indefinite-lived Intangible Assets [Line Items]      
Amortization expense related to purchased intangible assets $ 1.8us-gaap_AmortizationOfIntangibleAssets $ 2.1us-gaap_AmortizationOfIntangibleAssets  
Trade Name [Member] | Rasco Technology [Member]      
Indefinite-lived Intangible Assets [Line Items]      
Amounts excluded related to trade names 1.9us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill
/ us-gaap_BusinessAcquisitionAxis
= cohu_RascoTechnologyMember
/ us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_TradeNamesMember		   2.1us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill
/ us-gaap_BusinessAcquisitionAxis
= cohu_RascoTechnologyMember
/ us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_TradeNamesMember
Trade Name [Member] | Ismeca [Member]      
Indefinite-lived Intangible Assets [Line Items]      
Amounts excluded related to trade names $ 3.7us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill
/ us-gaap_BusinessAcquisitionAxis
= cohu_IsmecaSemiconductorHoldingSaMember
/ us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_TradeNamesMember		   $ 3.6us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill
/ us-gaap_BusinessAcquisitionAxis
= cohu_IsmecaSemiconductorHoldingSaMember
/ us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_TradeNamesMember