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Derivative Instruments - Information Regarding Fair Value of Forward Contracts Outstanding (Detail) (USD $)
In Thousands, unless otherwise specified
Apr. 05, 2015
Dec. 31, 2014
Derivatives, Fair Value [Line Items]    
Derivative Asset $ 334us-gaap_DerivativeAssets $ 114us-gaap_DerivativeAssets
Derivative Liability 779us-gaap_DerivativeLiabilities 97us-gaap_DerivativeLiabilities
Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset 327us-gaap_DerivativeAssets
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
108us-gaap_DerivativeAssets
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Designated as Hedging Instrument | Accrued Expenses    
Derivatives, Fair Value [Line Items]    
Derivative Liability 762us-gaap_DerivativeLiabilities
/ us-gaap_BalanceSheetLocationAxis
= cgnx_AccruedExpensesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
84us-gaap_DerivativeLiabilities
/ us-gaap_BalanceSheetLocationAxis
= cgnx_AccruedExpensesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Not Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset 7us-gaap_DerivativeAssets
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
6us-gaap_DerivativeAssets
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Not Designated as Hedging Instrument | Accrued Expenses    
Derivatives, Fair Value [Line Items]    
Derivative Liability $ 17us-gaap_DerivativeLiabilities
/ us-gaap_BalanceSheetLocationAxis
= cgnx_AccruedExpensesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
$ 13us-gaap_DerivativeLiabilities
/ us-gaap_BalanceSheetLocationAxis
= cgnx_AccruedExpensesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember