New Pronouncements - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
Sep. 29, 2013	Sep. 30, 2012	Sep. 29, 2013	Sep. 30, 2012
New Accounting Pronouncement Or Change In Accounting Principle Retrospective Adjustments [Abstract]
Reclassification from accumulated other comprehensive income to investment income	$ 20,000	$ 340,000	$ 103,000	$ 1,411,000

Other comprehensive income loss reclassification adjustment for realized gain loss on sale of securities included in net income, net of tax.

No definition available.

Name:	cgnx_OtherComprehensiveIncomeLossReclassificationAdjustmentForRealizedGainLossOnSaleOfSecuritiesIncludedInNetIncomeNetOfTax
Namespace Prefix:	cgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration