New Pronouncements - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jul. 01, 2012	Jun. 30, 2013	Jul. 01, 2012
New Accounting Pronouncement or Change in Accounting Principle, Retrospective Adjustments [Abstract]
Reclassification from accumulated other comprehensive income to investment income	$ 52,000	$ 977,000	$ 83,000	$ 1,071,000

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