New Pronouncements - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassification from accumulated other comprehensive income to investment income	$ 31	$ 94

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