Document and Entity Information (USD $)	6 Months Ended
	Jul. 03, 2011	Jul. 04, 2010
Document and Entity Information [Abstract]
Entity Registrant Name	COGNEX CORP
Entity Central Index Key	0000851205
Document Type	10-Q
Document Period End Date	Jul. 03, 2011
Amendment Flag	false
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float		$ 617,469,419
Entity Common Stock, Shares Outstanding	42,064,561