Document and Entity Information	3 Months Ended
	Apr. 01, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	COGNEX CORP
Entity Central Index Key	0000851205
Document Type	10-Q
Document Period End Date	Apr. 01, 2012
Amendment Flag	false
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	42,835,011