Cover Page	6 Months Ended
	Jun. 30, 2019 shares
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2019
Document Transition Report	false
Entity File Number	001-34218
Entity Registrant Name	COGNEX CORP
Entity Central Index Key	0000851205
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Incorporation, State or Country Code	MA
Entity Tax Identification Number	04-2713778
Entity Address, Address Line One	One Vision Drive
Entity Address, City or Town	Natick
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01760
City Area Code	508
Local Phone Number	650-3000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $.002 per share
Trading Symbol	CGNX
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding	170,660,621