Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Jan. 30, 2022	Jul. 04, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-34218
Entity Registrant Name	COGNEX CORP
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
Title of 12(b) Security	Common Stock, par value $.002 per share
Trading Symbol	CGNX
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Small Business	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 14,919,879,186
Entity Common Stock, Shares Outstanding		173,915,951
Entity Central Index Key	0000851205
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false