Document and Entity Information - shares	9 Months Ended
	Sep. 28, 2019	Nov. 01, 2019
Cover [Abstract]
Entity Registrant Name	Onto Innovation Inc.
Entity Central Index Key	0000704532
Document Type	10-Q
Document Period End Date	Sep. 28, 2019
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	ONTO
Current Fiscal Year End Date	--12-28
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $0.001 par value per share
Security Exchange Name	NYSE
Entity File Number	000-39110
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	16 Jonspin Road
Entity Address, City or Town	Wilmington
Entity Address, State or Province	MA
City Area Code	978
Local Phone Number	253-6200
Entity Address, Postal Zip Code	01887
Entity Tax Identification Number	94-2276314
Document Quarterly Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		50,062,039