Accumulated Other Comprehensive Loss Textual (Additional Information) (Details) - USD ($)	12 Months Ended
Dec. 28, 2024	Dec. 30, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Loss [Abstract]
tax effects in other comprehensive (loss)	$ (36,800)	$ 900,000	$ (700)

tax effects on net income of amounts recorded in other comprehensive income (loss)

No definition available.

Name:	onto_TaxEffectsInOtherComprehensiveLoss
Namespace Prefix:	onto_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration