Accumulated Other Comprehensive Income (Loss) - Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 28, 2025	Jun. 29, 2024
Accumulated Other Comprehensive Loss [Abstract]
Tax Effect Marketable Securities	$ 64	$ 236

tax effects on net income of amounts recorded in other comprehensive loss for net unrealized losses on available-for-sale marketable securities.

No definition available.

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