Disclosure - Restructuring (Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 29, 2025	Mar. 30, 2024
Restructuring Charges [Abstract]
Restructuring cost in cost of goods sold	$ 3,635	$ 788
RestructuringCost	4,758	1,046
Restructuring costs in operating expenses	$ 1,123	$ 258

Restructuring cost recored to cost of goods sold for inventory write-downs.

No definition available.

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