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Warranties - Textual (Details) | 9 Months Ended
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Sep. 28, 2019
Product Warranties Disclosures [Abstract] |
Product warranty period | 12 months

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- Definition Product warranty period. + References No definition available. + Details
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Namespace Prefix: | onto_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_ProductWarrantiesDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration