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Segment Disclosure - Additional information (Detail) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jan. 31, 2019 Segment Customer | Jan. 31, 2018 Customer | Oct. 31, 2018 Segment
Segment Reporting Information [Line Items] |  |  |
Number of reportable operating segment | Segment | 2 |  | 1
Customer concentration risk | Sales revenue |  |  |
Segment Reporting Information [Line Items] |  |  |
Number of major customers | Customer | 1 | 1 |

X
- Definition Number of major customers. + References No definition available. + Details
Name: | snps_NumberOfMajorCustomers
Namespace Prefix: | snps_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueNetMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |