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Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Apr. 30, 2015 | Apr. 30, 2015 | Jan. 31, 2014 | Jan. 31, 2015 | Apr. 30, 2014 | Oct. 31, 2015
Taxes [Line Items] |  |  |  |  |  |
Statutory federal income tax rate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate |  |  |  |
Gross unrecognized tax benefits | $ 129.9 us-gaap_UnrecognizedTaxBenefits | $ 129.9 us-gaap_UnrecognizedTaxBenefits |  |  |  |
Unrecognized tax benefits that would affect effective tax rate | 129.9 us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate | 129.9 us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate |  |  |  |
Estimated potential decrease in underlying unrecognized tax benefits, minimum | 0 us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleEstimatedRangeOfChangeLowerBound | 0 us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleEstimatedRangeOfChangeLowerBound |  |  |  |
Estimated potential decrease in underlying unrecognized tax benefits, maximum | 37 us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleEstimatedRangeOfChangeUpperBound | 37 us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleEstimatedRangeOfChangeUpperBound |  |  |  |
Fiscal Year 2012 | IRS |  |  |  |  |  |
Taxes [Line Items] |  |  |  |  |  |
Unrecognized tax benefits decrease resulting from settlement |  |  | 10.0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxPeriodAxis = snps_FiscalYearTwentyTwelveMember |  |  |
Fiscal Year 2012 | Taiwan |  |  |  |  |  |
Taxes [Line Items] |  |  |  |  |  |
Unrecognized tax benefits decrease resulting from settlement |  |  |  | 1.1 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities / us-gaap_IncomeTaxAuthorityAxis = country_TW / us-gaap_TaxPeriodAxis = snps_FiscalYearTwentyTwelveMember |  |
Fiscal Year 2009 and 2010 | Taiwan |  |  |  |  |  |
Taxes [Line Items] |  |  |  |  |  |
Unrecognized tax benefits decrease resulting from settlement |  |  |  |  | 5.1 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities / us-gaap_IncomeTaxAuthorityAxis = country_TW / us-gaap_TaxPeriodAxis = snps_FiscalYearTwentyZeroNineAndTwentyTenMember |
Tax Adjustments, Settlements, and Unusual Provisions |  |  |  |  | 3.9 us-gaap_TaxAdjustmentsSettlementsAndUnusualProvisions / us-gaap_IncomeTaxAuthorityAxis = country_TW / us-gaap_TaxPeriodAxis = snps_FiscalYearTwentyZeroNineAndTwentyTenMember |
Forecast |  |  |  |  |  |
Taxes [Line Items] |  |  |  |  |  |
Expected research tax credit benefit |  |  |  |  |  | $ 12.4 snps_IncomeTaxRateReconciliationEstimatedResearchTaxCreditBenefitAmount / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember

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- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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- Definition Amount of (increase) decrease reasonably possible in the estimated lower bound of the unrecognized tax benefit for a tax position taken or expected to be taken. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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- Definition Amount of (increase) decrease reasonably possible in the estimated upper bound of the unrecognized tax benefit for a tax position taken or expected to be taken. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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- Definition Amount of increase (decrease) to previously recorded tax expense. Includes, but is not limited to, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, and IRS tax settlement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28446-109314 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28511-109314 + Details
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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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