Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount

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Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Provisional Income Tax Expense (Benefit)

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Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Transition Tax For Accumulated Foreign Earnings, Provisional Income Tax Expense

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Tax Cuts And Jobs Act of 2017, Incomplete Accounting, Transition Tax For Accumulated Foreign Earnings, Provisional Liability

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Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Transition Tax for Accumulated Foreign Earnings, Provisional Income Tax Expense

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Taxes [Line Items]

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards classified as noncurrent.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Estimated amount of loss resulting from an adverse tax position.

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The sum of the amounts of estimated penalties and interest recognized in the period arising from income tax examinations.

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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.

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Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended
Taxes - Additional Information (Detail) - USD ($)	Jul. 31, 2017	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	Oct. 31, 2018	Oct. 31, 2017	Jan. 31, 2017	Nov. 01, 2016
Taxes [Line Items]
Increase in income tax expense as result of the Tax Cuts and Jobs Act				$ 119,000,000
Provisional tax charge as result of deferred tax remeasurement due to Tax Cuts and Jobs Act				46,000,000
Provisional transition tax expense as result of the Tax Cuts and Jobs Act				71,000,000
Income taxes payable on foreign earnings as result of the Tax Cuts and Jobs Act			$ 18,000,000	78,000,000
Deferred income taxes		$ 167,427,000				$ 167,427,000			$ 243,989,000
Share-based compensation, excess tax benefit, amount		14,600,000			$ 18,400,000	25,400,000	$ 29,700,000
Minimum
Taxes [Line Items]
Estimated potential decrease in underlying unrecognized tax benefits		0				0
Maximum
Taxes [Line Items]
Estimated potential decrease in underlying unrecognized tax benefits		$ 13,000,000				$ 13,000,000
Accounting Standards Update 2016-09 \| New Accounting Pronouncement, Early Adoption, Effect
Taxes [Line Items]
Deferred income taxes										$ 106,500,000
Retained Earnings \| Accounting Standards Update 2016-09 \| New Accounting Pronouncement, Early Adoption, Effect
Taxes [Line Items]
Cumulative effect adjustment											$ 106,500,000
State
Taxes [Line Items]
Provisional transition tax expense as result of the Tax Cuts and Jobs Act				$ 2,000,000
Foreign Tax Authority \| Fiscal Year 2014 \| KOREA, REPUBLIC OF
Taxes [Line Items]
Settlement of transfer pricing issue expense (benefit)					(10,900,000)
Foreign Tax Authority \| Fiscal years 2012 to 2016 \| KOREA, REPUBLIC OF
Taxes [Line Items]
Settlement of transfer pricing issue expense (benefit)					$ 7,900,000
Synopsys Hungary \| Foreign Tax Authority \| Tax Year 2011 - Tax Year 2013 \| Hungarian Tax Authority
Taxes [Line Items]
Estimate of tax assessment	$ 47,000,000
Estimate of additional penalties and interest	18,000,000
Synopsys Hungary \| Foreign Tax Authority \| Fiscal Year 2015 and Beyond \| Hungarian Tax Authority
Taxes [Line Items]
Estimate of tax assessment	$ 18,000,000
Scenario, Forecast
Taxes [Line Items]
Statutory federal income tax rate								23.40%