Income Taxes - Effective Income Tax Rate Varied from Statutory Guernsey Tax Rate (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Schedule Of Effective Income Tax Rate Reconciliation [Line Items]
Releases of gross unrecognized tax benefits related to settled arrangements with tax authorities, change in measurement of certain positions and expiration of periods set forth in statutes of limitations			$ 40,644
Releases of gross unrecognized tax benefits	$ 26,842	$ 81,556
Tax Benefit Internal Structural Changes In Certain Jurisdictions			11,566
Net benefit from release of unrecognized tax benefit		47,770	16,232
Tax benefit change in measurement of deferred tax liability			9,236
Tax benefit from creation of deferred tax asset in certain jurisdiction		$ 17,465
Tax benefit related to the release of accrued withholding taxes on unremitted earnings	$ 18,504
Benefit of relating to changes in tax regulations in certain jurisdiction			3,142
ISRAEL
Schedule Of Effective Income Tax Rate Reconciliation [Line Items]
Tax benefit related to the release of accrued withholding taxes on unremitted earnings			$ 22,700

Net Benefit from Release of Unrecognized Tax Benefit

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Releases of Gross Unrecognized Tax Benefits

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Releases of gross unrecognized tax benefits related to settled arrangements with tax authorities, change in measurement of certain positions and expiration of periods set forth in statutes of limitations

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Schedule of Effective Income Tax Rate Reconciliation [Line Items]

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Tax Benefit Change in Measurement of Deferred Tax Liability

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Tax Benefit from Creation of Deferred Tax Asset in Certain Jurisdiction

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Tax Benefit Internal Structural Changes In Certain Jurisdiction

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deduction for extraterritorial income exclusion.

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