Income Taxes - Effective Income Tax Rate Varied from Statutory Guernsey Tax Rate (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
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	$ 4,757	$ 7,701	$ 47,582
Tax (expense) benefit resulting from the release of valuation allowances on deferred tax assets	(1,211)	6,006	15,438
Foreign tax benefit from internal structural changes		10,933
Foreign tax expense for the estimated additional tax charge of gain from sale of a business	3,193	$ 39,596
Release of gross unrecognized tax benefits offset by a net benefit included within income tax expense			14,971
Foreign tax benefit resulting from tax enactments related to COVID-19			$ 4,964
Benefit of relating to changes in tax regulations in certain jurisdiction	8,871
ISRAEL
Schedule Of Effective Income Tax Rate Reconciliation [Line Items]
Tax benefit related to the release of accrued withholding taxes on unremitted earnings	$ 37,000

Income tax reconciliation foreign tax benefit from internal structural changes.

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Income tax reconciliation foreign tax expense for the estimated additional tax charge gain from sale of business.

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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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No definition available.

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Schedule of Effective Income Tax Rate Reconciliation [Line Items]

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Amount of deferred foreign income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Amount of current and deferred foreign income tax expense (benefit) attributable to income (loss) from continuing operations.

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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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Amount of increase (decrease) in unrecognized tax benefits attributable to uncertain tax positions taken in tax returns.

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