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Employee Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] |  |  |
Contributions by the Company to the plan | $ 14.0 | $ 13.2 | $ 11.3
Employer contribution, vesting period | 4 years | 4 years | 4 years

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- Definition Defined Contribution Plan, Employer Contribution, Vesting Period + References No definition available. + Details
Name: | ffiv_DefinedContributionPlanEmployerContributionVestingPeriod
Namespace Prefix: | ffiv_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration