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Retirement Plans - Defined Contribution Retirement Plans - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, employer discretionary contribution amount | $ 27.1 | $ 23.3 | $ 19.2
United States | 401k Plan | First Matching Contributions |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, employer matching contribution, percent of employees' gross pay (as a percent) | 100.00% |  |
Defined contribution plan, employers matching contribution, annual vesting percentage (as a percent) | 3.00% |  |
United States | 401k Plan | Second Matching Contributions |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, employer matching contribution, percent of employees' gross pay (as a percent) | 50.00% |  |
Defined contribution plan, employers matching contribution, annual vesting percentage (as a percent) | 4.00% |  |
United Kingdom |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, employers matching contribution, annual vesting percentage (as a percent) | 100.00% |  |
Minimum | United States | 401k Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, annual contributions per employee, percent (as a percent) | 1.00% |  |
Maximum | United States | 401k Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, annual contributions per employee, percent (as a percent) | 80.00% |  |
Defined contribution plan, employers matching contribution, annual vesting percentage (as a percent) | 7.00% |  |
Maximum | United Kingdom |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, employer matching contribution, percent of employees' gross pay (as a percent) | 10.00% |  |

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- Definition Defined Contribution Plan, Annual Contributions Per Employee, Percent + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480794/715-70-50-1 + Details
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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Definition Percentage of employer's matching contributions to a defined contribution plan that vests in a given year. + References No definition available. + Details
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- Details
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