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Stock-based Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021 | Dec. 14, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-Based Payment Arrangement, Expense | $ 14.1 | $ 11.1 | $ 9.9 |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 270,547 | 779,150 | 790,759 |  |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | $ 10.1 |  |  |  |
Weighted-average recognition period, Compensation expense related to stock awards not yet vested | 1 year 6 months |  |  |  |
Number of shares authorized under a Plan |  |  |  |  | 20,500,000
Shares available for future grants under a Plan | 3,874,846 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period | 10 years |  |  |  |
Share-based Compensation, Expected Forfeiture Rate | 2.00% |  |  |  |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | 3 years |  |  |  |
Settlement of performance-based restricted stock units, net of shares withheld for taxes | 367,315 | 301,864 | 251,981 |  |
Performance Shares [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Settlement of performance-based restricted stock units, net of shares withheld for taxes | 0 | 163,999 | 240,412 |  |
Performance Shares [Member] | Minimum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Performance Factor | 0.00% |  |  |  |
Performance Shares [Member] | Maximum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Performance Factor | 200.00% |  |  |  |
Market-Based Awards | Minimum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Performance Factor | 0.00% |  |  |  |
Market-Based Awards | Maximum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Performance Factor | 200.00% |  |  |  |
Employee Stock [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Number of shares authorized under a Plan |  |  |  | 5,800,000 |
Shares available for future grants under a Plan | 1,792,275 |  |  |  |
Price for shares offered under ESPP, as a percentage of closing price on the first or last day of the offering period | 85.00% |  |  |  |
Phantom Share Units (PSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | 3 years |  |  |  |
Settlement of performance-based restricted stock units, net of shares withheld for taxes | 156,585 | 156,012 | 162,969 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instrument Other than Option, Nonvested, Intrinsic Value | $ 21.70 |  |  |  |
Share-based compensation liability | $ 6.0 |  |  |  |

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