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Earnings per Share - EPS Reconciliation (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Numerator: |  |  |
Net income | $ 238.5 | $ 207.1 | $ 116.3
Less: Allocation to participating securities | (8.1) | (6.1) | (3.5)
Net income allocated to common stockholders | 230.4 | 201.0 | 112.8
Net income allocated to common stockholders | $ 230.4 | $ 201.0 | $ 112.8
Denominator: |  |  |
Common shares outstanding (in shares) | 19,957,333 | 19,570,403 | 19,130,643
Dilutive potential common shares outstanding: |  |  |
Share-based awards (in shares) | 662,007 | 497,137 | 547,525
Diluted shares outstanding (in shares) | 20,619,340 | 20,067,540 | 19,678,168
Earnings per share: |  |  |
Basic (in dollar per share) | $ 11.55 | $ 10.27 | $ 5.90
Diluted (in dollar per share) | $ 11.18 | $ 10.01 | $ 5.74
Common Stock Split |  |  |
Denominator: |  |  |
Common shares outstanding (in shares) | 29,936,000 | 29,355,605 | 28,695,965
Dilutive potential common shares outstanding: |  |  |
Share-based awards (in shares) | 993,011 | 745,706 | 821,288
Diluted shares outstanding (in shares) | 30,929,011 | 30,101,311 | 29,517,253
Earnings per share: |  |  |
Basic (in dollar per share) | $ 7.71 | $ 6.85 | $ 3.93
Diluted (in dollar per share) | $ 7.45 | $ 6.67 | $ 3.82

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