Earnings per Share - Schedule of Reconciliation of Numerator and Denominator of Diluted Earnings Per Share (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Numerator:
Net income	$ 63.4	$ 61.9	$ 220.2	$ 184.1
Less: Allocation to participating securities	(2.4)	(2.2)	(7.3)	(6.5)
Net income allocated to common stockholders, basic	61.0	59.7	212.9	177.6
Net income allocated to common stockholders, diluted	$ 61.0	$ 59.7	$ 212.9	$ 177.6
Denominator:
Common shares outstanding (in shares)	47,115,819	45,964,905	46,773,656	45,673,929
Dilutive potential common shares outstanding:
Share-based awards (in shares)	2,836,345	1,649,643	2,529,074	1,557,126
Diluted weighted-average common shares (in shares)	49,952,164	47,614,548	49,302,730	47,231,055

Denominator Basic

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Numerator Basic

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Undistributed Earnings Allocated to Participating Securities - Continuing Operations represents earnings from continuing operations allocated (not distributed) to participating securities under the two-class method to the extent that participating securities may share in earnings as if all of the earnings for the period had been distributed.

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Amount after tax of income (loss) from continuing operations attributable to the parent.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) from continuing operations available to common shareholders.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) from continuing operations available to common shareholders.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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