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Stock-based Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Dec. 14, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Payment Arrangement, Expense	$ 15.1	$ 14.1	$ 11.1
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	368,384	270,547	779,150
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 11.0
Weighted-average recognition period, Compensation expense related to stock awards not yet vested	1 year 4 months 24 days
Number of shares authorized under a Plan					23,800,000
Shares available for future grants under a Plan	6,740,076
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Share-based Compensation, Expected Forfeiture Rate	2.00%
Share-Based Payment Arrangement, Expense, Tax Benefit	$ 3.6	$ 4.0	$ 2.3
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	283,026	367,315	301,864
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 7.3	$ 4.7	$ 4.7
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	0	163,999
Performance Shares [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Factor	0.00%
Performance Shares [Member] | Maximum
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
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				7,600,000
Shares available for future grants under a Plan	3,499,685
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	195,118	156,585	156,012
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instrument Other than Option, Nonvested, Intrinsic Value	$ 25.52
Share-based compensation liability	$ 5.7
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 2.5	$ 1.5	$ 0.1
Equity Option
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

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