Stock-based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)	3 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)	1,500,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Shares Deferred (in shares)	79,815
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.00%	0.00%	0.00%
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 8.7
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 9 months 18 days
Performance-contingent Restricted Share Units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	103,780
Granted, weighted average grant date fair value (in dollars per share)	$ 76.52
Performance-contingent Restricted Share Units | Executive Officers and Key Employees
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	103,780
Granted, weighted average grant date fair value (in dollars per share)	$ 76.52	$ 74.23	$ 79.88
Share Based Compensation Arrangement By Share Based Payment Award, Maximum Target Award Percentage	200.00%
Share Based Compensation Arrangement By Share Based Payment Award, Number of Shares to Be Issued at Maximum Performance Target (in shares)	564,862
Time-vested Restricted Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	57,030
Granted, weighted average grant date fair value (in dollars per share)	$ 72
Time-vested Restricted Stock | Executive Officers and Key Employees
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	57,030
Granted, weighted average grant date fair value (in dollars per share)	$ 72	60.68	71.91
Time-vested Restricted Stock | Non Employee Directors
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	15,750
Granted, weighted average grant date fair value (in dollars per share)	$ 71.38	$ 58.03	$ 75.59
Performance-contingent Restricted Stock Unit and Time-vested Restricted Stocks
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation (in shares)	26,892	24,724	18,428
Share-Based Compensation Arrangement by Share-Based Payment Award, Shares Withheld for Tax Withholding Obligations, Weighted Average Price Per Share (in dollars per share)	$ 73.45	$ 60.73	$ 72.03
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 8.0	$ 11.9	$ 8.6
Share Based Compensation Tax Benefit Realized From Exercise Of Equity Instruments Other Than Stock Options	$ 4.0	$ 3.7	$ 3.2