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Retirement Plans - Defined Benefit Retirement Plans - Narrative (Details)
$ in Millions
 12 Months Ended
Sep. 30, 2024
USD ($)
participant
Sep. 30, 2023
USD ($)
Sep. 30, 2022
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost (benefit) $ 0.1 $ 0.3 $ (0.1)
Expected long-term return (as a percent) 4.65%    
Defined benefit plan contributions $ 0.1 0.1  
Defined benefit plan, expected future benefit payment, year one 2.0    
Defined benefit plan, expected future benefit payment, year two 2.0    
Defined benefit plan, expected future benefit payment, year three 2.0    
Defined benefit plan, expected future benefit payment, year four 2.1    
Defined benefit plan, expected future benefit payment, year five 2.1    
Defined benefit plan, expected future benefit payment, five fiscal years thereafter 9.4    
Qualified Plan      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, amount 32.3 29.6  
Defined benefit plan, benefit obligation $ 25.9 $ 24.6  
Defined benefit plan, assumptions used calculating benefit obligation, discount rate (as a percent) 4.90% 5.80%  
Defined benefit plan, funded (unfunded) status of plan $ 6.4 $ 5.0  
Nonqualified Plan      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, benefit obligation 1.1 1.1  
Defined benefit plan, funded (unfunded) status of plan $ (1.1) (1.1)  
Defined contribution plan, number of active participants | participant 0    
Nonqualified Plan | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, amount $ 0.1 $ 0.1  
Debt Securities      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, actual allocation, percentage (as a percent) 90.00%    
Equity Securities      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, actual allocation, percentage (as a percent) 10.00%