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Stock-based Compensation Plans (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2021
Sep. 30, 2020
Dec. 14, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 779,150 790,759 578,005    
Weighted-average recognition period, Compensation expense related to stock awards not yet vested 1 year 6 months        
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount $ 9.8        
Number of shares authorized under a Plan         20,500,000
Shares available for future grants under a Plan 4,389,099        
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period 10 years        
Share-based Compensation, Expected Forfeiture Rate 2.00%        
Phantom Share Units (PSUs) [Member]          
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 156,012 162,969 131,182    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period 294,063 203,834 185,808    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value $ 12.09 $ 12.74 $ 11.51 $ 11.16  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instrument Other than Option, Nonvested, Intrinsic Value $ 12.68        
Share-based compensation liability $ 3.1        
Employee Stock [Member]          
Number of shares authorized under a Plan       5,800,000  
Shares available for future grants under a Plan 1,921,631        
Price for shares offered under ESPP, as a percentage of closing price on the first or last day of the offering period 85.00%        
Performance Shares [Member]          
Settlement of performance-based restricted stock units, net of shares withheld for taxes 2 240,412,000,000 103,058,000,000    
Restricted Stock Units (RSUs) [Member]          
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 301,864 251,981 228,121    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period 625,518 223,379 220,795    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value $ 12.88 $ 12.77 $ 11.78 $ 11.41  
Minimum [Member] | Performance Shares [Member]          
Performance Factor 0.00%        
Minimum [Member] | Market-Based Awards          
Performance Factor 0.00%        
Maximum [Member] | Performance Shares [Member]          
Performance Factor 200.00%        
Maximum [Member] | Market-Based Awards          
Performance Factor 200.00%