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Financing Agreements (Schedule of Total Debt) (Details) - USD ($)
3 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Sep. 30, 2020
May 01, 2020
Oct. 07, 2019
Debt Instrument [Line Items]          
Repayments of Long-term Debt $ (12,500,000) $ (12,600,000)      
Long-term Debt, by Current and Noncurrent [Abstract]          
Unsecured debenture interest rate         4.375%
Debt Instrument, Face Amount         $ 425,000,000.0
Revolving credit facility, matures September 2021 222,300,000   $ 222,300,000    
Total Long-term debt 1,643,800,000   $ 1,655,700,000    
Revolving Credit Facility [Member]          
Debt Instrument [Line Items]          
Letters of Credit Outstanding, Amount 9,000,000.0        
Long-term Debt, by Current and Noncurrent [Abstract]          
Line of Credit Facility, Maximum Borrowing Capacity 1,191,000,000.0        
Senior Unsecured 5.00% Notes due on February 14, 2025 [Member]          
Long-term Debt, by Current and Noncurrent [Abstract]          
Unsecured debenture interest rate     5.00%    
Securitization Program [Member]          
Long-term Debt, by Current and Noncurrent [Abstract]          
Revolving credit facility, matures September 2021 82,200,000        
Debt Instrument, Face Amount       $ 110,000,000.0  
Note Securitization Facility [Member]          
Long-term Debt, by Current and Noncurrent [Abstract]          
Revolving credit facility, matures September 2021 $ 90,000,000.0        
Debt Instrument, Face Amount       $ 90,000,000.0