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Long-Term Debt - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Debt Instrument [Line Items]          
Repayments of Long-term Debt $ 0.0 $ 0.0 $ 359.0 $ 350.0  
Line of Credit Facility, Maximum Borrowing Capacity 550.0   550.0    
Gain (Loss) on Extinguishment of Debt 0.0 $ 0.0 11.0 $ 0.0  
Redemption Premium 9.0        
Write off of Deferred Debt Issuance Cost $ 2.0        
Debt Instrument, Redemption Price, Percentage 102.438%        
Payments of Debt Issuance Costs     4.0    
Revolving Credit Facility [Member]          
Debt Instrument [Line Items]          
Long-term debt, gross $ 0.0   $ 0.0   $ 0.0
Revolving Credit Facility [Member] | Minimum [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage 0.20%        
Revolving Credit Facility [Member] | Maximum [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage 0.425%        
Revolving Credit Facility [Member] | Amended Credit Facility [Member]          
Debt Instrument [Line Items]          
Capitalization Ratio, Maximum 57.50%   57.50%    
Revolving Credit Facility [Member] | Amended Credit Facility, A Loan [Member] | Base Rate [Member] | Minimum [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Interest Rate During Period 0.50%        
Revolving Credit Facility [Member] | Amended Credit Facility, A Loan [Member] | Base Rate [Member] | Maximum [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Interest Rate During Period 1.50%        
Revolving Credit Facility [Member] | Amended Credit Facility, A Loan [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Interest Rate During Period 1.50%        
Revolving Credit Facility [Member] | Amended Credit Facility, A Loan [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Interest Rate During Period 2.50%        
Senior Notes [Member] | Senior unsecured notes, maturing 2024 [Member]          
Debt Instrument [Line Items]          
Long-term debt, gross $ 0.0   $ 0.0   350.0
Senior Notes [Member] | Senior unsecured notes, maturing 2029          
Debt Instrument [Line Items]          
Long-term debt, gross $ 350.0   $ 350.0   $ 0.0