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Financial Instruments (Details) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Long-term Debt, Fair Value $ 577.0 $ 576.2
Estimate of fair value of long-term debt, including current maturities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Long-term Debt, Fair Value $ 637.8 $ 577.1