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Financial Instruments (Details) - USD ($)
$ in Millions
Mar. 31, 2020
Dec. 31, 2019
Carrying (reported) amount, fair value disclosure [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Long-term debt including current maturities $ 577.3 $ 577.0
Estimate of fair value, fair value disclosure [Member] | Fair value, inputs, level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Long-term debt including current maturities $ 556.7 $ 637.8