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Financial Instruments (Details) - USD ($)
$ in Millions
Sep. 30, 2019
Dec. 31, 2018
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 $ 576.8 $ 576.2
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 $ 631.2 $ 577.1