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Derivatives and Fair Value Measurements - Fair Value of Long-term Debt (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Fair Value of Debt [Line Items]    
Total debt at par value $ 1,547.8 $ 1,310.8
Carrying Amount    
Fair Value of Debt [Line Items]    
Total debt at par value 1,591.3 1,367.2
Less: Unamortized debt issuance costs and original issue discount (43.5) (56.4)
Net carrying amount 1,547.8 1,310.8
Estimated Fair Value    
Fair Value of Debt [Line Items]    
Estimated fair value $ 987.6 $ 1,271.1