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Stock-Based Compensation - Components of Stock-Based Compensation Expense (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Share-based Payment Arrangement [Abstract]    
Equity classified awards expense $ 3.1 $ 4.1
Liability classified awards expense (credit) 1.5 (0.6)
Total pre-tax stock-based compensation expense 4.6 3.5
Book income tax benefit (1.1) (0.9)
Total stock-based compensation expense, net of tax $ 3.5 $ 2.6