Share-Based Compensation - Compensation Expense for Share-Based Awards (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 11.6	$ 10.1
Income tax benefit	(2.9)	(2.5)
Share-based compensation expense, net of tax benefit	8.7	7.6
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	8.6	8.0
Performance Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 3.0	$ 2.1

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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