Basis of Preparation - Impact on Financial Statements (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Liabilities
Accrued income taxes	$ 17.3	$ 46.5
Current convertible notes	255.5	220.9
Long-term deferred tax liabilities	46.3	60.2
Equity
Additional paid-in capital	753.3	780.8
Retained earnings	$ 851.2	808.4
Cumulative Effect, Period of Adoption, Adjustment
Liabilities
Accrued income taxes		(0.2)
Current convertible notes		34.0
Long-term deferred tax liabilities		(7.6)
Equity
Additional paid-in capital		(36.9)
Retained earnings		10.7
Cumulative Effect, Period of Adoption, Adjusted Balance
Liabilities
Accrued income taxes		46.3
Current convertible notes		254.9
Long-term deferred tax liabilities		52.6
Equity
Additional paid-in capital		743.9
Retained earnings		$ 819.1