Earnings Per Share ("EPS") of Common Stock - Reconciliation of Numerator and Denominator (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Numerator:
Net income	$ 27.8	$ 18.1
Income allocated to participating securities	(0.1)	(0.1)
Net income for basic EPS	27.7	18.0
Interest on 2¼% Notes	0.7	0.0
Net income for diluted EPS	$ 28.4	$ 18.0
Denominator:
Basic weighted average shares (in shares)	80.2	77.6
Effect of:
2 1/4% Notes (in shares)	5.6	3.1
Diluted weighted average shares (in shares)	85.8	80.7
Basic
Basic earnings per share (in dollars per share)	$ 0.34	$ 0.23
Diluted
Diluted earnings per share (in dollars per share)	$ 0.33	$ 0.22
Convertible Debt | 2 1/4% Notes
Diluted
Debt instrument interest rate stated percentage	2.25%