Long-Term Debt - Interest Expense Components for the 2¼% Notes (Details) - 2 1/4% Notes - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Debt Instrument [Line Items]
Interest expense-contractual interest	$ 0.8	$ 0.8
Interest expense-amortization of debt discount (see discussion above)	0.0	1.1
Interest expense-amortization of deferred financing costs	$ 0.1	$ 0.1