Fair Value Measurements and Investments - Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Financial Assets
Cash and cash equivalents	$ 235.2	$ 117.9
Financial Liabilities
Long-term debt	3,160.9	3,129.7
Long-term finance lease obligation	2.5	2.7
Unsecured Debt
Financial Liabilities
Unamortized debt issuance costs	4.6	4.8
Carrying Amount
Financial Assets
Cash and cash equivalents	235.2	117.9
Financial Liabilities
Long-term debt	3,237.2	3,236.5
Estimated Fair Value | Level 1
Financial Assets
Cash and cash equivalents	235.2	117.9
Financial Liabilities
Long-term debt	0.0	0.0
Estimated Fair Value | Level 2
Financial Assets
Cash and cash equivalents	0.0	0.0
Financial Liabilities
Long-term debt	3,160.9	3,129.7
Estimated Fair Value | Level 3
Financial Assets
Cash and cash equivalents	0.0	0.0
Financial Liabilities
Long-term debt	$ 0.0	$ 0.0