Debt - Settlement of debt (Details) - USD ($) $ in Millions	1 Months Ended				3 Months Ended		9 Months Ended
	Sep. 30, 2023	Aug. 31, 2023	Jun. 30, 2023	May 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Net Loss on Inducements and Settlements					$ 0.0	$ 0.0	$ 12.2	$ 8.3
2015 Senior Convertible Debt | Senior Convertible Debt | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled				$ 5.6
Total Cash Consideration				18.9
Net Loss on Inducements and Settlements				0.4
2017 Senior Convertible Debt | Senior Convertible Debt | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled		$ 18.2		25.9
Total Cash Consideration		42.7		56.3
Net Loss on Inducements and Settlements		$ 3.1		6.6
2017 Junior Convertible Debt | Junior Convertible Debt | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled				6.5
Total Cash Consideration				14.9
Net Loss on Inducements and Settlements				$ 2.1
4.333% 2023 Notes | Senior Indebtedness | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled			$ 1,000.0
Total Cash Consideration			1,000.0
Net Loss on Inducements and Settlements			$ 0.0
2.670% 2023 Notes | Senior Indebtedness | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled	$ 1,000.0
Total Cash Consideration	1,000.0
Net Loss on Inducements and Settlements	$ 0.0