Income Taxes - Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current:
Federal	$ 0.0	$ 0.0	$ 0.0
State	0.0	0.0	0.0
Foreign	7.1	3.0	7.7
Total current	7.1	3.0	7.7
Deferred:
Federal	0.0	0.0	0.0
State	0.0	0.0	0.0
Foreign	0.0	0.0	0.0
Total deferred	0.0	0.0	0.0
Total income tax expense	$ 7.1	$ 3.0	$ 7.7