Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accumulated other comprehensive income(loss)
Amounts reclassified from accumulated other comprehensive income(loss)	$ 0.0	$ 12.8	$ 0.0
Unrealized Gains and Losses on Available-For-Sale Securities
Accumulated other comprehensive income(loss)
Net current-period other comprehensive income		9.9	(20.0)
Foreign Currency Items
Accumulated other comprehensive income(loss)
Net current-period other comprehensive income	$ 4.3	$ (3.5)	$ (4.5)