Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated other comprehensive income(loss)
Amounts reclassified from accumulated other comprehensive income(loss)	$ 12.8	$ 0.0	$ 0.0
Gains and Losses on Available-For-Sale Securities
Accumulated other comprehensive income(loss)
Net current-period other comprehensive income	9.9	20.0	2.7
Foreign Currency Items
Accumulated other comprehensive income(loss)
Net current-period other comprehensive income	$ 3.5	$ 4.5	$ 1.3