Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated other comprehensive income(loss)
Amounts reclassified from accumulated other comprehensive income(loss)	$ 10.8	$ 0.0	$ 10.8	$ 0.0
Gains and Losses on Available-For-Sale Securities
Accumulated other comprehensive income(loss)
Net current-period other comprehensive income	4.3	5.0	11.8	23.4
Foreign Currency Items
Accumulated other comprehensive income(loss)
Net current-period other comprehensive income	$ 3.0	$ 1.0	$ 1.7	$ 10.1