Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net unrealized gains (losses)	$ 392.5	$ (30.9)	$ 196.3	$ (195.6)
Securities owned not readily marketable	196.8		196.8		$ 74.3
Level 2 | Measured on a recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 1,485.0		$ 1,485.0		$ 1,528.0