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Fair Value Measurements - Investments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair Value | $ 2,231.4 | $ 1,940.4
Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of assets on recurring basis | 458.3 | 357.8
Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of assets on recurring basis | 1,773.1 | 1,582.6
Cash and cash equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair Value | 340.2 | 233.0
Cash and cash equivalents | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of assets on recurring basis | 340.2 | 233.0
Cash and cash equivalents | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of assets on recurring basis | 0.0 | 0.0
Available-for-sale debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair Value | 1,773.1 | 1,582.6
Available-for-sale debt securities | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of assets on recurring basis | 0.0 | 0.0
Available-for-sale debt securities | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of assets on recurring basis | 1,773.1 | 1,582.6
Equity investments |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair Value | 118.1 | 124.8
Equity investments | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of assets on recurring basis | 118.1 | 124.8
Equity investments | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of assets on recurring basis | $ 0.0 | $ 0.0

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