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Fair Value Measurements - Fair Value Hierarchy for Financial Assets (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Cash equivalents $ 1,373.2 $ 134.2
Total debt securities, available-for-sale 1,486.4 1,973.3
Convertible notes receivable 10.5 10.5
Other assets 20.5 20.6
Total assets measured at fair value on a recurring basis 2,890.6 2,138.6
U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 648.6 1,150.1
Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 172.2 312.1
Corporate debt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 665.6 511.1
Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Cash equivalents 1,005.3 134.2
Total debt securities, available-for-sale 0.0 0.0
Convertible notes receivable 0.0 0.0
Other assets 20.5 20.6
Total assets measured at fair value on a recurring basis 1,025.8 154.8
Level 1 | U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 0.0 0.0
Level 1 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 0.0 0.0
Level 1 | Corporate debt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 0.0 0.0
Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Cash equivalents 367.9 0.0
Total debt securities, available-for-sale 1,486.4 1,973.3
Convertible notes receivable 0.0 0.0
Other assets 0.0 0.0
Total assets measured at fair value on a recurring basis 1,854.3 1,973.3
Level 2 | U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 648.6 1,150.1
Level 2 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 172.2 312.1
Level 2 | Corporate debt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 665.6 511.1
Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Cash equivalents 0.0 0.0
Total debt securities, available-for-sale 0.0 0.0
Convertible notes receivable 10.5 10.5
Other assets 0.0 0.0
Total assets measured at fair value on a recurring basis 10.5 10.5
Level 3 | U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 0.0 0.0
Level 3 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale 0.0 0.0
Level 3 | Corporate debt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]    
Total debt securities, available-for-sale $ 0.0 $ 0.0