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Cash, Cash Equivalents and Short-Term Investments - Schedule of Amortized Cost, Unrealized Gains and Losses and Estimated Fair Value of Cash, Cash Equivalents and Short-Term Investments (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Sep. 30, 2024
Cash and Cash Equivalents [Line Items]      
Cash and cash equivalents, amortized cost $ 730.7 $ 1,328.3 $ 517.6
Cash and cash equivalents, estimated fair value 730.7 1,328.3  
Short-term investments, amortized cost 196.3 272.9  
Short-term investments, unrealized gain 0.2 0.2  
Short-term investments, unrealized loss (1.9) (7.2)  
Short-term investments, estimated fair value 194.6 265.9  
Total cash, cash equivalents, and short term investments, before unrealized gains (losses) on investments 927.0 1,601.2  
Total cash, cash equivalents, and short term investments 925.3 1,594.2  
Corporate notes and obligations      
Cash and Cash Equivalents [Line Items]      
Short-term investments, amortized cost 88.5 133.1  
Short-term investments, unrealized gain 0.1 0.2  
Short-term investments, unrealized loss (1.1) (3.3)  
Short-term investments, estimated fair value 87.5 130.0  
U.S. Treasury securities      
Cash and Cash Equivalents [Line Items]      
Short-term investments, amortized cost 80.1 85.0  
Short-term investments, unrealized gain 0.1 0.0  
Short-term investments, unrealized loss (0.6) (2.6)  
Short-term investments, estimated fair value 79.6 82.4  
Municipal securities      
Cash and Cash Equivalents [Line Items]      
Short-term investments, amortized cost 15.4 30.0  
Short-term investments, unrealized gain 0.0 0.0  
Short-term investments, unrealized loss (0.1) (0.7)  
Short-term investments, estimated fair value 15.3 29.3  
Asset backed securities      
Cash and Cash Equivalents [Line Items]      
Short-term investments, amortized cost 6.7 19.2  
Short-term investments, unrealized gain 0.0 0.0  
Short-term investments, unrealized loss (0.1) (0.3)  
Short-term investments, estimated fair value 6.6 18.9  
U.S. agency obligations      
Cash and Cash Equivalents [Line Items]      
Short-term investments, amortized cost 3.8 3.8  
Short-term investments, unrealized gain 0.0 0.0  
Short-term investments, unrealized loss 0.0 (0.2)  
Short-term investments, estimated fair value 3.8 3.6  
Supranational securities      
Cash and Cash Equivalents [Line Items]      
Short-term investments, amortized cost 1.8 1.8  
Short-term investments, unrealized gain 0.0 0.0  
Short-term investments, unrealized loss 0.0 (0.1)  
Short-term investments, estimated fair value 1.8 1.7  
Cash      
Cash and Cash Equivalents [Line Items]      
Cash and cash equivalents, amortized cost 115.3 98.3  
Cash and cash equivalents, estimated fair value 115.3 98.3  
Money market funds      
Cash and Cash Equivalents [Line Items]      
Cash and cash equivalents, amortized cost 615.4 1,230.0  
Cash and cash equivalents, estimated fair value $ 615.4 $ 1,230.0