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Available-for-Sale Debt Securities - Fair Value of Available-For-Sale Debt Securities (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current $ 842.3 $ 781.7
Unrealized gain, current 0.9 0.3
Unrealized loss, current (0.1) (1.5)
Fair value, current 843.1 780.5
Amortized cost, noncurrent 738.8 684.6
Unrealized gain, noncurrent 2.3 3.4
Unrealized loss, noncurrent (1.6) (0.5)
Fair value, noncurrent 739.5 687.5
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 37.1 53.5
Unrealized gain, current 0.0 0.0
Unrealized loss, current 0.0 0.0
Fair value, current 37.1 53.5
Corporate debt securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 527.0 382.1
Unrealized gain, current 0.6 0.1
Unrealized loss, current (0.1) (1.0)
Fair value, current 527.5 381.2
Amortized cost, noncurrent 584.4 483.5
Unrealized gain, noncurrent 2.0 2.9
Unrealized loss, noncurrent (1.0) (0.4)
Fair value, noncurrent 585.4 486.0
Securities of government-sponsored entities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 278.2 346.1
Unrealized gain, current 0.3 0.2
Unrealized loss, current 0.0 (0.5)
Fair value, current 278.5 345.8
Amortized cost, noncurrent 154.4 201.1
Unrealized gain, noncurrent 0.3 0.5
Unrealized loss, noncurrent (0.6) (0.1)
Fair value, noncurrent $ 154.1 $ 201.5