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Financial Instruments − Fair Value and Concentrations of Credit Risk - Financial Instruments Measured at Fair Value and Related Hierarchy Levels (Details) - USD ($)
$ in Millions
Jun. 30, 2024
Dec. 31, 2023
Investment securities, current:    
Debt securities, current $ 3,322.5 $ 3,022.1
Investment securities, non-current:    
Fair value 65.7 66.8
Executive deferred compensation plan trust 15.6 13.7
Prepaid expenses and other current assets    
Investment securities, non-current:    
Executive deferred compensation plan trust 1.4 1.7
Other assets    
Investment securities, non-current:    
Executive deferred compensation plan trust 14.2 12.0
Accrued expenses and other current liabilities    
Liabilities    
Contingent consideration 64.8 64.5
Other liabilities    
Liabilities    
Contingent consideration 60.3 121.7
Debt securities    
Investment securities, non-current:    
Debt securities 27.4 28.4
Municipal bonds    
Investment securities, current:    
Debt securities, current 65.4 65.7
Asset-backed securities    
Investment securities, current:    
Debt securities, current 671.2 581.6
Mortgage-backed securities    
Investment securities, current:    
Debt securities, current 993.2 927.4
Mutual fund    
Investment securities, non-current:    
Equity securities, FV-NI, noncurrent 25.4 25.5
Pooled investment fund measured at NAV    
Investment securities, non-current:    
Equity securities, FV-NI, noncurrent 12.9 12.9
Level 1    
Investment securities, non-current:    
Executive deferred compensation plan trust 15.6 13.7
Level 1 | Money market funds    
Assets:    
Money market funds 44.1 25.5
Level 1 | Mutual fund    
Investment securities, non-current:    
Equity securities, FV-NI, noncurrent 25.4 25.5
Level 2 | US Treasury Bill Securities    
Assets:    
Money market funds 0.0 10.4
Level 2 | Debt securities    
Investment securities, non-current:    
Debt securities 27.4 28.4
Level 2 | U.S. treasury notes    
Investment securities, current:    
Debt securities, current 395.1 378.6
Level 2 | Corporate debt securities    
Investment securities, current:    
Debt securities, current 1,197.6 1,068.8
Level 2 | Municipal bonds    
Investment securities, current:    
Debt securities, current 65.4 65.7
Level 2 | Asset-backed securities    
Investment securities, current:    
Debt securities, current 671.2 581.6
Level 2 | Mortgage-backed securities    
Investment securities, current:    
Debt securities, current 993.2 927.4
Net Asset Value | Pooled investment fund measured at NAV    
Investment securities, non-current:    
Equity securities, FV-NI, noncurrent 12.9 12.9
Level 3 | Contingent consideration    
Liabilities    
Contingent consideration $ 125.1 $ 186.2