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MARKETABLE INVESTMENT SECURITIES - Schedule of Fair Value for Available-for-Sale Securities by Major Security Type and Class of Security (Details) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Cash and cash equivalents:      
Amortized cost $ 132.1 $ 56.9 $ 257.4
Estimated fair value 132.1 56.9  
Total:      
Amortized cost 141.0 172.4  
Gross unrealized holding gains 0.0 0.0  
Gross unrealized holding losses (0.1) (2.7)  
Estimated fair value 140.9 169.7  
Corporate bonds and notes      
Available-for-sale:      
Amortized cost 8.4 66.7  
Gross unrealized holding gains 0.0 0.0  
Gross unrealized holding losses (0.1) (1.6)  
Estimated fair value 8.3 65.1  
Municipal bonds      
Available-for-sale:      
Amortized cost 0.5 16.3  
Gross unrealized holding gains 0.0 0.0  
Gross unrealized holding losses 0.0 (0.3)  
Estimated fair value 0.5 16.0  
Federal agency issues      
Available-for-sale:      
Amortized cost   20.7  
Gross unrealized holding gains   0.0  
Gross unrealized holding losses   (0.7)  
Estimated fair value   20.0  
U.S. government securities      
Available-for-sale:      
Amortized cost   11.8  
Gross unrealized holding gains   0.0  
Gross unrealized holding losses   (0.1)  
Estimated fair value   11.7  
Cash      
Cash and cash equivalents:      
Amortized cost 129.9 53.6  
Estimated fair value 129.9 53.6  
Cash equivalents      
Cash and cash equivalents:      
Amortized cost 2.2 3.3  
Estimated fair value $ 2.2 $ 3.3