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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
Sep. 30, 2023
Dec. 31, 2022
Sep. 30, 2022
Cash and cash equivalents:      
Amortized cost $ 76.0 $ 56.9 $ 108.7
Estimated fair value 76.0 56.9  
Total      
Amortized cost 86.5 172.4  
Gross unrealized holding gains 0.0 0.0  
Gross unrealized holding losses (0.2) (2.7)  
Estimated fair value 86.3 169.7  
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 (0.2) (1.6)  
Estimated fair value 8.2 65.1  
Municipal bonds      
Available-for-sale:      
Amortized cost 0.6 16.3  
Gross unrealized holding gains 0.0 0.0  
Gross unrealized holding losses 0.0 (0.3)  
Estimated fair value 0.6 16.0  
Federal agency issues      
Available-for-sale:      
Amortized cost 1.5 20.7  
Gross unrealized holding gains 0.0 0.0  
Gross unrealized holding losses 0.0 (0.7)  
Estimated fair value 1.5 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 75.3 53.6  
Estimated fair value 75.3 53.6  
Cash equivalents      
Cash and cash equivalents:      
Amortized cost 0.7 3.3  
Estimated fair value $ 0.7 $ 3.3