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Financial Instruments Investments in Marketable Debt Securities - Additional Information (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
Security
Dec. 31, 2019
USD ($)
Maximum    
Schedule Of Available For Sale Securities [Line Items]    
Available-for-sale securities, period of unrealized loss positions 12 months 12 months
Minimum    
Schedule Of Available For Sale Securities [Line Items]    
Available-for-sale securities, period of unrealized loss positions 12 months 12 months
Debt Securities    
Schedule Of Available For Sale Securities [Line Items]    
Number of available-for-sale securities in unrealized loss positions | Security 34  
Interest and Investment Income Net    
Schedule Of Available For Sale Securities [Line Items]    
Available for sale equity securities,Net unrealized gains $ 3.0 $ 0.3
Marketable Securities.    
Schedule Of Available For Sale Securities [Line Items]    
Equity securities with readily eterminable fair value,Amount $ 6.3 $ 3.4