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Marketable Securities - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2020
Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]      
Marketable securities $ 125,700,000 $ 125,700,000 $ 0
Marketable securities unrealized loss, Less than twelve months 107,900,000 107,900,000  
Marketable securities unrealized loss, more than twelve months 0 0  
Unrealized loss, net 100,000 100,000  
Available-for-sale debt securities remaining maturities greater than two years $ 0 $ 0