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Marketable Securities (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Marketable Securities [Abstract]    
Available-for-sale Securities, Gross Realized Gains   $ 5
Available-for-sale Securities, Gross Unrealized Loss   35
Investment Income, Amortization of Premium $ 0 $ 130