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Investments in Marketable Securities - Gross Realized Gains and Losses from Sale of Available for Sale Securities (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]    
Gross realized gains $ 53 $ 35
Gross realized losses $ 0 $ (47)