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Marketable Securities (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Marketable Securities [Abstract]        
Available-for-sale Securities, Gross Realized Gains   $ 5   $ 5
Investment Income, Amortization of Premium $ 0 $ 88 $ 0 $ 218