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Marketable Equity Securities (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Marketable Securities [Abstract]    
Marketable equity securities at cost $ 1,879 $ 1,714
Cumulative unrealized (loss) gain on marketable equity securities (840) (129)
Marketable equity securities at fair value $ 1,039 $ 1,585