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MARKETABLE SECURITIES - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Cash and Cash Equivalents [Abstract]        
Equity securities, realized gain (loss) $ 4,500 $ 33 $ 1,900 $ (300)