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MARKETABLE SECURITIES - Narrative (Details) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]      
Debt securities, available-for-sale $ 0   $ 0
Permanent impairment loss, debt securities, available for sale 0   0
Proceeds from sale and maturity of marketable securities 1,000,000.0 $ 36,400,000  
Restricted Investments $ 0   $ 0