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MARKETABLE SECURITIES (Summary of Changes in Fair Value of Company's Marketable Securities) (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]      
Balance at beginning of the period $ 40,966 $ 56,662 $ 56,662
Additions 19,640 2,551 38,702
Sale or maturity (19,852) (23,773) (54,333)
Changes in fair value during the period (76) $ 79 (65)
Balance at end of the period $ 40,678   $ 40,966