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Marketable Securities - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Marketable Securities [Abstract]        
Interest income, money market deposits $ 2 $ 14 $ 4 $ 127