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Marketable Securities - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Marketable Securities [Abstract]        
Interest income, money market deposits $ 5 $ 267 $ 132 $ 299