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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
Investments, Debt and Equity Securities [Abstract]        
Marketable securities, realized gain $ 22 $ 136 $ 74 $ 426
Marketable securities, realized loss $ 66 $ 8 $ 173 $ 886