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Composition of Certain Financial Statement Captions - Other Current Assets (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Other Current Assets [Abstract] |  |
Prepaid services | $ 131 | $ 277
Prepaid insurance | 639 | 536
Other | 59 | 144
Total other current assets | $ 829 | $ 957

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