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Balance Sheet Items - Prepaid Expenses and Other Current Asset (Details) - USD ($)
$ in Thousands
Jun. 30, 2021
Dec. 31, 2020
Prepaid Expense and Other Assets, Current [Abstract]    
Prepaid expenses $ 439 $ 245
Research tax credit 304 0
Prepaid research and development costs 569 441
Notes and interest receivable 38 260
Other current assets 686 59
Total $ 2,036 $ 1,005