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Summary of Significant Accounting Policies - Schedule of Disaggregation of Revenue (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disaggregation of Revenue [Line Items]    
Revenues $ 605 $ 2,202
United States    
Disaggregation of Revenue [Line Items]    
Revenues 513 1,997
Europe    
Disaggregation of Revenue [Line Items]    
Revenues $ 92 $ 205