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Summary of Significant Accounting Policies - Revenue by Geographic Region (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2021
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue $ 139 $ 622 $ 240 $ 934
United States        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue   31 42 373
Europe        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue   $ 591 $ 198 $ 561