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Income Taxes - Summary of Valuation Allowance for Deferred Tax Assets (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Deferred Tax Assets, Valuation Allowance [Roll Forward]      
Balance at beginning of year $ 88,433 $ 66,435 $ 44,321
Additions 35,370 21,998 22,114
Deductions 0 0 0
Balance at end of year $ 123,803 $ 88,433 $ 66,435