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Income Taxes - Unrecognized Tax Benefits Related to Uncertain Tax Positions (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Income Tax Disclosure [Abstract]      
Balance as of December 31, 2019 $ 20 $ 263 $ 95
Additions related to current period 0 0 208
Additions related to prior periods 0 0 0
Reductions related to prior periods (20) (243) (40)
Balance as of December 31, 2020 $ 0 $ 20 $ 263