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Income Taxes - Changes in Unrecognized Tax Benefits Excluding Interest and Penalties (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Income Tax Disclosure [Abstract]      
Balance at January 1 $ 118 $ 0 $ 0
Additions for tax positions of current year 0 0 0
Additions for tax positions of prior years 0 118 0
Reductions for tax positions of prior years 0 0 0
Expiration of statutes of limitations (52) 0 0
Balance at December 31 $ 66 $ 118 $ 0