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Change In Allowances (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Allowances for doubtful accounts      
Balance, beginning of year $ 1,617 $ 645 $ 598
Additions (reversals) charged to expense, net 15 1,164 47
Write-offs (71) (192) 0
Balance, end of year $ 1,561 $ 1,617 $ 645