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Certain Balance Sheet Accounts - Summary of Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Receivables [Abstract]      
Balance, beginning of year $ 155 $ 140 $ 153
Provision for doubtful accounts 567 331 150
Write-offs (363) (316) (163)
Balance, end of year $ 359 $ 155 $ 140