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Selected Balance Sheet Data - Schedule of Other Assets (Parenthetical) (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Other Assets [Line Items] |  |  |  |  |
Allowance of doubtful accounts | $ 404 |  | $ 404 |  | $ 514
Provision of bad debt expense | 88 | $ 81 | 75 | $ 52 |
Write-off receivables | $ 82 | $ 17 | 185 | 72 |
Reduction of accrued bonuses and other employee related expenses in settlement of employee notes receivable |  |  | $ 60 | $ 192 |
Minimum [Member] |  |  |  |  |
Other Assets [Line Items] |  |  |  |  |
Notes receivable due period |  |  | 1 year |  |
Maximum [Member] |  |  |  |  |
Other Assets [Line Items] |  |  |  |  |
Notes receivable due period |  |  | 5 years |  |

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