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Fair Value Measurements - Schedule of Assets and Liabilities at Fair Value on Recurring Basis (Parenthetical) (Detail) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2019 | Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Contingent consideration, maximum undiscounted payment | $ 4,200 |
Recurring [Member] | Maximum [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Earn-out period for contingent consideration | 7 years |
Recurring [Member] | Minimum [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Earn-out period for contingent consideration | 3 years |
Contingent Consideration [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Beginning balance | $ 2,875 | $ 0
Contingent consideration in connection with acquisitions | 0 | 2,674
Change in fair value of contingent consideration | (11) | 201
Payments of contingent consideration | 0 | 0
Ending balance | $ 2,864 | $ 2,875

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