Quarterly report pursuant to Section 13 or 15(d)

Acquisitions, Goodwill and Intangible Assets - Summary of Net Change in Carrying Value of Intangible Assets (Detail)

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Acquisitions, Goodwill and Intangible Assets - Summary of Net Change in Carrying Value of Intangible Assets (Detail) - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Finite-Lived Intangible Assets, Net [Abstract]    
Beginning balance $ 0 $ 0
Additions from acquisition 1,571 0
Amortization (118) 0
Ending balance $ 1,453 $ 0