Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Accumulated amortization	$ (1,613)	$ (1,020)
Intangible assets, net	5,719	6,312
Acquired Technology [Member]
Finite Lived Intangible Assets [Line Items]
Acquired intangible assets	$ 7,252	7,252
Acquired intangible assets, Weighted average remaining useful life	23 months
Acquired Intellectual Property [Member]
Finite Lived Intangible Assets [Line Items]
Acquired intangible assets	$ 80	$ 80