Goodwill and Intangible Assets - Schedule of Identifiable Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Accumulated Amortization	$ (6,692)	$ (3,844)
Intangible assets, Net Book Value	15,815
Acquired intangible assets, Gross Carrying Amount	22,170	12,790
Acquired intangible assets, Accumulated Amortization	(6,657)	(3,844)
Acquired intangible assets, Net Book Value	15,513	8,946
Intangible assets, Gross Carrying Amount	23,332	12,790
Intangible assets, net	$ 16,640	8,946
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted- Average Life	6 years 1 month 6 days
Intangible assets, Gross Carrying Amount	$ 519	519
Intangible assets, Accumulated Amortization	(510)	(496)
Intangible assets, Net Book Value	$ 9	23
Developed Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted- Average Life	5 years 8 months 12 days
Intangible assets, Gross Carrying Amount	$ 20,611	11,231
Intangible assets, Accumulated Amortization	(5,756)	(3,118)
Intangible assets, Net Book Value	$ 14,855	8,113
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted- Average Life	6 years 8 months 12 days
Intangible assets, Gross Carrying Amount	$ 1,000	1,000
Intangible assets, Accumulated Amortization	(351)	(197)
Intangible assets, Net Book Value	$ 649	803
Non-compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted- Average Life	2 years
Intangible assets, Gross Carrying Amount	$ 40	40
Intangible assets, Accumulated Amortization	(40)	(33)
Intangible assets, Net Book Value	0	7
Internal-use Software [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Gross Carrying Amount	1,162	0
Intangible assets, Accumulated Amortization	(35)	0
Intangible assets, Net Book Value	$ 1,127	$ 0