Goodwill and Intangible Assets - Schedule of Identifiable Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, Gross Carrying Amount	$ 24,025		$ 23,332
Accumulated Amortization	(7,709)		(6,692)
Intangible assets, net	15,499
Total intangible assets, Net Book Value	16,316	$ 16,640	16,640
Acquired Intangible Assets, Gross Carrying Amount	22,170		22,170
Acquired Intangible Assets, Accumulated Amortization	7,605		6,657
Acquired Intangible Assets, Net Book Value	$ 14,565		15,513
Developed Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted-Average Life	5 years 8 months 12 days
Gross Carrying Amount	$ 20,611		20,611
Accumulated Amortization	(6,664)		(5,756)
Intangible assets, net	$ 13,947		14,855
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted-Average Life	6 years 8 months 12 days
Gross Carrying Amount	$ 1,000		1,000
Accumulated Amortization	(389)		(351)
Intangible assets, net	$ 611		649
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted-Average Life	6 years 1 month 6 days
Gross Carrying Amount	$ 519		519
Accumulated Amortization	(512)		(510)
Intangible assets, net	$ 7		9
Non-compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted-Average Life	2 years
Gross Carrying Amount	$ 40		40
Accumulated Amortization	(40)		(40)
Intangible assets, net	0		0
Internal-use Software [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,855		1,162
Accumulated Amortization	(104)		(35)
Intangible assets, net	$ 1,751		$ 1,127