Goodwill and Acquired Intangible Assets - Summary of Acquired Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful life (years)	5 years 8 months 12 days	6 years
Gross Carrying Amount	$ 4,513	$ 4,513
Accumulated Amortization	(1,461)	(1,329)
Net Book Value	$ 3,052	$ 3,184
Acquired Technology [Member]
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful life (years)	5 years 9 months 18 days	6 years
Gross Carrying Amount	$ 3,753	$ 3,753
Accumulated Amortization	(1,321)	(1,216)
Net Book Value	$ 2,432	$ 2,537
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful life (years)	5 years 8 months 12 days	6 years
Gross Carrying Amount	$ 480	$ 480
Accumulated Amortization	(90)	(71)
Net Book Value	$ 390	$ 409
Trade Name and Other [Member]
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful life (years)	5 years 8 months 12 days	6 years
Gross Carrying Amount	$ 280	$ 280
Accumulated Amortization	(50)	(42)
Net Book Value	$ 230	$ 238