Selected Quarterly Financial Information - Schedule of Selected Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 107,944	$ 95,630	$ 96,080	$ 87,635	$ 97,963	$ 82,256	$ 78,016	$ 68,439	$ 387,289	$ 326,674	$ 228,504
Gross profit	76,154	67,248	67,921	62,001	69,512	57,940	53,873	46,368	273,324	227,693	153,071
Loss from operations	(8,603)	(9,237)	(8,201)	(15,702)	(2,172)	(4,418)	(9,938)	(13,051)	(41,743)	(29,579)	(23,081)
Net loss	$ (9,607)	$ (11,265)	$ (10,620)	$ (17,713)	$ (4,311)	$ (6,230)	$ (11,610)	$ (14,507)	$ (49,205)	$ (36,658)	$ (31,778)
Net loss per share, basic and diluted	$ (0.32)	$ (0.37)	$ (0.35)	$ (0.59)	$ (0.15)	$ (0.21)	$ (0.40)	$ (0.50)	$ (1.64)	$ (1.25)	$ (1.12)
Shares used in computing net loss per common share, basic and diluted	30,214,454	30,123,188	30,028,985	29,836,277	29,664,926	29,513,842	29,351,414	29,159,509	30,051,961	29,424,054	28,485,003

The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

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