Number of largest customers.

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Summary of significant accounting policies line items.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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For a classified balance sheet, the cumulative difference between the rental income or payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, more than one year after the balance sheet date.

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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Present value of lessee's discounted obligation for lease payments from operating lease.

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Amount of lessee's right to use underlying asset under operating lease.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019 USD ($) Segment Customer shares	Mar. 31, 2018 USD ($) Customer shares	Dec. 31, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segment \| Segment	1
Impairment loss of long lived assets	$ 0	$ 0
Number of largest customers \| Customer	3	3
Operating lease asset	$ 16,421,000		$ 0
Operating lease liability	19,470,000
Deferred rent	0		$ 3,001,000
ASU 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease asset	16,700,000
Operating lease liability	19,700,000
Deferred rent	$ 3,000,000
Options to Purchase Common Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Potentially dilutive securities excluded from the calculation of diluted net loss per share \| shares	7,346,935	5,427,390
Customer Concentration Risk [Member] \| Sales Revenue, Net [Member] \| Customer One [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	37.00%	43.00%
Customer Concentration Risk [Member] \| Sales Revenue, Net [Member] \| Customer Two [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	32.00%	38.00%
Customer Concentration Risk [Member] \| Sales Revenue, Net [Member] \| Customer Three [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	26.00%	18.00%
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment useful lives	2 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment useful lives	10 years