Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 USD ($) Segment
Summary Of Significant Accounting Policies [Line Items]
Percentage of likelihood of realization required to record tax benefit	50.00%
Contractual obligation	$ 0
Number of reportable segment \| Segment	1
Accounting Standards Update 2014-09 [Member] \| Difference between Revenue Guidance in Effect after Topic 606
Summary Of Significant Accounting Policies [Line Items]
Recognition of additional revenue	$ 5,400,000
Convertible Preferred Stock (Series B, Series A-2, Series A-1, Junior and Founder) [Member]
Summary Of Significant Accounting Policies [Line Items]
Loss to participating securities	$ 0

Percentage of likelihood of realization needed in order for the company to record a tax benefit.

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Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

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Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount of earnings (loss) distributed and earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class method.

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