v3.19.1

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) Customers	Dec. 31, 2017 USD ($) Customers	Dec. 31, 2016 USD ($)
Significant Accounting Policies [Line Items]
Restricted cash	$ 300,000	$ 300,000
Impairment loss	0
Advertising expenses	117,300,000	90,500,000
Allowance for doubtful accounts	0	0
Change in cash , cash equivalents and restricted cash	41,884,000	$ 2,613,000	$ 12,650,000
Accounting Standards Update 2016-18 [Member]
Significant Accounting Policies [Line Items]
Change in cash , cash equivalents and restricted cash	$ 300,000
Software [Member]
Significant Accounting Policies [Line Items]
Property plant and equipment useful life	3 years
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Significant Accounting Policies [Line Items]
Cash equivalents	$ 22,700,000
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Significant Accounting Policies [Line Items]
Number of major customers | Customers	2	1
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customers A [Member]
Significant Accounting Policies [Line Items]
Concentration risk percentage	19.00%	20.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customers B [Member]
Significant Accounting Policies [Line Items]
Concentration risk percentage	10.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member]
Significant Accounting Policies [Line Items]
Number of major customers | Customers	2	3
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Customers A [Member]
Significant Accounting Policies [Line Items]
Concentration risk percentage	12.00%	22.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Customers B [Member]
Significant Accounting Policies [Line Items]
Concentration risk percentage	11.00%	12.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Customers C [Member]
Significant Accounting Policies [Line Items]
Concentration risk percentage		11.00%

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Number of major customers representing 10% or more of the Company's accounts receivable.

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Number of major customers representing 10% or more of the Company's revenue.

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Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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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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