Stock Based Compensation - Schedule of Weighted Average Assumptions Used as Inputs to Black-Scholes Option Pricing Model (Detail) - $ / shares	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted average grant date fair value	$ 9.87	$ 6.90
Expected dividend yield	0.00%	0.00%
Expected stock price volatility	59.00%	66.00%
Risk-free interest rate	2.60%	1.74%
Expected life of options (in years)	6 years 1 month 6 days	6 years 2 months 12 days

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Weighted average expected volatility rate of share-based compensation awards.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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