Stock-Based Compensation - Schedule of Relevant Data Used to Estimate Fair Value of Stock Option Grants (Detail)	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rates, Minimum	1.89%	2.67%	1.89%	2.67%
Risk-free interest rates, Maximum	2.41%	2.93%	2.67%	2.93%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)	6 years	6 years	6 years	6 years
Expected volatility, Minimum	68.60%	69.80%	68.60%	69.80%
Expected volatility, Maximum	68.90%	70.40%	69.50%	71.50%

No definition available.

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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.

+ References

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- Definition

The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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No definition available.

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- Definition

The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

No definition available.

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- Definition

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

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No definition available.

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- Definition

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

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No definition available.

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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