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Fair Values of Stock Options Estimated Using Black-Scholes Valuation Model (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Black Scholes Method Used [Line Items]
Expected term (in years)	6 years 14 days	6 years 10 days
Risk-free interest rate	2.67%	2.03%
Dividend yield	0.00%	0.00%
Volatility	92.61%	110.29%
Non Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Black Scholes Method Used [Line Items]
Expected term (in years)		9 years
Risk-free interest rate		2.35%
Dividend yield	0.00%	0.00%
Volatility		111.55%

X

- Definition

Share based compensation arrangement by share based payment award fair value assumptions Black-Scholes method used.

+ References

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The estimated measure of the 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

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

+ References

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-Publisher FASB
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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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