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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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.

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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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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.

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No definition available.

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

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Stock-Based Compensation - Summary of Assumptions Used in Black-Scholes Option Pricing Model (Detail)			3 Months Ended		9 Months Ended
	Jan. 01, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate			1.62%
Risk-free interest rate, minimum				2.73%	1.62%	2.51%
Risk-free interest rate, maximum				2.99%	2.62%	2.99%
Expected volatility			71.80%
Expected volatility, minimum			71.80%	82.60%	71.80%	82.60%
Expected volatility, maximum				87.60%	75.20%	92.80%
Expected dividend yield			0.00%	0.00%	0.00%	0.00%
Share-based Payment Arrangement, Nonemployee [Member] \| Consultants [Member] \| Re-Measurement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	2.59%	2.06%
Risk-free interest rate, maximum	2.62%	3.02%
Expected volatility, minimum	58.90%	77.40%
Expected volatility, maximum	84.60%	80.90%
Expected dividend yield	0.00%	0.00%
Share-based Payment Arrangement, Nonemployee [Member] \| Consultants [Member] \| Re-Measurement [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)		3 months 4 days
Share-based Payment Arrangement, Nonemployee [Member] \| Consultants [Member] \| Re-Measurement [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)		8 years 5 months 9 days
Employee Options [Member] \| Share-based Payment Arrangement, Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)			6 years 3 months	6 years 3 months	6 years 3 months	6 years 3 months
Employee Options [Member] \| Share-based Payment Arrangement, Nonemployee [Member] \| Consultants [Member] \| Re-Measurement [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)	9 months 22 days
Employee Options [Member] \| Share-based Payment Arrangement, Nonemployee [Member] \| Consultants [Member] \| Re-Measurement [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)	8 years 2 months 9 days