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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.

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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

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 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
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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Stock-Based Compensation - Granted to non-employees, prior to the adoption of ASU 2018-07 (Details) - Non-employees - $ / shares		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair value of stock awards granted prior to the adoption of ASU 2018-07
Risk-free interest rate	2.30%	2.07%	2.71%	2.05%
Expected volatility	74.00%	76.90%	74.00%	75.60%
Expected term (in years)	6 years 1 month 6 days	6 years 22 days	6 years 2 months 16 days	6 years 4 months 21 days
ASU 2018-07 \| Minimum
Fair value of stock awards granted prior to the adoption of ASU 2018-07
Risk-free interest rate				2.02%
Expected volatility				74.00%
Expected term (in years)				6 years
Fair value of common stock				$ 0.19
ASU 2018-07 \| Maximum
Fair value of stock awards granted prior to the adoption of ASU 2018-07
Risk-free interest rate				2.31%
Expected volatility				85.00%
Expected term (in years)				10 years
Fair value of common stock				$ 6.28