Stock-based Compensation - Fair Value Assumptions (Details)	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Assumptions used in determining fair value of the stock options granted
Expected volatility (minimum)	61.00%	80.00%
Expected volatility (maximum)	82.00%	85.00%
Risk-free interest rate (minimum)	1.44%	2.63%
Risk-free interest rate (maximum)	2.58%	2.96%
Expected dividend yield	0.00%	0.00%
Minimum
Assumptions used in determining fair value of the stock options granted
Expected term (in years)	6 months	5 years 3 months 7 days
Maximum
Assumptions used in determining fair value of the stock options granted
Expected term (in years)	6 years 7 months 17 days	6 years 1 month 17 days

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.

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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.

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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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- Definition

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

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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.

+ References

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