Stock-based Compensation - Fair Value Assumptions (Details)	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Assumptions used in determining fair value of the stock options granted
Expected volatility (minimum)	79.00%	81.00%
Expected volatility (maximum)	80.00%	82.00%
Risk-free interest rate (minimum)	1.46%	2.49%
Risk-free interest rate (maximum)	1.73%	2.56%
Expected dividend yield	0.00%	0.00%
Minimum
Assumptions used in determining fair value of the stock options granted
Expected term (in years)	5 years 10 months 24 days	5 years 6 months 7 days
Maximum
Assumptions used in determining fair value of the stock options granted
Expected term (in years)	6 years 29 days	6 years 7 months 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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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 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
-Publisher FASB
-Name Accounting Standards Codification
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