Stock-Based Compensation - Assumptions Used in Determining Fair Value of Stock Options (Details) - $ / shares	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Stock-Based Compensation
Options to purchase common stock granted to employees and directors	1,356,700	1,215,382
Average risk free interest rate	0.40%	1.00%
Dividend rate	0.00%	0.00%
Expected lives (years)	3 years 7 months 6 days	3 years 10 months 24 days
Expected volatility	94.00%	84.00%
Weighted average exercise price of options granted during the period (per share)	$ 2.68	$ 2.08

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 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

Net number of share options (or share units) granted during the period.

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- Definition

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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No definition available.

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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
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