FAIR VALUE OF MEASUREMENTS AND INVESTMENT SECURITIES - Fair Value of Warrants (Details)	9 Months Ended	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Derivative [Line Items]
Risk-free interest rate	0.84%	1.18%
Volatility	90.35%	81.78%
Expected life (years)	5 years 7 months 17 days	6 years 10 days
Warrant Derivative Liability
Derivative [Line Items]
Risk-free interest rate	0.95%		0.46%
Volatility	95.00%		90.00%
Expected life (years)	4 years 10 months 20 days		5 years 7 months 20 days
Private Placement Option Liability
Derivative [Line Items]
Risk-free interest rate	1.33%		0.77%
Volatility	95.00%		90.00%
Expected life (years)	7 years		7 years

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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- 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

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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