Stockholders’ Deficit - Schedule of Fair Value Inputs for Options (Details) - $ / shares	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value per share (in dollars per share)				$ 2.60	$ 1.25
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years		5 years 9 months 14 days	5 years 9 months 14 days
Expected volatility, minimum			63.00%	63.00%	33.00%
Expected volatility, maximum			67.00%	69.00%	35.00%
Dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%
Risk-free interest rate, minimum		0.41%	0.44%	0.40%	1.60%
Risk-free interest rate, maximum		0.61%	1.46%	1.50%	2.60%
Weighted-average grant-date fair value per share (in dollars per share)	$ 6.59
Minimum \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		3 years 11 months 26 days			5 years
Weighted-average grant-date fair value per share (in dollars per share)		$ 4.54	$ 2.56	$ 2.51	$ 1.47
Maximum \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		4 years			6 years 3 months
Weighted-average grant-date fair value per share (in dollars per share)		$ 6.59	$ 2.69	$ 2.77	$ 1.62

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.

+ References

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.

+ References

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.

+ References

No definition available.

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

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No definition available.

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- Definition

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 weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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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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