STOCK-BASED COMPENSATION - Stock Options Activity (Details) - Class A common stock - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Number of Options
Outstanding options, beginning balance (in shares)	6,509,591	5,091,005
Granted (in shares)	0	1,880,369
Exercised (in shares)	(2,704,931)	(185,474)
Cancelled (in shares)	(394,273)	(276,309)
Outstanding options, ending balance (in shares)	3,410,387	6,509,591	5,091,005
Exercisable and vested, ending balance (in shares)	3,106,349
Weighted-Average Exercise Price
Outstanding options, beginning balance (USD per share)	$ 4.26	$ 3.94
Granted (USD per share)		5.06
Exercised (USD per share)	4.27	3.58
Cancelled (USD per share)	5.38	2.53
Outstanding options, ending balance (USD per share)	4.13	$ 4.26	$ 3.94
Exercisable and vested, ending balance (USD per share)	$ 4.19
Weighted- Average Remaining Contractual Life (Years)
Outstanding options, weighted average remaining contractual life (years)	4 years 8 months 12 days	6 years 10 months 28 days	8 years 6 months
Exercisable and vested, weighted average remaining contractual life (years)	4 years 4 months 24 days
Aggregate Intrinsic Value
Outstanding, aggregate intrinsic value, beginning balance	$ 118,657	$ 0
Exercised, aggregate intrinsic value	15,706	3,131
Outstanding, aggregate intrinsic value, ending balance	2,496	$ 118,657	$ 0
Exercisable, aggregate intrinsic value	$ 2,123

Share-based Compensation Arrangement by Share-based Payment Award, Options, Intrinsic Value

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Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Weighted Average Remaining Contractual Term

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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