STOCK-BASED COMPENSATION - Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
STOCK-BASED COMPENSATION
Options available for grant, beginning of period	11,048	4,299,140	4,299,140
Increase to options available under the plan				5,242,189
Options granted	(18,335)	0	(10,932,615)
Options exercised	(6,465,857)		(996,991)
Options forfeited	18,335		870,317
Options expired			532,017
Options available for grant, end of period	11,048		11,048	4,299,140
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Beginning Balance	51,379,939	42,846,649	42,846,649
Options granted	18,335	0	10,932,615
Options exercised	(6,465,857)		(996,991)
Options forfeited	(18,335)		(870,317)
Options expired			(532,017)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	44,914,082		51,379,939	42,846,649
Weighted average exercise price, options outstanding, beginning of period (per share)	$ 0.58		$ 0.56	$ 0.34
Weighted average exercise price, options granted (per share)	3.47		1.23
Weighted average exercise price, options exercised (per share)	0.43		0.38
Weighted average exercise price, options forfeited (per share)	0.51		0.49
Weighted average exercise price, options expired (per share)			0.35
Weighted average exercise price, options outstanding, end of period (per share)	$ 0.58		$ 0.56	$ 0.34
Weighted average remaining contractual life, options outstanding	7 years 18 days		7 years 2 months 15 days	6 years 9 months 25 days
Aggregate intrinsic value, options outstanding	$ 202,792		$ 46,516	$ 5,821
Weighted average grant date fair value of stock options granted (per share)	$ 2.24		$ 0.82	$ 0.34
Intrinsic value of options exercised	$ 30,200	$ 100	$ 1,100	$ 100

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Number of additional shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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

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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 of the plan that expired.

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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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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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