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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
Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Number Of Shares Available For Grant [Roll Forward]
Options available for grant, beginning of period	11,048	4,299,140	4,299,140
Options granted (in shares)	(18,335)	0	(10,932,615)
Options forfeited (in shares)	18,335		870,317
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 (in shares)	18,335	0	10,932,615
Options exercised (in shares)	(6,465,857)		(996,991)
Options forfeited (in shares)	(18,335)		(870,317)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	44,914,082		51,379,939	42,846,649
Options vested and exercisable (in shares)	32,204,617		37,219,281
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options outstanding, beginning of period, weighted average exercise price (in dollars per share)	$ 0.56	$ 0.34	$ 0.34
Options granted, weighted average exercise price (in dollars per share)	3.47		1.23
Options exercised, weighted average exercise price (in dollars per share)	0.43		0.38
Options forfeited, weighted average exercise price (in dollars per share)	0.51		0.49
Options outstanding, end of period, weighted average exercise price (in dollars per share)	0.58		0.56	$ 0.34
Options vested and exercisable, weighted-average exercise price (in dollars per share)	$ 0.46		$ 0.45
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual life, options outstanding	7 years 18 days		7 years 2 months 15 days	6 years 9 months 25 days
Weighted average remaining contractual life, options vested and exercisable	6 years 3 months 18 days		6 years 5 months 23 days
Aggregate intrinsic value, options outstanding	$ 202,792		$ 46,516	$ 5,821
Aggregate intrinsic value, options vested and exercisable	$ 149,536		$ 37,854

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Share-Based Compensation Arrangement By Share-Based Compensation Award, Options, Number Of Shares Available For Grant

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

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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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 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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