MEZZANINE EQUITY, COMMON STOCK AND STOCKHOLDERS’ DEFICIT - SCHEDULE OF STOCK OPTION ACTIVITY (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Number of Shares
Beginning balance (in shares)	21,543,828
Exercised during the period (in shares)	(3,581,521)
Cancelled and forfeited during the period (in shares)	(276,657)
Ending balance (in shares)	17,685,650	21,543,828
Options vested and expected to vest (in shares)	17,685,650
Options exercisable (in shares)	15,905,386
Weighted-Average Exercise Price
Beginning balance, Weighted-Average Exercise Price (in dollars per share)	$ 2.19
Exercised during the period, Weighted-Average Exercise Price (in dollars per share)	1.87
Cancelled and forfeited during the period, Weighted-Average Exercise Price (in dollars per share)	4.51
Ending balance, Weighted-Average Exercise Price (in dollars per share)	2.22	$ 2.19
Options vested and expected to vest, Weighted-Average Exercise Price (in dollars per share)	2.22
Options exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 1.75
Weighted- Average Remaining Life
Weighted- Average Remaining Life	5 years 9 months 3 days	6 years 6 months 7 days
Options vested and expected to vest, Weighted-Average Remaining Life	5 years 9 months 3 days
Options exercisable, Weighted-Average Remaining Life	5 years 6 months 21 days
Total Intrinsic Value (in thousands)
Total Intrinsic Value (in thousands)	$ 632,774	$ 304,590
Options vested and expected to vest, Total Intrinsic Value	632,774
Options exercisable, Total Intrinsic Value	$ 576,535