NET LOSS PER SHARE - POTENTIAL COMMON SHARES EXCLUDED FROM THE CALCULATION OF DILUTED NET INCOME (LOSS) PER SHARE (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	142,376,772	503,485,347	142,376,772	503,485,347
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	112,492,359	65,598,613	112,492,359	65,598,613
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	15,447,206	24,836,871	15,447,206	24,836,871
Unvested shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	65,435	306,966	65,435	306,966
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	14,278,034	0	14,278,034	0
ESPP shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	93,738	0	93,738	0
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	0	412,742,897	0	412,742,897