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STOCK-BASED COMPENSATION - Narrative (Details) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) shares	May 31, 2021 shares	Dec. 31, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)	9,165,901	9,165,901			11,065,658
Reserved shares of common stock for issuance ( in shares)	30,112,751	30,112,751
Options granted, weighted-average grant date fair value (in dollars per share) | $ / shares		$ 18.92
Options granted (in shares)		1,043,948	2,440,000
Options exercised, intrinsic value | $		$ 63,000	$ 100
Stock option exercises (in shares)	1,440,026	2,842,564
Options exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 1.48	$ 1.72
Shares issued from net settlement (in shares)		839,745
Options converted from net settlement (in shares)		1,426,130
Payments for taxes related to net share settlement of stock options | $		$ 12,622	$ 0
Remaining unrecognized stock-based compensation expense | $	$ 22,800	$ 22,800
Outstanding stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as a percentage of fair value		100.00%
Exercise price as a percentage of fair value for shareholders owning specified minimum amount		110.00%
Significant shareholder threshold used for determining exercise price		10.00%
Exercise period		10 years
Weighted average period for recognition of stock-based compensation expense		3 years 4 months 24 days
Outstanding stock options | Share-based Payment Arrangement, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		25.00%
Vesting period		1 year
Outstanding stock options | Share-based Payment Arrangement, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		2.08%
Vesting period		3 years
RSU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		25.00%
Vesting period		4 years
Right to receive, conversion ratio	1	1
Fair value of grants in period | $		$ 63,700
RSUs vested (in shares)		0
Remaining unrecognized stock-based compensation expense | $	$ 59,600	$ 59,600
Weighted average period for recognition of stock-based compensation expense		5 years 1 month 6 days
2009 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)	8,166,991	8,166,991
2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserved shares of common stock for issuance ( in shares)				23,722,254

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