STOCKHOLDERS' EQUITY - Schedule of Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		64,871,795
Convertible preferred stock, shares issued		64,839,353
Convertible preferred stock, shares outstanding	0	64,839,353	33,668,075
Carrying value	$ 0	$ 200,573	$ 60,770
Convertible preferred stock, liquidation preference		$ 194,727
Common stock issuable upon conversion (in shares)		21,499,770
Series A
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		22,533,945
Convertible preferred stock, shares issued		22,501,503
Convertible preferred stock, shares outstanding		22,501,503
Carrying value		$ 22,357
Convertible preferred stock, liquidation preference		$ 22,502
Common stock issuable upon conversion (in shares)		7,461,168
Series B
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		22,917,726
Convertible preferred stock, shares issued		22,917,726
Convertible preferred stock, shares outstanding		22,917,726
Carrying value		$ 93,479
Convertible preferred stock, liquidation preference		$ 87,225
Common stock issuable upon conversion (in shares)		7,599,178
Series C
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		19,420,124
Convertible preferred stock, shares issued		19,420,124
Convertible preferred stock, shares outstanding		19,420,124
Carrying value		$ 84,737
Convertible preferred stock, liquidation preference		$ 85,000
Common stock issuable upon conversion (in shares)		6,439,424