STOCK-BASED COMPENSATION - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options
Outstanding, beginning balance (in shares)	2,378,474
Granted (in shares)	1,574,543
Exercised (in shares)	(160,509)
Canceled or forfeited (in shares)	(39,764)
Outstanding, ending balance (in shares)	3,752,744	2,378,474
Options vested or expected to vest (in shares)	3,752,744
Options exercisable (in shares)	706,696
Weighted Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 8.03
Granted (in dollars per share)	26.10
Exercised (in dollars per share)	6.85
Cancelled or forfeited (in dollars per share)	4.11
Outstanding, ending balance (in dollars per share)	15.71	$ 8.03
Options vested or expected to vest (in dollars per share)	15.71
Options exercisable (in dollars per share)	$ 7.67
Weighted Average Remaining Life and Intrinsic Value
Options outstanding, remaining life	9 years	9 years 8 months 12 days
Options vested or expected to vest, remaining life	9 years
Options exercisable, remaining life	8 years 7 months 6 days
Options outstanding, intrinsic value	$ 62,842	$ 6,722
Options vested or expected to vest, intrinsic value	62,842
Options exercisable, intrinsic value	$ 17,226