STOCK BASED COMPENSATION EXPENSE - Stock Option Activity (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares
Options
Outstanding at beginning of period (in shares) | shares	40,012,825
Granted (in shares) | shares	1,582,496
Exercised (in shares) | shares	2,081,577
Cancelled (in shares) | shares	177,504
Options at end of period (in shares) | shares	39,336,240	40,012,825
Vested and exercisable as of period end (in shares) | shares	36,542,071
Weighted Average Exercise Price Per share
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 1.08
Granted (in dollars per share) | $ / shares	5.30
Exercised (in dollars per share) | $ / shares	1.06
Cancelled (in dollars per share) | $ / shares	1.44
Outstanding at end of period (in dollars per share) | $ / shares	1.26	$ 1.08
Vested and exercisable at period end (in dollars per share) | $ / shares	$ 1.20
Weighted Average Remaining Contractual Term (Years)
Outstanding at beginning of period (in years)	8 years 1 month 2 days	8 years 9 months 10 days
Vested and exercisable at period end (in years)	8 years 21 days