CONVERTIBLE PREFERRED STOCK - Schedule of Proceeds from Series D Preferred Stock (Details) - USD ($) $ in Thousands	1 Months Ended					3 Months Ended	9 Months Ended		12 Months Ended	45 Months Ended
	Feb. 28, 2021	Jun. 30, 2020	Mar. 31, 2020	Oct. 31, 2019	Apr. 30, 2019	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2021
Class of Stock [Line Items]
Conversion of preferred stock warrant to Series D in February 2021	$ 3,000					$ 173,300	$ 173,273	$ 0
Series D
Class of Stock [Line Items]
Conversion of Convertible Notes									$ 272,000	$ 271,985
Proceeds from issuance of convertible preferred shares		$ 200,000	$ 200,000	$ 400,000	$ 200,000		$ 3,000	400,000	$ 872,000
Settlement of Series D contingent forward contract liability								$ 39,563		39,564
Conversion of preferred stock warrant to Series D in February 2021										3,000
Reclassification of preferred stock warrant liability to Series D in February 2021	$ 9,936
Total proceeds of Series D										$ 1,324,485