MEZZANINE EQUITY, COMMON STOCK AND STOCKHOLDERS' (DEFICIT) EQUITY - SCHEDULE OF SHARE-BASED COMPENSATION (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	$ 1,244,314	$ 1,571	$ 1,254,448	$ 5,348
Brokerage and transaction
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	6,405	6	6,417	18
Technology and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	502,748	992	504,773	3,532
Operations
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	16,410	5	16,416	23
Marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	40,966	40	41,044	55
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	$ 677,785	$ 528	$ 685,798	$ 1,720