REDEEMABLE PREFERRED STOCK - Issuances, Reclassifications and Redemptions for each class of Preferred Stock in Permanent Equity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		57 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 278,515	$ 278,114	$ 279,539	$ 278,195	$ 278,114	$ 278,195
Reclassification of Series A Preferred Stock from temporary equity to permanent equity					20,724	16,687	$ 121,200
Ending balance	$ 364,526	$ 278,515	$ 284,393	$ 279,539	$ 364,526	$ 284,393	$ 364,526
Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	10,125,641	9,784,067	8,532,056	8,224,254	9,784,067	8,224,254
Beginning balance	$ 270,546	$ 262,036	$ 231,144	$ 223,467	$ 262,036	$ 223,467
Ending balance (in shares)	10,671,562	10,125,641	8,954,508	8,532,056	10,671,562	8,954,508	10,671,562
Ending balance	$ 284,193	$ 270,546	$ 241,667	$ 231,144	$ 284,193	$ 241,667	$ 284,193
Series A Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of Series A Preferred Stock from temporary equity to permanent equity	12,481	8,243	9,739	6,948
Redemption of Series A Preferred Stock	$ (431)	$ (685)	$ (183)	$ (66)
Series A Preferred Stock | Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	4,715,291	4,377,762	3,138,916	2,837,094	4,377,762	2,837,094
Beginning balance	$ 117,140	$ 108,729	$ 78,160	$ 70,633	$ 108,729	$ 70,633
Reclassification of Series A Preferred Stock to permanent equity (in shares)	556,587	366,991	427,064	304,274
Reclassification of Series A Preferred Stock from temporary equity to permanent equity	$ 13,915	$ 9,144	$ 10,638	$ 7,588
Redemption of Series A Preferred Stock (in shares)	(18,501)	(29,462)	(5,532)	(2,452)
Redemption of Series A Preferred Stock	$ (460)	$ (733)	$ (138)	$ (61)
Ending balance (in shares)	5,253,377	4,715,291	3,560,448	3,138,916	5,253,377	3,560,448	5,253,377
Ending balance	$ 130,595	$ 117,140	$ 88,660	$ 78,160	$ 130,595	$ 88,660	$ 130,595
Series D Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Series D Preferred Stock	$ 185	$ 96	$ 22	$ 145
Series D Preferred Stock | Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	23,190	19,145	5,980	0	19,145	0
Beginning balance	$ 572	$ 473	$ 150	$ 0	$ 473	$ 0
Issuance of Series D Preferred Stock (in shares)	7,835	4,045	920	5,980
Issuance of Series D Preferred Stock	$ 192	$ 99	$ 23	$ 150
Ending balance (in shares)	31,025	23,190	6,900	5,980	31,025	6,900	31,025
Ending balance	$ 764	$ 572	$ 173	$ 150	$ 764	$ 173	$ 764
Series L Preferred Stock | Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	5,387,160	5,387,160	5,387,160	5,387,160	5,387,160	5,387,160
Beginning balance	$ 152,834	$ 152,834	$ 152,834	$ 152,834	$ 152,834	$ 152,834
Ending balance (in shares)	5,387,160	5,387,160	5,387,160	5,387,160	5,387,160	5,387,160	5,387,160
Ending balance	$ 152,834	$ 152,834	$ 152,834	$ 152,834	$ 152,834	$ 152,834	$ 152,834