REDEEMABLE PREFERRED STOCK - Narrative (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Class of Stock [Line Items]
Gross proceeds from issuance of preferred stock and warrants	$ 180,500,000
Net proceeds from issuance of preferred stock	20,899,000	$ 32,912,000
Issuance offering costs for preferred stock and warrants	15,100,000
Non-issuance offering costs for preferred stock and warrants	$ 7,900,000
Series A Preferred Warrants
Class of Stock [Line Items]
Warrants issued (in shares)	4,603,287
Gross proceeds from issuance of preferred stock and warrants	$ 761,000
Issuance offering costs for preferred stock and warrants	142,000
Reclassification to deferred rent receivable and charges	$ 5,000
Warrants outstanding (in shares)	4,603,287
Series A Preferred Stock
Class of Stock [Line Items]
Gross proceeds from issuance of preferred stock and warrants	$ 178,400,000
Issuance offering costs for preferred stock and warrants	14,900,000
Reclassification to deferred rent receivable and charges	$ 1,600,000
Preferred stock, shares outstanding (in shares)	7,369,997
Preferred stock, shares redeemed (in shares)	183,941
Series A Preferred Stock | Preferred Stock, Shares Issued, One
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)	7,166,128
Series A Preferred Stock | Preferred Stock, Shares Issued, Two
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)	387,810
Net proceeds from issuance of preferred stock	$ 0
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)	56,857		19,145
Gross proceeds from issuance of preferred stock and warrants	$ 1,400,000
Net proceeds from issuance of preferred stock		$ 0
Issuance offering costs for preferred stock and warrants	35,000
Reclassification to deferred rent receivable and charges	$ 7,000
Preferred stock, shares outstanding (in shares)	56,857	0	19,145
Preferred stock, shares redeemed (in shares)	0
Series A Preferred Unit
Class of Stock [Line Items]
Number of securities called by warrants or rights (in shares)	1,194,159