BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred Rent Receivable and Charges (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Deferred rent receivable	$ 20,858	$ 20,470
Deferred leasing costs, net of accumulated amortization of $8,687 and $7,742, respectively	8,108	8,950
Deferred leasing costs, accumulated amortization	8,687	7,742
Deferred offering costs	6,296	6,046
Other deferred costs	492	490
Deferred rent receivable and charges, net	$ 35,754	$ 35,956