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MORTGAGE LOANS AND NOTES PAYABLE - Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Mortgage loans and Notes payable
Less: Loan procurement costs, net	$ (2,322)	$ (3,275)
Total mortgage loans and notes payable	167,676	216,504
Net book value of self-storage facilities	6,097,670	4,505,814	$ 3,774,485
Mortgage Loans
Mortgage loans and Notes payable
Carrying value	156,385	202,768
Plus: Unamortized fair value adjustment	12,981	15,879
Less: Loan procurement costs, net	(1,690)	(2,143)
Total mortgage loans and notes payable	167,676	216,504
Net book value of self-storage facilities used to secure debt	$ 450,700	539,200
Bronx IX, NY \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value		21,030
Effective interest rate (as a percent)	4.85%
Bronx X, NY \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value		23,148
Effective interest rate (as a percent)	4.64%
Nashville V, TN \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value	$ 2,206	2,261
Effective interest rate (as a percent)	3.85%
New York, NY \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value	$ 29,340	29,981
Effective interest rate (as a percent)	3.51%
Annapolis I, MD \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value	$ 5,099	5,283
Effective interest rate (as a percent)	3.78%
Brooklyn XV, NY \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value	$ 15,423	15,713
Effective interest rate (as a percent)	2.15%
Long Island City IV, NY \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value	$ 12,580	12,852
Effective interest rate (as a percent)	2.15%
Long Island City II, NY \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value	$ 18,714	19,094
Effective interest rate (as a percent)	2.25%
Long Island City III, NY \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value	$ 18,723	19,106
Effective interest rate (as a percent)	2.25%
Flushing II, NY \| Mortgage Loans
Mortgage loans and Notes payable
Carrying value	$ 54,300	$ 54,300
Effective interest rate (as a percent)	2.15%