MORTGAGE LOANS AND NOTES PAYABLE - Summary (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2025	Dec. 31, 2024
MORTGAGE LOANS AND NOTES PAYABLE
Principal amount of debt	$ 3,250,000	$ 2,800,000
Total mortgage loans and notes payable	204,681	205,915
Net book value of self-storage facilities	6,377,973	6,038,186
Mortgage Loans
MORTGAGE LOANS AND NOTES PAYABLE
Carrying value	203,586
Principal amount of debt	203,586	204,471
Plus: Unamortized fair value adjustment	4,928	6,137
Less: Loan procurement costs, net	(3,833)	(4,693)
Total mortgage loans and notes payable	204,681	205,915
Net book value of self-storage facilities	397,600	403,900
Long Island City II, NY \| Mortgage Loans
MORTGAGE LOANS AND NOTES PAYABLE
Carrying value	$ 17,004	17,368
Effective interest rate (as a percent)	2.25%
Long Island City III, NY \| Mortgage Loans
MORTGAGE LOANS AND NOTES PAYABLE
Carrying value	$ 17,005	17,371
Effective interest rate (as a percent)	2.25%
Allen, TX \| Mortgage Loans
MORTGAGE LOANS AND NOTES PAYABLE
Carrying value	$ 7,277	7,432
Effective interest rate (as a percent)	6.29%
Dallas-Fort Worth, TX \| Mortgage Loans
MORTGAGE LOANS AND NOTES PAYABLE
Carrying value	$ 108,000	108,000
Effective interest rate (as a percent)	6.23%
Flushing II, NY \| Mortgage Loans
MORTGAGE LOANS AND NOTES PAYABLE
Carrying value	$ 54,300	$ 54,300
Effective interest rate (as a percent)	2.15%
Joint Venture
MORTGAGE LOANS AND NOTES PAYABLE
Ownership interest held by the entity (as a percent)	85.00%	85.00%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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