MORTGAGE LOANS AND NOTES PAYABLE - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Mortgage loans and Notes payable
Less: Loan procurement costs, net	$ (3,382)	$ (4,059)
Total mortgage loans and notes payable	93,707	96,040
Net book value of self-storage facilities	3,833,949	3,774,485
Mortgages
Mortgage loans and Notes payable
Carrying value	92,596	94,494
Plus: Unamortized fair value adjustment	1,303	1,833
Less: Loan procurement costs, net	(192)	(287)
Total mortgage loans and notes payable	93,707	96,040
Net book value of self-storage facilities	202,300	206,300
YSI 26
Mortgage loans and Notes payable
Carrying value	$ 7,635	7,805
Effective interest rate (as a percent)	4.56%
YSI 57
Mortgage loans and Notes payable
Carrying value	$ 2,680	2,740
Effective interest rate (as a percent)	4.61%
YSI 55
Mortgage loans and Notes payable
Carrying value	$ 21,163	21,547
Effective interest rate (as a percent)	4.85%
YSI 24
Mortgage loans and Notes payable
Carrying value	$ 23,378	24,042
Effective interest rate (as a percent)	4.64%
YSI 65
Mortgage loans and Notes payable
Carrying value	$ 2,275	2,313
Effective interest rate (as a percent)	3.85%
YSI 66
Mortgage loans and Notes payable
Carrying value	$ 30,137	30,588
Effective interest rate (as a percent)	3.51%
YSI 68
Mortgage loans and Notes payable
Carrying value	$ 5,328	$ 5,459
Effective interest rate (as a percent)	3.78%

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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