Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ in Thousands
Mar. 31, 2023
USD ($)
property
partnership
Dec. 31, 2022
USD ($)
Variable Interest Entity [Line Items]    
Number of self storage properties | property 1,117  
Net book value of real estate owned $ 5,731,956 $ 5,618,911
Carrying value of fixed rate mortgages 3,653,928 3,560,570
Fixed rate mortgages payable | Fixed rate mortgages payable    
Variable Interest Entity [Line Items]    
Carrying value of fixed rate mortgages $ 298,428 299,570
VIE, Primary Beneficiary    
Variable Interest Entity [Line Items]    
Number of partnerships considered to be VIEs | partnership 22  
Number of self storage properties | property 48  
Net book value of real estate owned $ 412,000 412,900
VIE, Primary Beneficiary | Fixed rate mortgages payable | Fixed rate mortgages payable    
Variable Interest Entity [Line Items]    
Carrying value of fixed rate mortgages $ 188,700 $ 188,700