Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

v3.21.1
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ in Thousands
Mar. 31, 2021
USD ($)
partnership
property
Dec. 31, 2020
USD ($)
partnership
property
Variable Interest Entity [Line Items]    
Number of self storage properties | property 844  
Net book value of real estate owned $ 3,334,602 $ 3,195,569
Carrying value of fixed rate mortgages 1,938,049 1,922,614
Fixed rate mortgages payable | Fixed rate mortgages payable    
Variable Interest Entity [Line Items]    
Carrying value of fixed rate mortgages $ 222,549 $ 223,614
VIE, Primary Beneficiary    
Variable Interest Entity [Line Items]    
Number of partnerships considered to be VIEs | partnership 22 21
Number of self storage properties | property 40 34
Net book value of real estate owned $ 268,500 $ 225,100
VIE, Primary Beneficiary | Fixed rate mortgages payable | Fixed rate mortgages payable    
Variable Interest Entity [Line Items]    
Carrying value of fixed rate mortgages $ 100,700 $ 100,700