National Storage Affiliates Trust Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	Jun. 30, 2021 USD ($) partnership property	Dec. 31, 2020 USD ($) property partnership
Variable Interest Entity [Line Items]
Number of self storage properties \| property	864
Net book value of real estate owned	$ 3,572,518	$ 3,195,569
Carrying value of fixed rate mortgages	2,063,541	1,922,614
Fixed rate mortgages payable \| Fixed rate mortgages payable
Variable Interest Entity [Line Items]
Carrying value of fixed rate mortgages	$ 218,041	$ 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	48	34
Net book value of real estate owned	$ 434,000	$ 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