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

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	Jun. 30, 2020 USD ($) partnership property	Dec. 31, 2019 USD ($) partnership property
Variable Interest Entity [Line Items]
Number of self storage properties \| property	784
Net book value of real estate owned	$ 2,964,626	$ 2,753,897
Carrying value of fixed rate mortgages	1,746,349	1,539,260
Mortgages \| Fixed rate mortgages payable
Variable Interest Entity [Line Items]
Carrying value of fixed rate mortgages	$ 260,349	$ 264,260
VIE, Primary Beneficiary
Variable Interest Entity [Line Items]
Number of partnerships considered to be VIEs \| partnership	21	21
Number of self storage properties \| property	34	34
Net book value of real estate owned	$ 229,200	$ 233,100
VIE, Primary Beneficiary \| Mortgages \| Fixed rate mortgages payable
Variable Interest Entity [Line Items]
Carrying value of fixed rate mortgages	$ 135,400	$ 136,400