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

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	Sep. 30, 2019 USD ($) partnership property	Dec. 31, 2018 USD ($) partnership property
Variable Interest Entity [Line Items]
Number of self storage properties \| property	735
Net book value of real estate owned	$ 2,741,903	$ 2,391,462
Carrying value of fixed rate mortgages	1,539,323	1,277,638
Mortgages \| Fixed rate mortgages payable
Variable Interest Entity [Line Items]
Carrying value of fixed rate mortgages	$ 264,323	$ 268,138
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	$ 235,100	$ 240,400
VIE, Primary Beneficiary \| Mortgages \| Fixed rate mortgages payable
Variable Interest Entity [Line Items]
Carrying value of fixed rate mortgages	$ 136,900	$ 138,400