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

ORGANIZATION AND NATURE OF OPERATIONS (Details) storage_unit in Thousands, ft² in Millions	Sep. 30, 2018 ft² storage_unit property state
Schedule of Equity Method Investments [Line Items]
Number of self storage properties owned \| property	668
Number of states in which self storage properties are owned \| state	34
Total rentable square feet in self storage properties \| ft²	42.5
Number of storage units owned and operated \| storage_unit	341
Consolidated Properties
Schedule of Equity Method Investments [Line Items]
Number of self storage properties owned \| property	492
Number of states in which self storage properties are owned \| state	26
Total rentable square feet in self storage properties \| ft²	30.0
Number of storage units owned and operated \| storage_unit	239
Unconsolidated Properties \| Joint Venture
Schedule of Equity Method Investments [Line Items]
Company's equity interest in Joint Venture (percent)	25.00%
Unconsolidated Properties \| Unconsolidated Real Estate Venture \| Joint Venture
Schedule of Equity Method Investments [Line Items]
Number of self storage properties owned \| property	176
Number of states in which self storage properties are owned \| state	22
Total rentable square feet in self storage properties \| ft²	12.5
Number of storage units owned and operated \| storage_unit	102