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

INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURE - Narrative (Details) storage_unit in Thousands, $ in Thousands, ft² in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) ft² storage_unit state property	Sep. 30, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of self storage properties \| property	413
Total rentable square feet in self storage properties owned by the unconsolidated real estate venture \| ft²	25.2
Number of storage units owned by unconsolidated real estate venture \| storage_unit	200
Number of states that unconsolidated real estate venture self storage properties are owned in \| state	25
Contributions to unconsolidated real estate venture \| $	$ 12,647	$ 4,873
Equity Method Investee [Member] \| Real Estate Venture [Member]
Schedule of Equity Method Investments [Line Items]
Number of self storage properties \| property	70
Total rentable square feet in self storage properties owned by the unconsolidated real estate venture \| ft²	4.9
Number of storage units owned by unconsolidated real estate venture \| storage_unit	39
Number of states that unconsolidated real estate venture self storage properties are owned in \| state	13
Number of self storage properties acquired by unconsolidated venture \| property	4
Estimated fair value of self storage properties acquired by unconsolidated real estate venture \| $	$ 49,800
Contributions to unconsolidated real estate venture \| $	$ 12,500
Company's proportionate share of its unconsolidated real estate venture (percent)	25.00%