National Storage Affiliates Trust Annual report pursuant to Section 13 and 15(d)

ORGANIZATION AND NATURE OF OPERATIONS - Narrative (Details) storage_unit in Thousands, ft² in Millions	12 Months Ended
	Dec. 31, 2019 ft² metropolitan_statistical_area property state storage_unit
Real Estate Properties [Line Items]
Number of top metropolitan statistical areas for focus of operations \| metropolitan_statistical_area	100
Number of self storage properties	742
Number of states in which self storage properties are located \| state	35
Total rentable square feet in self storage properties \| ft²	47.1
Number of storage units	378,000
Consolidated properties
Real Estate Properties [Line Items]
Number of self storage properties	567
Number of states in which self storage properties are located \| state	29
Total rentable square feet in self storage properties \| ft²	34.5
Number of storage units \| storage_unit	275
Unconsolidated properties \| Joint Venture
Real Estate Properties [Line Items]
Number of self storage properties	175
Number of states in which self storage properties are located \| state	21
Total rentable square feet in self storage properties \| ft²	12.6
Number of storage units	103,000
Company's equity interest in unconsolidated real estate ventures (percent)	25.00%