EARNINGS PER SHARE - Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator
Net income	$ 17,787	$ 15,763	$ 17,733	$ 12,940	$ 33,550	$ 30,673
Net income attributable to noncontrolling interests	(7,365)		(25,389)		(16,480)	(30,918)
Net income (loss) attributable to National Storage Affiliates Trust	10,422		(7,656)		17,070	(245)
Distributions to preferred shareholders	(3,274)		(3,257)		(6,547)	(5,845)
Distributed and undistributed earnings allocated to participating securities	(11)		(9)		(23)	(18)
Net income (loss) attributable to common shareholders - basic and diluted	$ 7,137		$ (10,922)		$ 10,500	$ (6,108)
Denominator
Weighted average shares outstanding - basic and diluted (in shares)	68,210		57,543		64,004	57,101
Earnings (loss) per share - basic and diluted (in dollars per share)	$ 0.10		$ (0.19)		$ 0.16	$ (0.11)