SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Dec. 31, 2024	Nov. 19, 2024	Nov. 14, 2024	Dec. 01, 2023	Jul. 11, 2022
Class of Stock [Line Items]
Preferred shares of beneficial interest, outstanding (in shares)	14,704,845						14,704,845	14,695,458
Authorized amount										$ 350.0	$ 275.0	$ 400.0
Remaining authorized, amount	$ 350.3						$ 350.3
Common Shares
Class of Stock [Line Items]
Redemptions/conversions of units (in shares)	383,901	108,506	93,661	1,048,202	205,910	72,802
Prior Sales Agreement
Class of Stock [Line Items]
Value of common and preferred shares authorized under ATM program									$ 400.0
At The Market Program
Class of Stock [Line Items]
Value of remaining available offered shares	$ 400.0						$ 400.0
Series A Preferred Shares
Class of Stock [Line Items]
Preferred shares of beneficial interest, outstanding (in shares)	9,036,717						9,036,717
NSA OP, LP | Series A-1 preferred units
Class of Stock [Line Items]
Preferred share/unit dividend rate (as a percent)							6.00%
Preferred units cash redemption price (in dollars per share)	$ 25.00						$ 25.00
Unit conversion ratio							1
Minimum conversion period (in years)							10 years
NSA OP, LP | OP units
Class of Stock [Line Items]
Redemptions/conversions of units (in shares)							100,960
Unit conversion ratio							1
Minimum conversion period (in years)							1 year
NSA OP, LP | OP units | Common Shares
Class of Stock [Line Items]
Redemptions/conversions of units (in shares)							586,068
NSA OP, LP | LTIP units
Class of Stock [Line Items]
Unit conversion ratio							1
Conversion of units (in shares)							144,238
Issuance of preferred shares (in shares)							144,238
NSA OP, LP | Class B Unit | Retirement of Northwest
Class of Stock [Line Items]
Issuance of preferred shares (in shares)							199,975
DownREIT Partnership | OP units
Class of Stock [Line Items]
Unit conversion ratio							1
Minimum conversion period (in years)							5 years
Series A Cumulative Redeemable Preferred Shares of Beneficial Interest, par value $0.01 per share
Class of Stock [Line Items]
Preferred share/unit dividend rate (as a percent)							6.00%
Preferred dividends in arrears (in dollars per share)							$ 1.50
Series A Cumulative Redeemable Preferred Shares of Beneficial Interest, par value $0.01 per share | Series A-1 preferred units
Class of Stock [Line Items]
Preferred share/unit dividend rate (as a percent)							6.00%
Series A Cumulative Redeemable Preferred Shares of Beneficial Interest, par value $0.01 per share | NSA OP, LP
Class of Stock [Line Items]
Preferred units cash redemption price (in dollars per share)	$ 25.00						$ 25.00
Series A Cumulative Redeemable Preferred Shares of Beneficial Interest, par value $0.01 per share | NSA OP, LP | Series A Preferred Shares
Class of Stock [Line Items]
Redemptions/conversions of units (in shares)							9,387
Common Shares of Beneficial Interest, $0.01 par value per share | At The Market Program
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)							0