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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 |  |  |  |  |

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- Definition Amount remaining authorized for purchase of share under share repurchase plan. Includes, but is not limited to, repurchase of stock and unit of ownership. + References No definition available. + Details
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