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EARNINGS PER SHARE - Narrative (Details) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 shares | Sep. 30, 2024 shares | Sep. 30, 2025 shares | Sep. 30, 2024 shares
OP units | NSA OP, LP |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Unit conversion ratio |  |  | 1 |
OP units | DownREIT Partnership |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Unit conversion ratio |  |  | 1 |
LTIP units | NSA OP, LP |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Unit conversion ratio |  |  | 1 |
LTIP units with vesting based on service or market condition |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Equity interests excluded from computation of diluted earnings per share (in shares) | 766,017 |  | 766,017 |
OP units, DownREIT OP units, Subordinated performance units, DownREIT subordinated performance units |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Equity interests excluded from computation of diluted earnings per share (in shares) | 57,700,000 | 58,600,000 | 57,900,000 | 58,200,000

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