Quarterly report pursuant to Section 13 or 15(d)

EARNINGS PER SHARE - Narrative (Details)

v3.19.2
EARNINGS PER SHARE - Narrative (Details)
 3 Months Ended 6 Months Ended
Jun. 30, 2019
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Jun. 30, 2018
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Jun. 30, 2019
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NSA OP, LP | OP units      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio     1
Minimum conversion period (in years)     1 year
DownREIT Partnership | OP units      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio     1
Minimum conversion period (in years)     5 years
DownREIT Partnership | Subordinated performance units      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio     1
Minimum conversion period (in years)     5 years
NSA OP, LP And DownREIT Partnership | Subordinated performance units      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio     1
Minimum conversion period (in years)     2 years
Long-Term Incentive Plan Unit based on service or market condition      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Weighted average outstanding equity interests excluded from computation of diluted earnings per share (in units)     448,089
Long-Term Incentive Plan Unit based on future acquisitions      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Weighted average outstanding equity interests excluded from computation of diluted earnings per share (in units)     224,000
OP units, DownREIT OP units, Subordinated performance units, DownREIT subordinated performance units      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Weighted average outstanding equity interests excluded from computation of diluted earnings per share (in units) 54,000,000.0 50,600,000 53,200,000