Quarterly report pursuant to Section 13 or 15(d)

EARNINGS PER SHARE - Narrative (Details)

v3.19.3
EARNINGS PER SHARE - Narrative (Details)
 3 Months Ended 9 Months Ended
Sep. 30, 2019
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Sep. 30, 2018
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Sep. 30, 2019
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Sep. 30, 2018
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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  
NSA OP, LP | LTIP units        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Unit conversion ratio     1  
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  
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 units) 448,089   448,089  
LTIP units with vesting based on future acquisitions        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Equity interests excluded from computation of diluted earnings per share (in units) 224,000   224,000  
OP units, DownREIT OP units, Subordinated performance units, DownREIT subordinated performance units, Vested LTIP units        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Equity interests excluded from computation of diluted earnings per share (in units) 55,200,000 51,100,000 53,900,000 50,400,000