Quarterly report pursuant to Section 13 or 15(d)

EARNINGS PER SHARE - Narrative (Details)

v3.10.0.1
EARNINGS PER SHARE - Narrative (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2018
shares
Sep. 30, 2017
shares
Sep. 30, 2018
shares
Sep. 30, 2017
shares
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) 383,712   383,712  
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   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) 51,100,000 51,300,000 50,400,000 50,600,000