Quarterly report pursuant to Section 13 or 15(d)

EARNINGS PER SHARE - Narrative (Details)

v3.8.0.1
EARNINGS PER SHARE - Narrative (Details)
 3 Months Ended
Mar. 31, 2018
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Mar. 31, 2017
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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) 345,580  
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)   50,000,000