Quarterly report pursuant to Section 13 or 15(d)

EARNINGS PER SHARE - Narrative (Details)

v3.20.1
EARNINGS PER SHARE - Narrative (Details)
3 Months Ended
Mar. 31, 2020
shares
Mar. 31, 2019
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  
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) 380,943  
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) 252,894  
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) 51,100,000 54,600,000