Annual report pursuant to Section 13 and 15(d)

EARNINGS PER SHARE - Narrative (Details)

v3.20.4
EARNINGS PER SHARE - Narrative (Details)
12 Months Ended
Dec. 31, 2020
shares
Dec. 31, 2019
shares
Dec. 31, 2018
shares
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) 420,280    
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) 48,200,000 54,200,000 50,600,000
OP units | NSA OP, LP      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio 1    
Minimum conversion period (in years) 1 year    
OP units | DownREIT Partnership      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio 1    
Minimum conversion period (in years) 5 years    
LTIP units | NSA OP, LP      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio 1    
Subordinated performance units | NSA OP, LP      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Minimum conversion period (in years) 2 years    
Subordinated performance units | DownREIT Partnership      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio 1    
Minimum conversion period (in years) 5 years    
Subordinated performance units | NSA OP, LP And DownREIT Partnership      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unit conversion ratio 1    
Minimum conversion period (in years) 2 years