Annual report pursuant to Section 13 and 15(d)

SUBSEQUENT EVENTS - Subordinated Performance Unit To OP Unit Conversions (Details)

v3.10.0.1
SUBSEQUENT EVENTS - Subordinated Performance Unit To OP Unit Conversions (Details) - shares
 12 Months Ended
Jan. 01, 2019
Dec. 31, 2018
Subordinated performance units [Member]    
Subsequent Event [Line Items]    
Period prior to conversion for conversion rate metric   1 year
Percentage of CAD per unit used in conversion rate calculation   110.00%
Subordinated performance units [Member] | NSA OP, LP [Member]    
Subsequent Event [Line Items]    
Minimum conversion period   2 years
Number of subordinated performance units converted (in units)   929,057
Subordinated performance units [Member] | DownREIT Partnership [Member]    
Subsequent Event [Line Items]    
Minimum conversion period   5 years
Number of subordinated performance units converted (in units)   15,377
OP units [Member] | NSA OP, LP [Member]    
Subsequent Event [Line Items]    
Minimum conversion period   1 year
Issuance of shares/units (in shares)   2,024,170
OP units [Member] | DownREIT Partnership [Member]    
Subsequent Event [Line Items]    
Minimum conversion period   5 years
Subsequent Event [Member] | OP units [Member] | NSA OP, LP [Member]    
Subsequent Event [Line Items]    
Issuance of shares/units (in shares) 876,623  
Subsequent Event [Member] | OP units [Member] | DownREIT Partnership [Member]    
Subsequent Event [Line Items]    
Issuance of shares/units (in shares) 13,475