Quarterly report pursuant to Section 13 or 15(d)

EARNINGS PER SHARE - Narrative (Details)

v3.2.0.727
EARNINGS PER SHARE - Narrative (Details) - Jun. 30, 2015
shares
unit / shares
shares
NSA OP, LP And DownREIT Partnership [Member] | Subordinated performance units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Minimum conversion period   2 years
Unit conversion ratio   1
NSA OP, LP [Member] | LTIP units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Weighted average outstanding equity interests excluded from computation of earnings (in units) | shares 398,817 398,817
NSA OP, LP [Member] | OP units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Minimum conversion period   1 year
Unit conversion ratio   1
DownREIT Partnership [Member] | OP units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Minimum conversion period   5 years
Unit conversion ratio   1
DownREIT Partnership [Member] | Subordinated performance units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Minimum conversion period   5 years
Participating Regional Operator [Member] | Affiliated Entity [Member] | NSA OP, LP [Member] | LTIP units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Weighted average outstanding equity interests excluded from computation of earnings (in units) | shares 522,900 522,900