Quarterly report pursuant to Section 13 or 15(d)

NONCONTROLLING INTERESTS - Equity Interests (Details)

v3.2.0.727
NONCONTROLLING INTERESTS - Equity Interests (Details) - shares
Jun. 30, 2015
Dec. 31, 2014
Partnership Subsidiaries [Member]    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 37,771,815 34,240,410
OP units [Member] | NSA OP, LP [Member]    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 20,705,654 18,817,088
OP units [Member] | DownREIT Partnership [Member]    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 1,415,349 1,275,979
Subordinated performance units [Member] | NSA OP, LP [Member]    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 9,232,067 8,447,679
Subordinated performance units [Member] | DownREIT Partnership [Member]    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 3,688,205 3,009,884
LTIP units [Member] | NSA OP, LP [Member]    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 2,730,540 2,689,780