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 |