Quarterly report pursuant to Section 13 or 15(d)

NONCONTROLLING INTERESTS - Equity Interests (Details)

v3.8.0.1
NONCONTROLLING INTERESTS - Equity Interests (Details) - shares
Mar. 31, 2018
Dec. 31, 2017
Partnership Subsidiaries [Member]    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 47,154,655 45,317,526
Series A-1 Preferred Units | NSA OP, LP    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 316,103 0
OP units | NSA OP, LP    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 29,062,706 26,719,607
OP units | DownREIT Partnership    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 1,834,786 1,834,786
Subordinated performance units | NSA OP, LP    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 10,663,892 11,604,738
Subordinated performance units | DownREIT Partnership    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 4,386,999 4,386,999
LTIP units | NSA OP, LP    
Noncontrolling Interest [Line Items]    
Outstanding equity interest (in shares) 890,169 771,396