Annual report pursuant to Section 13 and 15(d)

SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details)

v3.6.0.2
SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details)
12 Months Ended
Dec. 16, 2016
USD ($)
$ / shares
shares
Jul. 06, 2016
USD ($)
$ / shares
shares
Apr. 28, 2015
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
unit / shares
$ / shares
shares
Dec. 31, 2015
USD ($)
shares
Dec. 31, 2014
USD ($)
Oct. 11, 2016
USD ($)
agent
Class of Stock [Line Items]              
Proceeds from issuance of common shares | $ $ 105,500,000 $ 237,500,000   $ 378,281,000 $ 278,070,000 $ 0  
Common Shares [Member]              
Class of Stock [Line Items]              
Issuance of shares/units, net of offering costs (in shares)       18,962,209 23,000,000    
Net proceeds from issuance of common shares in IPO | $     $ 278,100,000        
Redemptions of units (in shares)       1,125,503 1,000    
IPO [Member] | Common Shares [Member]              
Class of Stock [Line Items]              
Issuance of shares/units, net of offering costs (in shares)     23,000,000        
Share price (in dollars per share) | $ / shares     $ 13.00        
Over-Allotment Option [Member] | Common Shares [Member]              
Class of Stock [Line Items]              
Issuance of shares/units, net of offering costs (in shares) 675,000 1,571,250 3,000,000        
Follow On Offering [Member] | Common Shares [Member]              
Class of Stock [Line Items]              
Issuance of shares/units, net of offering costs (in shares) 5,175,000 12,046,250          
Share price (in dollars per share) | $ / shares $ 20.48 $ 20.75          
ATM [Member]              
Class of Stock [Line Items]              
Proceeds from issuance of common shares | $       $ 33,600,000      
Number of agents used in ATM program | agent             4
Total value of common shares authorized | $             $ 200,000,000
ATM [Member] | Common Shares [Member]              
Class of Stock [Line Items]              
Issuance of shares/units, net of offering costs (in shares)       1,740,959      
Share price (in dollars per share) | $ / shares       $ 19.54      
LTIP units [Member]              
Class of Stock [Line Items]              
Issuance of shares/units, net of offering costs (in shares)       180,304      
LTIP units forfeited       118,300      
NSA OP, LP [Member] | OP units [Member]              
Class of Stock [Line Items]              
Issuance of shares/units, net of offering costs (in shares)       4,392,081      
Unit conversion ratio | unit / shares       1      
Minimum conversion period       1 year      
Redemptions of units (in shares)       1,125,503      
Number of OP units issued from conversions (in units)       1,302,860      
NSA OP, LP [Member] | Subordinated performance units [Member]              
Class of Stock [Line Items]              
Unit conversion, lock out period       2 years      
NSA OP, LP [Member] | LTIP units [Member]              
Class of Stock [Line Items]              
Unit conversion ratio | unit / shares       1      
Redemptions of units (in shares)       1,302,860      
Number of LTIP units converted (in units)       1,302,860      
DownREIT Partnership [Member] | OP units [Member]              
Class of Stock [Line Items]              
Unit conversion ratio | unit / shares       1      
Minimum conversion period       5 years      
DownREIT Partnership [Member] | Subordinated performance units [Member]              
Class of Stock [Line Items]              
Unit conversion ratio | unit / shares       1      
Minimum conversion period       5 years