NONCONTROLLING INTERESTS - Operating Partnership Ownership (Details) - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Apr. 18, 2016
May 14, 2015
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Operating Partnership Ownership          
OP Units outstanding which are not owned by the general partner (as a percent)     1.00%   1.10%
OP units issued (in shares) 61,224 20,408      
Issuance of OP Shares $ 1,500 $ 500      
Adjustment for noncontrolling interest in the Operating Partnership     $ 1,756 $ 6,404 $ 7,400
CubeSmart, L.P. and Subsidiaries          
Operating Partnership Ownership          
OP units outstanding (in shares)     1,878,253   2,032,394
Number of trading days used to determine average of the closing prices of the shares     10 days    
Adjustment for noncontrolling interest in the Operating Partnership     $ 1,756 $ 6,404