NONCONTROLLING INTERESTS - Operating Partnership Ownership (Details) - USD ($) $ in Thousands			3 Months Ended						9 Months Ended	12 Months Ended
	Sep. 29, 2020	Dec. 16, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Dec. 31, 2019
Operating Partnership Ownership
OP Units outstanding which are not owned by the general partner (as a percent)			1.10%						1.10%	1.00%
Elimination of noncontrolling interest in subsidiaries due to acquisition						$ 2,618	$ 27,618	$ 10,000
Adjustment for noncontrolling interest in the Operating Partnership			$ (9,312)	$ (615)	$ 7,976	(2,894)	(2,713)	(6,681)	$ (2,000)	$ (5,900)
California
Operating Partnership Ownership
OP units issued (in shares)		106,738
Issuance of OP Shares		$ 3,600
Total consideration		18,500
Cash paid for acquisition		$ 14,900
New York
Operating Partnership Ownership
Total consideration	$ 10,000
Cash paid for acquisition	$ 1,000
Units issued (in shares)	276,497
Units issued	$ 9,000
Cubesmart, L P and Subsidiaries
Operating Partnership Ownership
OP units outstanding (in shares)			2,148,805						2,148,805	1,972,308
Elimination of noncontrolling interest in subsidiaries due to acquisition						2,618	27,618	10,000
Adjustment for noncontrolling interest in the Operating Partnership			$ (9,312)	$ (615)	$ 7,976	$ (2,894)	$ (2,713)	$ (6,681)