SELF STORAGE PROPERTIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Real Estate [Abstract]
Land	$ 738,863	$ 649,938
Buildings and improvements	2,892,490	2,435,171
Furniture and equipment	7,839	6,610
Total self storage properties	3,639,192	3,091,719
Less accumulated depreciation	(443,623)	(337,822)
Self storage properties, net	3,195,569	2,753,897
Depreciation expense related to self storage properties	$ 105,900	$ 92,200	$ 76,300