ACQUISITIONS (Details) (USD $)	0 Months Ended	1 Months Ended	12 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended		12 Months Ended
	Sep. 26, 2012 HSRE Venture property	Sep. 30, 2011 HSRE Venture property	Dec. 31, 2012 HSRE Venture m	Sep. 28, 2012 HSRE Venture	Sep. 26, 2011 HSRE Venture	Dec. 31, 2012 2011 Self-storage facilities acquisitions Storage Deluxe assets	Dec. 31, 2012 Self-storage facilities property	Nov. 30, 2011 Self-storage facilities Storage Deluxe Acquisition m property	Dec. 31, 2012 Self-storage facilities Storage Deluxe Acquisition property m facility	Nov. 03, 2011 Self-storage facilities Storage Deluxe Acquisition	Dec. 31, 2012 Self-storage facilities 2012 Self-storage facilities acquisitions property m	Dec. 31, 2012 Self-storage facilities 2011 Self-storage facilities acquisitions	Dec. 31, 2011 Self-storage facilities 2011 Self-storage facilities acquisitions property m
Self-storage facilities
Amount of Storage Deluxe transaction									$ 560,000,000
Number of Self Storage Facilities									22
Number of self-storage facilities acquired (in properties)	9	9					37	16	6		22		11
Aggregate purchase price of acquisition							432,300,000		201,900,000	357,300,000	128,400,000		109,800,000
Intangible value of the in-place leases				8,300,000					12,300,000	18,100,000	13,200,000		7,000,000
Estimated life (in months)			12					12	12		12		12
Amortization expense			2,100,000			15,100,000			7,900,000		4,800,000	4,200,000
Acquisition of remaining interest in real estate ventures (as a percent)				50.00%	50.00%
Number of properties, assumed mortgage									6		2		3
Assumed mortgage debt, at fair value									93,100,000		13,900,000		21,800,000
Outstanding principal balance of mortgage debt assumed on acquisitions									88,900,000		13,400,000		21,400,000
Premium on debt assumed on acquisitions									$ 4,200,000		$ 500,000		$ 400,000