SEGMENT REPORTING (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues and net operating income for each of the reportable segments
Total revenues	$ 166,659	$ 164,524	$ 157,649	$ 155,516	$ 148,594	$ 140,030	$ 136,168	$ 136,764	$ 644,348	$ 561,556	$ 498,789
Reconciling items, Revenues									310	155	106
Net operating income, including reconciling items									409,308	344,487	295,368
General and administrative expenses									(34,174)	(29,145)	(25,138)
Interest expense									(125,809)	(127,618)	(120,652)
Depreciation and amortization									(165,642)	(140,713)	(122,772)
Other expenses									(2,741)	(3,225)	(2,871)
Income from continuing operations									80,942	43,786	23,935
Core properties
Revenues and net operating income for each of the reportable segments
Threshold period of time owned									1 year
Apartments owned, Revenues									554,429	530,322	498,683
Net operating income, including reconciling items									351,610	325,194	295,262
Non-core properties
Revenues and net operating income for each of the reportable segments
Apartments owned, Revenues									89,609	31,079
Net operating income, including reconciling items									57,388	19,138
Reconciling items
Revenues and net operating income for each of the reportable segments
Reconciling items, Revenues									$ 310	$ 155	$ 106