MORTGAGE NOTES PAYABLE (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Principal payments on the mortgage notes payable
Total	$ 2,165,027	$ 2,260,836
Mortgage notes
Secured Debt
Weighted average remaining term of notes	5 years
Principal payments on the mortgage notes payable
2013	224,607
2014	106,377
2015	276,400
2016	345,791
2017	276,684
Thereafter	935,168
Total	2,165,027	2,260,836
Long-term debt, other disclosures
Prepayment penalties included in interest expense	2,202	13	190
Deferred financing costs written off	45	72	340
Mortgage notes | Sale of property
Long-term debt, other disclosures
Prepayment penalties included in interest expense	2,115
Deferred financing costs written off	42
Mortgage notes | Deconsolidation of the VIE
Long-term debt, other disclosures
Deferred financing costs written off			216
Mortgage notes | Repayment of mortgages
Long-term debt, other disclosures
Deferred financing costs written off	3	72	124
Fixed rate mortgage notes payable
Secured Debt
Weighted average interest rate (as a percent)	5.30%	5.34%
Principal payments on the mortgage notes payable
Total	1,967,026	2,058,724
Variable rate mortgage notes payable
Secured Debt
Weighted average interest rate (as a percent)	2.77%	2.98%
Principal payments on the mortgage notes payable
Total	$ 198,001	$ 202,112