Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 property	Sep. 30, 2011	Dec. 31, 2011 property
Discontinued Operations
Number of properties whose ownership is transferred by the entity			1		3
Number of properties sold			3		6
Results of operations reclassified as discontinued operations
Rental revenue	$ 3,745	$ 9,587	$ 15,647	$ 31,277
Expenses
Property operating expenses	1,016	3,494	3,900	11,907
Interest expense	1,006	3,748	4,179	15,699
Real estate taxes	544	1,805	2,131	6,119
Asset impairment losses		40,721	599	41,192	38,800
Property and asset management fees	112	702	896	2,371
Depreciation and amortization	1,686	4,124	5,869	14,433
Total expenses	4,364	54,594	17,574	91,721
Benefit (provision) for income taxes		431	(5)
Gain on troubled debt restructuring		1,441	3,386	3,582
Interest and other income (expense)	7	(4)	228	(8)
Income (loss) from discontinued operations	$ (612)	$ (43,139)	$ 1,682	$ (56,870)