Assets Held for Sale and Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Income attributable to discontinued operations
Rental income	$ 4,784	$ 18,613	$ 19,790	$ 39,345
Rental expenses	(2,484)	(3,929)	(5,855)	(10,418)
Depreciation and amortization expense	(1,008)	(5,157)	(4,962)	(9,366)
Other Expenses	(95)	(143)	(160)	(178)
Income attributable to disposed properties and assets	1,197	9,384	8,813	19,383
Net gains on dispositions	9,874	10,834	21,123	14,710
Impairment charges		(2,659)		(2,659)
Income tax on dispositions				(1,916)
Total discontinued operations	$ 11,071	$ 17,559	$ 29,936	$ 29,518