Property Transactions (Components of Income (Loss) from Discontinued Operations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components of Income (Loss) from Discontinued Operations
Impairment losses	$ (14,278)	$ (107,763)	$ (2,554)
Income (loss) from discontinued operations	(1,201)	1,390	12,853
Discontinued Operations [Member]
Components of Income (Loss) from Discontinued Operations
Rental property revenues	22,517	41,092	46,613
Third party management and leasing revenues	16,364	19,359	18,976
Other income	3,526	179	4,814
Rental property expenses	(6,746)	(15,480)	(16,824)
Third party management and leasing expenses	(13,679)	(16,584)	(17,393)
Depreciation and amortization	(9,344)	(19,481)	(23,268)
Impairment losses	(13,790)	(7,632)	0
Other	(49)	(63)	(65)
Income (loss) from discontinued operations	$ (1,201)	$ 1,390	$ 12,853