Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Summary of Net Property Operations Income by Segment
Property rentals	$ 158,153		$ 147,364		$ 468,024		$ 443,119
Straight-line rents	3,082		3,815		10,090		11,846
Total rental income	161,235		151,179		478,114		454,965
Tenant recovery income	26,189		22,461		76,375		67,904
Other property income	4,114		4,499		11,968		13,836
Lodging income	181,836		134,336		514,118		387,885
Total income	373,374		312,475		1,080,575		924,590
Operating expenses	177,675		139,815		505,174		408,338
Net property operations	195,699		172,660		575,401		516,252
Non allocated expenses	(128,169)	[1]	(121,395)	[1]	(380,304)	[1]	(358,443)	[1]
Other income and expenses	(74,807)	[2]	(69,856)	[2]	(221,672)	[2]	(199,854)	[3]
Equity in loss/earnings of unconsolidated affiliates	(1,265)	[4]	2,972		(2,949)	[4]	8,408
Provision for asset impairment	(39,002)		(6,031)		(63,520)		(21,165)
Net loss from continuing operations	(47,544)		(21,650)		(93,044)		(54,802)
Net loss from discontinued operations	34,627		(27,302)		32,124		(72,667)
Net loss	(12,917)		(48,952)		(60,920)		(127,469)
Less: Net income attributable to noncontrolling interests	(4,659)		(2,725)		(4,851)		(6,596)
Net loss attributable to Company	(17,576)		(51,677)		(65,771)		(134,065)
Real estate assets, net	9,257,948				9,257,948
Non-segmented assets	1,578,475				1,578,475
Total assets	10,836,423				10,836,423				10,919,190
Capital Expenditures					59,546
Retail [Member]
Summary of Net Property Operations Income by Segment
Property rentals	78,431		72,511		233,547		217,418
Straight-line rents	(1,243)		(1,757)		(5,159)		(5,244)
Tenant recovery income	18,353		16,502		53,163		48,293
Other property income	989		1,029		2,984		3,816
Lodging income	0		0		0		0
Total income	99,016		91,799		294,853		274,771
Operating expenses	26,131		24,436		77,406		74,858
Net property operations	72,885		67,363		217,447		199,913
Real estate assets, net	3,589,113				3,589,113
Capital Expenditures					13,318
Industrial [Member]
Summary of Net Property Operations Income by Segment
Property rentals	20,865		19,692		62,618		59,634
Straight-line rents	(556)		(1,081)		(1,747)		(3,235)
Tenant recovery income	689		481		2,790		1,717
Other property income	15		527		339		907
Lodging income	0		0		0		0
Total income	22,125		21,781		67,494		65,493
Operating expenses	1,665		1,645		6,411		5,498
Net property operations	20,460		20,136		61,083		59,995
Real estate assets, net	834,194				834,194
Capital Expenditures					2,349
Office [Member]
Summary of Net Property Operations Income by Segment
Property rentals	36,067		35,301		107,598		107,630
Straight-line rents	(1,246)		(954)		(2,988)		(3,247)
Tenant recovery income	7,040		5,364		20,067		17,545
Other property income	793		1,256		2,486		4,050
Lodging income	0		0		0		0
Total income	45,146		42,875		133,139		132,472
Operating expenses	11,205		10,018		32,576		32,321
Net property operations	33,941		32,857		100,563		100,151
Real estate assets, net	1,515,957				1,515,957
Capital Expenditures					4,099
Lodging [Member]
Summary of Net Property Operations Income by Segment
Property rentals	0		0		0		0
Straight-line rents	0		0		0		0
Tenant recovery income	0		0		0		0
Other property income	0		0		0		0
Lodging income	181,836		134,336		514,118		387,885
Total income	181,836		134,336		514,118		387,885
Operating expenses	126,963		92,696		355,763		264,397
Net property operations	54,873		41,640		158,355		123,488
Real estate assets, net	2,610,567				2,610,567
Capital Expenditures					38,093
Multi-Family [Member]
Summary of Net Property Operations Income by Segment
Property rentals	22,790		19,860		64,261		58,437
Straight-line rents	(37)		(23)		(196)		(120)
Tenant recovery income	107		114		355		349
Other property income	2,317		1,687		6,159		5,063
Lodging income	0		0		0		0
Total income	25,251		21,684		70,971		63,969
Operating expenses	11,711		11,020		33,018		31,264
Net property operations	13,540		10,664		37,953		32,705
Real estate assets, net	708,117				708,117
Capital Expenditures					$ 1,687

[1] Non allocated expenses consist of general and administrative expenses, Business Manager management fee and depreciation and amortization.

[2] Other income and expenses consist of interest and dividend income, interest expense, other income, realized gain (loss) on securities, net, and income tax expense.

[3] ther income and expenses consist of interest and dividend income, interest expense, other income and expenses, realized gain on securities, and income tax benefit.

[4] Equity in loss of unconsolidated entities includes the impairment/loss of investment in unconsolidated entities.