Segment Reporting (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	Dec. 31, 2011
Summary of Net Property Operations Income by Segment
Property rentals	$ 161,558	$ 152,397	$ 320,040	$ 304,464
Straight-line rents	1,382	3,577	5,445	6,980
Amortization of acquired above and below market leases, net	944	316	1,315	1,094
Total rental income	163,884	156,290	326,800	312,538
Tenant recovery income	26,344	22,494	50,330	45,633
Other property income	4,265	5,063	8,490	9,844
Lodging income	206,791	149,267	356,867	276,922
Total income	401,284	333,114	742,487	644,937
Operating expenses	191,608	146,787	348,207	288,366
Net property operations	209,676	186,327	394,280	356,571
Non allocated expenses	(130,515)	(123,068)	(257,667)	(244,796)
Other income and expenses	(78,698)	(68,510)	(151,541)	(134,315)
Equity in loss/earnings of unconsolidated affiliates	2,936	7,733	(1,683)	5,435
Provision for asset impairment	(17,458)	(10,821)	(27,887)	(17,314)
Net loss from continuing operations	(14,059)	(8,339)	(44,498)	(34,419)
Net loss from discontinued operations	(3,732)	(17,775)	(3,503)	(44,099)
Net loss	(17,791)	(26,114)	(48,001)	(78,518)
Less: Net income attributable to noncontrolling interests	(119)	(1,647)	(192)	(3,871)
Net loss attributable to Company	(17,910)	(27,761)	(48,193)	(82,389)
Real estate assets, net	9,542,434		9,542,434
Non-segmented assets	1,526,790		1,526,790
Total Assets	11,069,224		11,069,224		10,919,190
Capital Expenditures			39,736
Office [Member]
Summary of Net Property Operations Income by Segment
Property rentals	36,298	35,811	71,588	72,351
Straight-line rents	311	1,065	1,595	2,380
Amortization of acquired above and below market leases, net	57	(32)	90	(109)
Total rental income	36,666	36,844	73,273	74,622
Tenant recovery income	6,538	5,842	13,028	12,182
Other property income	760	1,736	1,693	2,794
Lodging income	0	0	0	0
Total income	43,964	44,422	87,994	89,598
Operating expenses	10,471	10,796	21,370	22,304
Net property operations	33,493	33,626	66,624	67,294
Real estate assets, net	1,532,938		1,532,938
Capital Expenditures			2,873
Retail [Member]
Summary of Net Property Operations Income by Segment
Property rentals	79,559	73,982	158,024	147,080
Straight-line rents	652	1,130	2,433	2,147
Amortization of acquired above and below market leases, net	887	415	1,292	1,339
Total rental income	81,098	75,527	161,749	150,566
Tenant recovery income	18,185	15,844	34,949	31,981
Other property income	1,636	1,092	2,493	2,788
Lodging income	0	0	0	0
Total income	100,919	92,463	199,191	185,335
Operating expenses	27,465	24,681	51,991	50,728
Net property operations	73,454	67,782	147,200	134,607
Real estate assets, net	3,699,040		3,699,040
Capital Expenditures			9,154
Industrial [Member]
Summary of Net Property Operations Income by Segment
Property rentals	20,928	19,869	41,761	39,875
Straight-line rents	569	1,339	1,258	2,357
Amortization of acquired above and below market leases, net	0	(67)	(67)	(136)
Total rental income	21,497	21,141	42,952	42,096
Tenant recovery income	1,458	690	2,105	1,235
Other property income	(169)	357	323	380
Lodging income	0	0	0	0
Total income	22,786	22,188	45,380	43,711
Operating expenses	2,829	1,922	4,760	3,863
Net property operations	19,957	20,266	40,620	39,848
Real estate assets, net	843,058		843,058
Capital Expenditures			2,339
Lodging [Member]
Summary of Net Property Operations Income by Segment
Property rentals	0	0	0	0
Straight-line rents	0	0	0	0
Amortization of acquired above and below market leases, net	0	0	0	0
Total rental income	0	0	0	0
Tenant recovery income	0	0	0	0
Other property income	0	0	0	0
Lodging income	206,791	149,267	356,867	276,922
Total income	206,791	149,267	356,867	276,922
Operating expenses	138,616	97,485	245,619	187,734
Net property operations	68,175	51,782	111,248	89,188
Real estate assets, net	2,718,939		2,718,939
Capital Expenditures			24,292
Multi-Family [Member]
Summary of Net Property Operations Income by Segment
Property rentals	24,773	22,735	48,667	45,158
Straight-line rents	(150)	43	159	96
Amortization of acquired above and below market leases, net	0	0	0	0
Total rental income	24,623	22,778	48,826	45,254
Tenant recovery income	163	118	248	235
Other property income	2,038	1,878	3,981	3,882
Lodging income	0	0	0	0
Total income	26,824	24,774	53,055	49,371
Operating expenses	12,227	11,903	24,467	23,737
Net property operations	14,597	12,871	28,588	25,634
Real estate assets, net	748,459		748,459
Capital Expenditures			$ 1,078