Investment in Unconsolidated Joint Ventures (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets
Commercial real estate property, net	$ 10,010,548	$ 7,973,771
Other assets	737,900	819,443
Liabilities and members' equity
Mortgages and other loans payable	4,314,741	3,400,468
Company's net investment in unconsolidated joint ventures	893,933	631,570
Combined statements of income for the unconsolidated joint ventures
Operating expense	263,709	224,693	209,272
Real estate taxes	174,454	145,830	136,636
Transaction related costs	5,561	11,849
Interest expense, net of interest income	285,917	230,648	232,655
Depreciation and amortization	292,311	240,445	235,200
Total expenses	1,140,848	972,147	1,062,352
Company's equity in net income of unconsolidated joint ventures	1,583	39,607	62,878
Joint venture
Assets
Commercial real estate property, net	5,699,113	4,831,897
Other assets	599,596	516,049
Total assets	6,298,709	5,347,946
Liabilities and members' equity
Mortgages and other loans payable	4,131,890	3,712,235
Other liabilities	250,925	233,463
Members' equity	1,915,894	1,402,248
Total liabilities and equity	6,298,709	5,347,946
Company's net investment in unconsolidated joint ventures	893,933	631,570
Combined statements of income for the unconsolidated joint ventures
Total revenues	480,935	593,159	689,087
Operating expense	75,513	94,515	120,215
Real estate taxes	51,511	66,588	84,827
Transaction related costs	2,665	1,105
Interest expense, net of interest income	223,400	224,766	208,295
Depreciation and amortization	137,070	141,284	156,470
Total expenses	490,159	528,258	569,807
Net (loss) income before gain on sale	(9,224)	64,901	119,280
Company's equity in net income of unconsolidated joint ventures	$ 1,583	$ 39,607	$ 62,878