Investment in Unconsolidated Joint Ventures (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Dec. 31, 2012	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets
Commercial real estate property, net	$ 10,269,630			$ 10,269,630	$ 10,010,548
Other assets	718,326			718,326	737,900
Liabilities and members' equity
Mortgages and other loan payable	4,615,464			4,615,464	4,314,741
Company's net investment in unconsolidated joint ventures	1,032,243			1,032,243	893,933
Combined statements of income for the unconsolidated joint ventures
Operating expenses				298,322	263,709	224,693
Real estate taxes				210,467	174,454	145,830
Transaction related costs				5,625	5,561	11,849
Interest				330,569	285,917	230,648
Depreciation and amortization				332,028	277,345	225,193
Total expenses				1,317,731	1,140,848	972,147
Gain (loss) on early extinguishment of debt	(6,978)	(67)	971	(6,978)	904	(1,900)
Company's equity in net income (loss) of unconsolidated joint ventures				76,418	1,583	39,607
Joint venture
Assets
Commercial real estate property, net	6,910,991			6,910,991	5,699,113
Other assets	728,113			728,113	599,596
Total assets	7,639,104			7,639,104	6,298,709
Liabilities and members' equity
Mortgages and other loan payable	5,358,048			5,358,048	4,131,890
Other liabilities	406,929			406,929	250,925
Members' equity	1,874,127			1,874,127	1,915,894
Total liabilities and members' equity	7,639,104			7,639,104	6,298,709
Company's net investment in unconsolidated joint ventures	1,032,243			1,032,243	893,933
Combined statements of income for the unconsolidated joint ventures
Total revenues				511,157	480,935	593,159
Operating expenses				83,697	75,513	94,515
Real estate taxes				53,613	51,511	66,588
Transaction related costs				2,044	2,665	1,105
Interest				231,215	223,400	224,766
Depreciation and amortization				166,336	137,070	141,284
Total expenses				536,905	490,159	528,258
Gain (loss) on early extinguishment of debt				21,421
Net (loss) income before gain on sale				(4,327)	(9,224)	64,901
Company's equity in net income (loss) of unconsolidated joint ventures				$ 76,418	$ 1,583	$ 39,607