Investment in Unconsolidated Joint Ventures (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets
Commercial real estate property, net	$ 10,269,630	$ 10,010,548
Other assets	718,326	737,900
Liabilities and members' equity
Mortgages and other loans payable	4,615,464	4,314,741
Company's net investment in unconsolidated joint ventures	1,032,243	893,933
Combined statements of income for the unconsolidated joint ventures
Operating expense	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 expense, net of interest income	330,569	285,917	230,648
Depreciation and amortization	351,539	292,311	240,445
Total expenses	1,317,731	1,140,848	972,147
Company's equity in net income of unconsolidated joint ventures	76,418	1,583	39,607
Joint venture
Assets
Commercial real estate property, net	6,910,991	5,699,113
Other assets	728,113	599,596
Total assets	7,639,104	6,298,709
Liabilities and members' equity
Mortgages and other loans payable	5,358,048	4,131,890
Other liabilities	406,929	250,925
Members' equity	1,874,127	1,915,894
Total liabilities and members equity	7,639,104	6,298,709
Company's net investment in unconsolidated joint ventures	1,032,243	893,933
Combined statements of income for the unconsolidated joint ventures
Total revenues	511,157	480,935	593,159
Operating expense	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 expense, net of interest income	231,215	223,400	224,766
Depreciation and amortization	166,336	137,070	141,284
Total expenses	536,905	490,159	528,258
Gain 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 of unconsolidated joint ventures	$ 76,418	$ 1,583	$ 39,607