Investment in Unconsolidated Joint Ventures (Details 3) (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
Assets
Commercial real estate property, net	$ 10,242,225		$ 10,242,225		$ 10,010,548
Other assets	784,901		784,901		737,900
Liabilities and members' equity
Mortgages and other loans payable	4,861,463		4,861,463		4,314,741
Company's net investment in unconsolidated joint ventures	1,014,042		1,014,042		893,933
Combined statements of income for the unconsolidated joint ventures
Operating expense	68,919	62,395	142,188	122,698
Real estate taxes	52,569	43,975	104,067	84,042
Interest expense, net of interest income	82,327	68,173	162,464	132,439
Depreciation and amortization			162,028	136,355
Transaction related costs	1,970	1,217	3,121	3,651
Total expenses	316,761	275,530	633,045	534,601
Company's equity in net (loss) income of unconsolidated joint ventures	70,890	2,184	69,330	10,390
Joint venture
Assets
Commercial real estate property, net	6,153,652		6,153,652		5,699,113
Other assets	668,567		668,567		599,596
Total assets	6,822,219		6,822,219		6,298,709
Liabilities and members' equity
Mortgages and other loans payable	4,695,103		4,695,103		4,131,890
Other liabilities	271,289		271,289		250,925
Members' equity	1,855,827		1,855,827		1,915,894
Total liabilities and members equity	6,822,219		6,822,219		6,298,709
Company's net investment in unconsolidated joint ventures	1,014,042		1,014,042		893,933
Combined statements of income for the unconsolidated joint ventures
Total revenues	124,418	113,792	244,466	237,352
Operating expense	16,949	16,080	34,633	36,681
Real estate taxes	12,483	12,290	25,857	25,740
Interest expense, net of interest income	53,506	53,587	110,141	101,224
Depreciation and amortization	35,724	33,865	72,507	65,589
Transaction related costs	90	752	358	817
Total expenses	118,752	116,574	243,496	230,051
Net income (loss)	5,666	(2,782)	970	7,301
Company's equity in net (loss) income of unconsolidated joint ventures	$ 70,890	$ 2,184	$ 69,330	$ 10,390