Investments in Partially Owned Entities (Details) (USD $) In Thousands, unless otherwise specified					9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Dec. 31, 2009	Sep. 30, 2011 Co-invested in various properties with unrelated third parties [Member] Project Apartment	Sep. 30, 2011 Co-invested in various properties with unrelated third parties [Member] Consolidated Development Projects Held for and or Under Development [Member] Project Apartment	Sep. 30, 2011 Co-invested in various properties with unrelated third parties [Member] Consolidated Development Projects Completed and Stabilized [Member] Project Apartment	Sep. 30, 2011 Co-invested in various properties with unrelated third parties [Member] Consolidated Other [Member] Project Apartment
Partially Owned Property Balance Sheet Schedule
Total projects					21	0	2	19
Total apartment units					3,916	0	441	3,475
ASSETS
Investment in real estate	$ 19,538,767	$ 19,702,371			$ 587,580	$ 25,071	$ 114,570	$ 447,939
Accumulated depreciation	(4,405,479)	(4,337,357)			(151,630)	0	(11,186)	(140,444)
Investment in real estate, net	15,133,288	15,365,014			435,950	25,071	103,384	307,495
Cash and cash equivalents	45,986	431,408	43,660	193,288	14,299	1,643	1,578	11,078
Deposits - restricted	369,461	180,987			17,544	0	2,367	15,177
Escrow deposits - mortgage	10,677	12,593			50	0	50	0
Deferred financing costs, net	37,334	42,033			1,306	0	119	1,187
Other assets	149,051	148,992			357	89	132	136
Total assets	15,756,817	16,184,194			469,506	26,803	107,630	335,073
LIABILITIES AND EQUITY
Accounts payable and accrued expenses	97,845	39,452			4,466	179	1,327	2,960
Accrued interest payable	69,895	98,631			978	0	258	720
Other liabilities	409,591	304,202			4,183	1,274	47	2,862
Security deposits	62,073	60,812			1,592	0	110	1,482
Total liabilities	9,523,248	10,592,078			295,709	1,453	85,895	208,361
Noncontrolling Interests - Partially Owned Properties					(1,714)	2,243	1,079	(5,036)
Company equity/General and Limited Partners' capital					175,511	23,107	20,656	131,748
Total equity/capital					173,797	25,350	21,735	126,712
Total liabilities and equity	15,756,817	16,184,194			469,506	26,803	107,630	335,073
Debt-Secured:
Company/Operating Partnership Ownership					243,221		84,153	159,068
Noncontrolling Ownership					41,269			41,269
Carrying value of the mortgage notes payable	$ 4,136,848	$ 4,762,896			$ 284,490	$ 0	$ 84,153	$ 200,337