Investments in Partially Owned Entities (Details) (USD $) In Thousands, unless otherwise specified					6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2009	Jun. 30, 2011 Co-invested in various properties with unrelated third parties [Member]	Jun. 30, 2011 Co-invested in various properties with unrelated third parties [Member] Consolidated Development Projects Held for and or Under Development [Member]	Jun. 30, 2011 Co-invested in various properties with unrelated third parties [Member] Consolidated Development Projects Completed and Stabilized [Member]	Jun. 30, 2011 Co-invested in various properties with unrelated third parties [Member] Consolidated Other [Member]
Partially Owned Property Balance Sheet Schedule
Total projects					22		3	19
Total units					4,371		931	3,440
ASSETS
Investment in real estate	$ 19,537,188	$ 19,702,371			$ 842,122	$ 25,067	$ 376,257	$ 440,998
Accumulated depreciation	(4,307,406)	(4,337,357)			(145,774)	0	(13,937)	(131,837)
Investment in real estate, net	15,229,782	15,365,014			696,348	25,067	362,120	309,161
Cash and cash equivalents	604,764	431,408	47,982	193,288	13,174	527	2,870	9,777
Deposits - restricted	361,831	180,987			27,567	1,120	3,560	22,887
Escrow deposits - mortgage	10,905	12,593			48	0	48	0
Deferred financing costs, net	35,451	42,033			2,775	0	1,791	984
Other assets	151,766	148,992			413	126	181	106
Total assets	16,398,122	16,184,194			740,325	26,840	370,570	342,915
LIABILITIES AND EQUITY
Accounts payable and accrued expenses	69,118	39,452			2,925	253	1,106	1,566
Accrued interest payable	92,584	98,631			906		333	573
Other liabilities	306,503	304,202			2,992	1,277	558	1,157
Security deposits	60,779	60,812			2,775		1,306	1,469
Total liabilities	10,084,172	10,592,078			424,765	1,530	235,833	187,402
Noncontrolling Interests - Partially Owned Properties					3,295	2,179	6,104	(4,988)
Company equity/General and Limited Partners' capital					312,265	23,131	128,633	160,501
Total equity/capital					315,560	25,310	134,737	155,513
Total liabilities and equity	16,398,122	16,184,194			740,325	26,840	370,570	342,915
Debt-Secured:
Company/Operating Partnership					384,574	0	232,530	152,017
Noncontrolling Ownership					30,620	0	0	30,620
Total Debt	$ 4,352,372	$ 4,762,896			$ 415,167	$ 0	$ 232,530	$ 182,637