CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income	$ 441,370,000	$ 174,079,000	$ 154,274,000
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation expense	246,666,000	227,878,000	204,481,000
Depreciation expense from discontinued operations	3,603,000	5,064,000	13,805,000
Amortization of deferred financing costs and debt premium/discount	5,834,000	7,723,000	8,139,000
Amortization of stock-based compensation	7,244,000	5,938,000	6,098,000
Equity in (income) loss of unconsolidated entities and noncontrolling interests, net of eliminations	2,246,000	1,852,000	(810,000)
Impairment loss	14,052,000		21,152,000
Abandonment of development pursuit			2,461,000
Loss on extinguishment of debt, net	5,820,000		25,910,000
Gain on sale of real estate assets	(294,806,000)	(74,074,000)	(68,717,000)
Expensed acquisition costs	1,010,000
Increase in cash in operating escrows	(7,702,000)	(4,996,000)	(2,434,000)
(Increase) decrease in resident security deposits, prepaid expenses and other assets	(4,991,000)	(15,234,000)	372,000
Increase in accrued expenses, other liabilities and accrued interest payable	9,045,000	3,876,000	11,850,000
Net cash provided by operating activities	429,391,000	332,106,000	376,581,000
Cash flows from investing activities:
Development/redevelopment of real estate assets including land acquisitions and deferred development costs	(640,778,000)	(429,853,000)	(560,155,000)
Acquisition of communities	(46,275,000)
Capital expenditures - existing real estate assets	(41,851,000)	(16,772,000)	(11,114,000)
Capital expenditures - non-real estate assets	(8,281,000)	(420,000)	(834,000)
Proceeds from exchange/sale of real estate, net of selling costs	310,228,000	194,009,000	189,417,000
Increase (decrease) in payables for construction	2,342,000	(15,190,000)	(14,740,000)
Decrease in cash in construction escrows	14,109,000	42,329,000	77,754,000
Acquisition of mortgage note	(1,701,000)	(24,000,000)
Increase in investments in unconsolidated real estate entities	(30,934,000)	(49,039,000)	(13,887,000)
Net cash used in investing activities	(443,141,000)	(298,936,000)	(333,559,000)
Cash flows from financing activities:
Issuance of common stock	1,049,835,000	381,365,000	108,860,000
Dividends paid	(318,231,000)	(298,090,000)	(283,710,000)
Net repayments under unsecured credit facility			(124,000,000)
Issuance of mortgage notes payable and draws on construction loans			741,140,000
Repayments of mortgage notes payable	(200,166,000)	(69,327,000)	(65,229,000)
Issuance of unsecured notes		250,000,000	500,000,000
Repayment of unsecured notes	(189,900,000)	(89,576,000)	(868,564,000)
Payment of deferred financing costs	(5,996,000)	(6,524,000)	(12,523,000)
Redemption of units for cash by minority partners	(25,000)		(202,000)
Acquisition of joint venture partner equity interest	(9,070,000)
Distributions to DownREIT partnership unitholders	(20,000)	(61,000)	(57,000)
Distributions to joint venture and profit-sharing partners	(194,000)	(222,000)
Net cash provided by (used in) financing activities	326,233,000	167,565,000	(4,285,000)
Net increase in cash and cash equivalents	312,483,000	200,735,000	38,737,000
Cash and cash equivalents, beginning of year	304,407,000	103,672,000	64,935,000
Cash and cash equivalents, end of year	616,890,000	304,407,000	103,672,000
Cash paid during the year for interest, net of amount capitalized	$ 156,898,000	$ 157,014,000	$ 168,651,000