CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 423,562	$ 441,370	$ 174,079
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation expense	256,026	239,060	220,563
Depreciation expense from discontinued operations	4,068	11,209	12,379
Amortization of deferred financing costs and debt premium/discount	6,427	5,834	7,723
Amortization of stock-based compensation	8,707	7,244	5,938
Cash flow hedge losses reclassified to earnings	1,889
Equity in (income) loss of, and return on unconsolidated entities and noncontrolling interests, net of eliminations	(12,103)	2,246	1,852
Loss on extinguishment of debt, net	1,781	5,820
Casualty loss and impairment of real estate assets	1,449	14,052
Gain on sale of real estate assets	(146,591)	(294,806)	(74,074)
Gain on acquisition of unconsolidated entity	(14,194)
Expensed acquisition costs	9,593	1,010
(Increase) decrease in cash in operating escrows	6,543	(7,702)	(4,996)
Increase in resident security deposits, prepaid expenses and other assets	(1,601)	(5,028)	(15,234)
(Decrease) increase in accrued expenses, other liabilities and accrued interest payable	(4,737)	9,045	3,876
Net cash provided by operating activities	540,819	429,354	332,106
Cash flows from investing activities:
Development/redevelopment of real estate assets including land acquisitions and deferred development costs	(755,363)	(640,778)	(429,853)
Acquisition of real estate assets, including partnership interest	(155,755)	(46,275)
Capital expenditures - existing real estate assets	(23,452)	(41,851)	(16,772)
Capital expenditures - non-real estate assets	(3,076)	(8,281)	(420)
Proceeds from exchange/sale of real estate, net of selling costs	274,018	310,228	194,009
Increase (decrease) in payables for construction	16,832	2,342	(15,190)
Decrease in cash in construction escrows	16,824	14,109	42,329
Acquisition of mortgage note		(1,701)	(24,000)
Decrease (increase) in investments in unconsolidated real estate entities	6,586	(30,934)	(49,039)
Net cash used in investing activities	(623,386)	(443,141)	(298,936)
Cash flows from financing activities:
Issuance of common stock	2,430,190	1,049,835	381,365
Dividends paid	(365,572)	(318,231)	(298,090)
Repayments of mortgage notes payable	(110,013)	(200,166)	(69,327)
Issuance of unsecured notes	700,000		250,000
Settlement of interest rate contract	(54,930)
Repayment of unsecured notes	(381,001)	(189,900)	(89,576)
Payment of deferred financing costs and issuance discounts	(15,664)	(5,996)	(6,524)
Redemption of units for cash by minority partners		(25)
Acquisition of joint venture partner equity interest	(3,350)	(9,070)
Distributions to DownREIT partnership unitholders	(29)	(20)	(61)
Distributions to joint venture and profit-sharing partners	(299)	(194)	(222)
Net cash provided by financing activities	2,199,332	326,233	167,565
Net increase in cash and cash equivalents	2,116,765	312,446	200,735
Cash and cash equivalents, beginning of year	616,853	304,407	103,672
Cash and cash equivalents, end of year	2,733,618	616,853	304,407
Cash paid during the year for interest, net of amount capitalized	$ 119,268	$ 156,898	$ 157,014