CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net income		$ 78,847		$ 147,717	$ 669,058	$ 486,592
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation expense		193,791		175,348	561,560	529,508
Amortization of deferred financing costs					5,519	5,617
Amortization of debt discount					1,998	1,321
Loss on extinguishment of debt, net		(17,890)		105	(17,768)	(9,333)
Amortization of stock-based compensation					20,660	17,753
Equity in loss of, and return on, unconsolidated real estate entities and noncontrolling interests, net of eliminations					4,290	5,204
Real estate casualty loss					2,802	0
Abandonment of development pursuits					685	2,095
Unrealized gain on terminated cash flow hedges			$ (2,654)		(2,654)	0	$ 2,894
Cash flow hedge losses reclassified to earnings					6,874	6,617
Gain on sale of real estate assets					(413,661)	(96,823)
Gain on for-sale condominiums					(2,051)	(8,174)
Increase in resident security deposits, prepaid expenses and other assets					(20,555)	(36,332)
Increase in accrued expenses, other liabilities and accrued interest payable					59,449	39,363
Net cash provided by operating activities					911,742	962,074
Cash flows from investing activities:
Development/redevelopment of real estate assets including land acquisitions and deferred development costs					(476,307)	(562,334)
Acquisition of real estate assets, including partnership interest					(392,746)	0
Capital expenditures - existing real estate assets					(105,621)	(76,860)
Capital expenditures - non-real estate assets					(4,689)	(24,720)
Decrease in payables for construction					(35,639)	(4,095)
Proceeds from sale of real estate, net of selling costs					576,973	186,090
Proceeds from the sale of for-sale condominiums, net of selling costs					98,752	170,604
Mortgage note receivable lending					(118)	(260)
Mortgage note receivable payments					1,556	3,419
Distributions from unconsolidated real estate entities					62,157	9,877
Investments in unconsolidated real estate entities					(40,071)	(23,044)
Net cash used in investing activities					(315,753)	(321,323)
Cash flows from financing activities:
Issuance of common stock, net					7,011	1,599
Repurchase of common stock, net					0	(137,458)
Dividends paid					(666,420)	(661,000)
Issuance of mortgage notes payable					0	51,000
Repayments of mortgage notes payable, including prepayment penalties					(35,688)	(125,427)
Issuance of unsecured notes					699,167	1,296,581
Repayment of unsecured notes, including prepayment penalties					(462,147)	(958,681)
Payment of deferred financing costs					(5,281)	(11,278)
Receipt (payment) for termination of forward interest rate swaps	$ (2,211)		6,962		4,751	(25,135)
Payment to noncontrolling interest					(45)	(59)
Payments related to tax withholding for share-based compensation					(13,409)	(14,752)
Distributions to DownREIT partnership unitholders					(36)	(36)
Distributions to joint venture and profit-sharing partners					(234)	(319)
Preferred interest obligation redemption and dividends					(1,340)	(1,000)
Net cash used in financing activities					(473,671)	(585,965)
Net increase in cash, cash equivalents and cash in escrow					122,318	54,786
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Beginning Balance			$ 313,532		313,532	127,614	127,614
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance	435,850	435,850		182,400	435,850	182,400	313,532
Cash paid during the period for interest, net of amount capitalized					127,575	133,913
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	322,294	322,294		87,530	322,294	87,530	216,976
Cash in escrow	113,556	113,556		94,870	113,556	94,870	96,556
Cash, cash equivalents and cash in escrow reported in the Condensed Consolidated Statements of Cash Flows	$ 435,850	$ 435,850		$ 182,400	$ 435,850	$ 182,400	$ 313,532