CONSOLIDATED STATEMENTS OF CASH FLOWS OF ERP OPERATING LIMITED PARTNERSHIP (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 496,805	$ 827,796
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	516,940	496,383
Amortization of deferred financing costs	10,384	12,769
Amortization of discounts and premiums on debt	(5,795)	144
Amortization of deferred settlements on derivative instruments	10,506	2,441
Write-off of pursuit costs	6,141	4,052
IncomeFromTechnologyInvestments	0	(4,537)
Distributions from unconsolidated entities - return on capital	454	318
Net (Gain) On Sale Of Land Parcels	0	(4,217)
Net (gain) on sales of discontinued operations	(307,447)	(759,100)
Loss on debt extinguishment	272	0
Unrealized (gain) loss on derivative instruments	(1)	0
Compensation paid with Company Common Shares	20,836	16,722
Changes in assets and liabilities:
(Increase) decrease in deposits - restricted	(2,250)	5,101
(Increase) in other assets	(14,039)	3,239
Increase in accounts payable and accrued expenses	67,479	60,608
(Decrease) in accrued interest payable	(9,252)	(28,736)
Increase (decrease) in other liabilities	68,492	(20,193)
Increase in security deposits	3,472	1,261
Net cash provided by operating activities	863,000	614,051
CASH FLOWS FROM INVESTING ACTIVITIES:
Investment in real estate - acquisitions	(764,859)	(634,581)
Investment in real estate - development/other	(116,715)	(93,761)
Improvements to real estate	(114,535)	(106,070)
Additions to non-real estate property	(6,716)	(4,879)
Interest capitalized for real estate and unconsolidated entities under development	(15,776)	(5,931)
Proceeds from disposition of real estate, net	610,127	1,402,475
Investments in unconsolidated entities	(5,423)	(865)
ProceedsFromTechnologyInvestments	0	4,537
(Increase) in deposits on real estate acquisitions and investments, net	31,677	(210,170)
Decrease in mortgage deposits	230	1,916
ProceedsFromSaleOfEquityInterest	0	28,360
Acquisition of Noncontrolling Interests - Partially Owned Properties	(87)	(12,809)
Net cash (used for) provided by investing activities	(382,077)	368,222
CASH FLOWS FROM FINANCING ACTIVITIES:
Loan and bond acquisition costs	(4,599)	(8,070)
Mortgage notes payable:
Proceeds	0	152,930
Restricted cash	2,370	16,595
Scheduled principal repayments	(11,022)	(12,463)
Loss on debt extinguishments	(272)	0
Notes, net:
Lump sum payoffs	(253,858)	(575,641)
Line of Credit Facility:
Proceeds	392,000	213,000
Repayments	385,000	187,000
Proceeds from exercise of EQR options	46,781	94,373
Redemption of Preferred Shares Preference Units	(150,000)	0
Premium on Redemption of Preferred Shares Cash	(21)	0
Payment of offering costs	(2,860)	(2,770)
Other financing activities, net	(33)	(33)
Contributions - Noncontrolling Interests - Partially Owned Properties	5,992	64
Contributions - Noncontrolling Interests - Operating Partnership	5	0
Distributions:
Noncontrolling Interests – Partially Owned Properties	(4,742)	(889)
Net cash (used for) financing activities	(819,221)	(1,367,695)
Net (decrease) increase in cash and cash equivalents	(338,298)	(385,422)
Cash and cash equivalents, beginning of period	383,921	431,408
Cash and cash equivalents, end of period	45,623	45,986
SUPPLEMENTAL INFORMATION:
Cash paid for interest, net of amounts capitalized	353,329	381,194
Net cash paid for income and other taxes	573	607
Real estate acquisitions/dispositions/other:
Mortgage loans assumed	137,644	99,131
Valuation Of OP Units Issued	66,606	0
Amortization of discounts and premiums on debt:
Mortgage notes payable	(7,462)	(6,116)
Notes, net	1,667	6,260
Amortization of deferred settlements on derivative instruments:
Other liabilities	(401)	(401)
Accumulated other comprehensive income	(10,907)	(2,842)
Unrealized (gain) loss on derivative instruments:
Other assets	5,934	5,217
Mortgage notes payable	(2,589)	(464)
Notes, net	(3,345)	(1,476)
Other liabilities	12,336	127,090
Unrealized holding (losses) arising during the period	(12,337)	(130,367)
Interest capitalized for real estate and unconsolidated entities under development:
Investment in real estate, net	(15,163)	(5,760)
Investment in unconsolidated entities	(613)	(171)
DeconsolidationOfPreviouslyConsolidatedProperties [Abstract]
DeconsolidationOfPreviouslyConsolidatedPropertiesInvestmentInRealEstateNet	0	35,495
DeconsolidationOfPreviouslyConsolidatedPropertiesInvestmentsInUnconsolidatedEntitie	0	(7,135)
OPERATING PARTNERSHIP
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	496,805	827,796
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	516,940	496,383
Amortization of deferred financing costs	10,384	12,769
Amortization of discounts and premiums on debt	(5,795)	144
Amortization of deferred settlements on derivative instruments	10,506	2,441
Write-off of pursuit costs	6,141	4,052
Distributions from unconsolidated entities - return on capital	454	318
Net (Gain) On Sale Of Land Parcels	0	(4,217)
Net (gain) on sales of discontinued operations	(307,447)	(759,100)
Unrealized (gain) loss on derivative instruments	(1)	0
Compensation paid with Company Common Shares	20,836	16,722
Changes in assets and liabilities:
(Increase) decrease in deposits - restricted	(2,250)	5,101
(Increase) in other assets	(14,039)	3,239
Increase in accounts payable and accrued expenses	67,479	60,608
(Decrease) in accrued interest payable	(9,252)	(28,736)
Increase (decrease) in other liabilities	68,492	(20,193)
Increase in security deposits	3,472	1,261
Net cash provided by operating activities	863,000	614,051
CASH FLOWS FROM INVESTING ACTIVITIES:
Investment in real estate - acquisitions	(764,859)	(634,581)
Investment in real estate - development/other	(116,715)	(93,761)
Improvements to real estate	(114,535)	(106,070)
Additions to non-real estate property	(6,716)	(4,879)
Interest capitalized for real estate and unconsolidated entities under development	(15,776)	(5,931)
Proceeds from disposition of real estate, net	610,127	1,402,475
Investments in unconsolidated entities	(5,423)	(865)
(Increase) in deposits on real estate acquisitions and investments, net	31,677	(210,170)
Decrease in mortgage deposits	230	1,916
ProceedsFromSaleOfEquityInterest	0	28,360
Acquisition of Noncontrolling Interests - Partially Owned Properties	(87)	(12,809)
Net cash (used for) provided by investing activities	(382,077)	368,222
CASH FLOWS FROM FINANCING ACTIVITIES:
Loan and bond acquisition costs	(4,599)	(8,070)
Mortgage notes payable:
Proceeds	0	152,930
Restricted cash	2,370	16,595
Lump sum payoffs	(279,943)	(859,066)
Scheduled principal repayments	(11,022)	(12,463)
Notes, net:
Lump sum payoffs	(253,858)	(575,641)
Line of Credit Facility:
Proceeds	392,000	213,000
Repayments	(385,000)	(187,000)
Proceeds from sale of OP Units	220,753	154,508
Proceeds from EQR's Employee Share Purchase Plan (ESPP)	4,944	4,558
Proceeds from exercise of EQR options	46,781	94,373
Payment of offering costs	(2,860)	(2,770)
Contributions - Noncontrolling Interests - Partially Owned Properties	5,992	64
Contributions - Noncontrolling Interests - Operating Partnership	5	0
Distributions:
OP Units - General Partner	(371,319)	(331,928)
Preference Units	(11,344)	(10,399)
OP Units - Limited Partners	(17,053)	(15,464)
Noncontrolling Interests – Partially Owned Properties	(4,742)	(889)
Net cash (used for) financing activities	(819,221)	(1,367,695)
Net (decrease) increase in cash and cash equivalents	(338,298)	(385,422)
Cash and cash equivalents, beginning of period	383,921	431,408
Cash and cash equivalents, end of period	45,623	45,986
SUPPLEMENTAL INFORMATION:
Cash paid for interest, net of amounts capitalized	353,329	381,194
Net cash paid for income and other taxes	573	607
Real estate acquisitions/dispositions/other:
Mortgage loans assumed	137,644	99,131
Amortization of discounts and premiums on debt:
Mortgage notes payable	(7,462)	(6,116)
Notes, net	1,667	6,260
Amortization of deferred settlements on derivative instruments:
Other liabilities	(401)	(401)
Accumulated other comprehensive income	10,907	2,842
Unrealized (gain) loss on derivative instruments:
Other assets	5,934	5,217
Mortgage notes payable	(2,589)	(464)
Notes, net	(3,345)	(1,476)
Other liabilities	12,336	127,090
Unrealized holding (losses) arising during the period	(12,337)	(130,367)
Interest capitalized for real estate and unconsolidated entities under development:
Investment in real estate, net	(15,163)	(5,760)
Investment in unconsolidated entities	(613)	(171)
Other:
Receivable on sale of OP Units	$ 28,457	$ 0