Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jan. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net income			$ 105,700	$ 86,110	$ 329,266	$ 289,159
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization					360,842	359,287
Amortization of discount on marketable securities					(16,673)	(12,949)
Amortization of discount (premium) and debt financing costs, net					3,454	(1,958)
Gain on sale of marketable securities					(737)	(669)
Unrealized (gain) loss on equity securities recognized through income					(4,280)	(426)
Company's share of gain on the sales of co-investments					(870)	0
Earnings from co-investments					(54,065)	(64,611)
Operating distributions from co-investments					64,628	80,232
Accrued interest from notes and other receivables					(4,523)	(4,016)
Gain on the sale of real estate and land					0	(22,244)
Equity-based compensation					6,748	7,209
Gain on early retirement of debt, net	$ (5,500)	$ (1,400)	(5,475)	0	(7,143)	0
Gain on remeasurement of co-investment			0	0	(31,535)	0
Changes in operating assets and liabilities:
Prepaid expenses, receivables, operating lease right-of-use assets, and other assets					(4,192)	(4,044)
Accounts payable, accrued liabilities, and operating lease liabilities					64,281	55,469
Other liabilities					1,726	698
Net cash provided by operating activities					706,927	681,137
Additions to real estate:
Acquisitions of real estate and acquisition related capital expenditures					(93,389)	(7,807)
Redevelopment					(55,027)	(54,656)
Development acquisitions of and additions to real estate under development					(130,593)	(131,867)
Capital expenditures on rental properties					(69,348)	(54,890)
Investments in notes receivable					(140,663)	0
Collections of notes and other receivables					2,500	29,500
Proceeds from insurance for property losses					3,599	1,237
Proceeds from dispositions of real estate					0	130,730
Contributions to co-investments					(306,233)	(100,202)
Changes in refundable deposits					325	(3,804)
Purchases of marketable securities					(42,653)	(29,130)
Sales and maturities of marketable securities					57,165	22,501
Non-operating distributions from co-investments					70,064	62,564
Net cash used in investing activities					(704,253)	(135,824)
Cash flows from financing activities:
Proceeds from unsecured debt and mortgage notes					892,762	298,773
Payments on unsecured debt and mortgage notes					(800,746)	(162,317)
Proceeds from lines of credit					1,485,034	454,170
Repayments of lines of credit					(1,265,034)	(633,170)
Retirement of common stock					(56,989)	(3,774)
Additions to deferred charges					(9,446)	(4,093)
Net proceeds from issuance of common stock					72,549	(483)
Net proceeds from stock options exercised					36,422	2,751
Payments related to tax withholding for share-based compensation					(3,515)	(23)
Distributions to noncontrolling interest					(20,269)	(22,137)
Redemption of noncontrolling interest					(14,180)	(157)
Redemption of redeemable noncontrolling interest					(73)	(43)
Common and preferred stock dividends paid					(378,858)	(361,310)
Net cash used in financing activities					(62,343)	(431,813)
Net (decrease) increase in unrestricted and restricted cash and cash equivalents					(59,669)	113,500
Unrestricted and restricted cash and cash equivalents at beginning of period		151,395			151,395	61,126	$ 61,126
Unrestricted and restricted cash and cash equivalents at end of period	91,726		91,726	174,626	91,726	174,626	151,395
Supplemental disclosure of cash flow information:
Cash paid for interest (net of $19.0 million and $13.3 million capitalized in 2019 and 2018, respectively)					145,001	146,039
Operating cash flows from operating leases					5,097	0
Supplemental disclosure of noncash investing and financing activities:
Issuance of DownREIT limited partnership units in connection with acquisition of real estate					65,472	0
Transfers between real estate under development to rental properties, net					14,501	99,547
Transfer from real estate under development to co-investments					106	640
Reclassifications to redeemable noncontrolling interest from additional paid in capital and noncontrolling interest					3,675	2,253
Redemption of redeemable noncontrolling interest via reduction of note receivable					0	4,751
Initial recognition of operating lease right-of-use assets					77,645	0
Initial recognition of operating lease liabilities					79,693	0
Debt assumed in connection with acquisition					143,006	0
Repayment of mortgage note from new financing proceeds					0	52,000
Essex Portfolio, L.P. [Member]
Cash flows from operating activities:
Net income			105,700	86,110	329,266	289,159
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization					360,842	359,287
Amortization of discount on marketable securities					(16,673)	(12,949)
Amortization of discount (premium) and debt financing costs, net					3,454	(1,958)
Gain on sale of marketable securities					(737)	(669)
Unrealized (gain) loss on equity securities recognized through income					(4,280)	(426)
Company's share of gain on the sales of co-investments					(870)	0
Earnings from co-investments					(54,065)	(64,611)
Operating distributions from co-investments					64,628	80,232
Accrued interest from notes and other receivables					(4,523)	(4,016)
Gain on the sale of real estate and land					0	(22,244)
Equity-based compensation					6,748	7,209
Gain on early retirement of debt, net			(5,475)	0	(7,143)	0
Gain on remeasurement of co-investment			0	0	(31,535)	0
Changes in operating assets and liabilities:
Prepaid expenses, receivables, operating lease right-of-use assets, and other assets					(4,192)	(4,044)
Accounts payable, accrued liabilities, and operating lease liabilities					64,281	55,469
Other liabilities					1,726	698
Net cash provided by operating activities					706,927	681,137
Additions to real estate:
Acquisitions of real estate and acquisition related capital expenditures					(93,389)	(7,807)
Redevelopment					(55,027)	(54,656)
Development acquisitions of and additions to real estate under development					(130,593)	(131,867)
Capital expenditures on rental properties					(69,348)	(54,890)
Investments in notes receivable					(140,663)	0
Collections of notes and other receivables					2,500	29,500
Proceeds from insurance for property losses					3,599	1,237
Proceeds from dispositions of real estate					0	130,730
Contributions to co-investments					(306,233)	(100,202)
Changes in refundable deposits					325	(3,804)
Purchases of marketable securities					(42,653)	(29,130)
Sales and maturities of marketable securities					57,165	22,501
Non-operating distributions from co-investments					70,064	62,564
Net cash used in investing activities					(704,253)	(135,824)
Cash flows from financing activities:
Proceeds from unsecured debt and mortgage notes					892,762	298,773
Payments on unsecured debt and mortgage notes					(800,746)	(162,317)
Proceeds from lines of credit					1,485,034	454,170
Repayments of lines of credit					(1,265,034)	(633,170)
Retirement of common stock					(56,989)	(3,774)
Additions to deferred charges					(9,446)	(4,093)
Net proceeds from issuance of common stock					72,549	(483)
Net proceeds from stock options exercised					36,422	2,751
Payments related to tax withholding for share-based compensation					(3,515)	(23)
Distributions to noncontrolling interest					(5,978)	(6,615)
Redemption of noncontrolling interest					(14,180)	(157)
Redemption of redeemable noncontrolling interest					(73)	(43)
Common and preferred stock dividends paid					(393,149)	(376,832)
Net cash used in financing activities					(62,343)	(431,813)
Net (decrease) increase in unrestricted and restricted cash and cash equivalents					(59,669)	113,500
Unrestricted and restricted cash and cash equivalents at beginning of period		$ 151,395			151,395	61,126	61,126
Unrestricted and restricted cash and cash equivalents at end of period	$ 91,726		$ 91,726	$ 174,626	91,726	174,626	$ 151,395
Supplemental disclosure of cash flow information:
Cash paid for interest (net of $19.0 million and $13.3 million capitalized in 2019 and 2018, respectively)					145,001	146,039
Operating cash flows from operating leases					5,097	0
Supplemental disclosure of noncash investing and financing activities:
Issuance of DownREIT limited partnership units in connection with acquisition of real estate					65,472	0
Transfers between real estate under development to rental properties, net					14,501	99,547
Transfer from real estate under development to co-investments					106	640
Reclassifications to redeemable noncontrolling interest from additional paid in capital and noncontrolling interest					3,675	2,253
Redemption of redeemable noncontrolling interest via reduction of note receivable					0	4,571
Initial recognition of operating lease right-of-use assets					77,645	0
Initial recognition of operating lease liabilities					79,693	0
Debt assumed in connection with acquisition					143,006	0
Repayment of mortgage note from new financing proceeds					$ 0	$ 52,000