Investments in Real Estate Entities - Financial Position and Operating Results (Details) ft² in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) home ft²	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) home ft²	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
ASSETS
Real estate, net	$ 18,297,701,000		$ 18,297,701,000		$ 18,432,989,000
Total assets	19,144,611,000		19,144,611,000		19,121,051,000
LIABILITIES AND EQUITY
Mortgage notes payable, net	863,396,000		863,396,000		937,642,000
Partners' capital	10,669,644,000		10,669,644,000		10,989,549,000
Total liabilities and equity	19,144,611,000		19,144,611,000		19,121,051,000
Combined summary of the operating results of the accounted for using the equity method
Rental and other income	567,404,000	$ 587,613,000	1,745,459,000	$ 1,731,060,000
Operating and other expenses	(455,887,000)	(427,812,000)	(1,362,534,000)	(1,265,927,000)
Gain on sale of communities	31,607,000	130,484,000	91,338,000	165,849,000
Interest expense, net	(53,249,000)	(51,493,000)	(162,562,000)	(149,395,000)
Depreciation expense	(175,348,000)	(165,463,000)	(529,508,000)	(490,213,000)
Net income	147,717,000	279,709,000	486,592,000	618,432,000
Equity Method Investment, Net Income (Loss), Portion Attributable To Parent	5,611,000	2,175,000	8,357,000	2,377,000
Equity Method Investments, Amortization Of Excess Investment And Other	(528,000)	(532,000)	(1,587,000)	(1,597,000)
Equity in income of unconsolidated real estate entities	$ 5,083,000	1,643,000	$ 6,770,000	780,000
Avalon Venice on Rose [Member]
Combined summary of the operating results of the accounted for using the equity method
Commercial Square Feet | ft²	9		9
Avalon Venice on Rose [Member] | Notes Payable Maturities 2020 [Member] | Secured Debt [Member]
Combined summary of the operating results of the accounted for using the equity method
Repayments of Secured Debt			$ 27,117,000
US Fund [Member]
Combined summary of the operating results of the accounted for using the equity method
Proceeds from Sale of Real Estate			$ 65,000,000
US Fund [Member] | Avalon Venice on Rose [Member]
Combined summary of the operating results of the accounted for using the equity method
Number Of Apartment Homes Sold | home			70
Equity Method Investment, Realized Gain (Loss) on Disposal			$ 5,157,000
AVA Arts District [Member]
Combined summary of the operating results of the accounted for using the equity method
Number Of operating apartment communities owned | home	475		475
Ownership percentage	25.00%		25.00%
Equity method investments	$ 14,800,000		$ 14,800,000
Long-term Construction Loan	$ 165,600,000		$ 165,600,000
Real Estate Investments, Percent Of Development Funded By Borrowings	60.00%		60.00%
Proceeds from construction loans			$ 0
AVA Arts District [Member] | Maximum
Combined summary of the operating results of the accounted for using the equity method
Equity method investments	$ 27,600,000		$ 27,600,000
AVA Arts District [Member] | Joint Venture Partner [Member]
Combined summary of the operating results of the accounted for using the equity method
Ownership percentage	75.00%		75.00%
Equity Method Investment, Nonconsolidated Investee or Group of Investees
ASSETS
Real estate, net	$ 1,222,762,000		$ 1,222,762,000		1,204,470,000
Other assets	265,048,000		265,048,000		196,488,000
Total assets	1,487,810,000		1,487,810,000		1,400,958,000
LIABILITIES AND EQUITY
Mortgage notes payable, net	749,555,000		749,555,000		782,257,000
Other liabilities	158,875,000		158,875,000		157,379,000
Partners' capital	579,380,000		579,380,000		461,322,000
Total liabilities and equity	1,487,810,000		1,487,810,000		$ 1,400,958,000
Combined summary of the operating results of the accounted for using the equity method
Rental and other income	28,800,000	37,382,000	92,299,000	108,635,000
Operating and other expenses	(12,782,000)	(14,535,000)	(37,034,000)	(42,624,000)
Gain on sale of communities	18,408,000	0	18,448,000	0
Interest expense, net	(8,024,000)	(8,385,000)	(24,133,000)	(25,482,000)
Depreciation expense	(8,704,000)	(9,324,000)	(26,106,000)	(49,366,000)
Net income	$ 17,698,000	$ 5,138,000	$ 23,474,000	$ (8,837,000)