Segment Reporting (Details 3) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting
Total revenue	$ 567,404	$ 587,613	$ 1,745,459	$ 1,731,060
NOI	377,678	406,585	1,201,966	1,200,119
Gross real estate	23,941,920	22,991,068	23,941,920	22,991,068
Operating Segments | Established
Segment Reporting
Total revenue	508,558	541,737	1,572,701	1,605,891
NOI	342,942	381,654	1,097,902	1,139,773
Gross real estate	19,325,453	19,190,276	19,325,453	19,190,276
Operating Segments | Established | New England
Segment Reporting
Total revenue	78,057	81,924	239,456	240,178
NOI	49,089	54,244	155,604	158,801
Gross real estate	2,774,519	2,742,940	2,774,519	2,742,940
Operating Segments | Established | Metro NY/NJ
Segment Reporting
Total revenue	112,507	119,857	344,475	355,990
NOI	75,193	82,602	236,138	248,530
Gross real estate	4,303,971	4,284,077	4,303,971	4,284,077
Operating Segments | Established | Mid-Atlantic
Segment Reporting
Total revenue	84,038	88,829	259,086	262,806
NOI	56,190	62,430	180,886	185,431
Gross real estate	3,505,272	3,475,939	3,505,272	3,475,939
Operating Segments | Established | Pacific Northwest
Segment Reporting
Total revenue	27,125	28,589	83,539	84,615
NOI	18,578	20,684	59,042	61,498
Gross real estate	994,486	988,952	994,486	988,952
Operating Segments | Established | Northern California
Segment Reporting
Total revenue	95,234	103,511	300,856	307,207
NOI	69,752	79,076	228,047	235,884
Gross real estate	3,274,052	3,258,942	3,274,052	3,258,942
Operating Segments | Established | Southern California
Segment Reporting
Total revenue	105,964	113,202	327,865	337,488
NOI	71,125	79,357	228,181	239,452
Gross real estate	4,152,209	4,119,312	4,152,209	4,119,312
Operating Segments | Established | Expansion Markets [Member]
Segment Reporting
Total revenue	5,633	5,825	17,424	17,607
NOI	3,015	3,261	10,004	10,177
Gross real estate	320,944	320,114	320,944	320,114
Operating Segments | Other Stabilized
Segment Reporting
Total revenue	35,080	30,199	105,246	77,749
NOI	22,834	20,125	69,438	52,091
Gross real estate	1,595,739	1,404,506	1,595,739	1,404,506
Operating Segments | Development / Redevelopment
Segment Reporting
Total revenue	21,300	8,352	58,403	15,820
NOI	11,902	4,806	34,626	8,255
Gross real estate	2,569,413	1,824,012	2,569,413	1,824,012
Operating Segments | Disposals [Member]
Segment Reporting
Gross real estate		131,790		131,790
Land Held for Future Development
Segment Reporting
Gross real estate	43,494	20,095	43,494	20,095
Non-allocated
Segment Reporting
Total revenue	1,017	1,231	2,950	3,484
Gross real estate	407,821	552,179	407,821	552,179
Continuing Operations
Segment Reporting
Total revenue	565,955	581,519	1,739,300	1,702,944
Continuing Operations | Operating Segments | Established
Segment Reporting
Total revenue	508,558	541,737	1,572,701	1,605,891
Continuing Operations | Operating Segments | Other Stabilized
Segment Reporting
Total revenue	35,080	30,199	105,246	77,749
Continuing Operations | Non-allocated
Segment Reporting
Total revenue	$ 1,017	$ 1,231	$ 2,950	$ 3,484