Segment Reporting (Details 3) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting
Total revenue	$ 576,405	$ 577,263	$ 1,178,056	$ 1,143,446
NOI	401,373	400,095	825,908	795,011
Gross real estate	23,789,801	22,632,709	23,789,801	22,632,709
Operating Segments | Established
Segment Reporting
Total revenue	523,531	539,505	1,071,487	1,071,335
NOI	368,191	382,416	759,836	762,753
Gross real estate	19,394,119	19,228,408	19,394,119	19,228,408
Operating Segments | Established | New England
Segment Reporting
Total revenue	79,729	79,566	161,398	158,254
NOI	52,835	52,474	106,515	104,557
Gross real estate	2,768,509	2,728,480	2,768,509	2,728,480
Operating Segments | Established | Metro NY/NJ
Segment Reporting
Total revenue	113,942	120,427	234,673	238,804
NOI	78,080	84,420	162,564	167,404
Gross real estate	4,339,998	4,316,859	4,339,998	4,316,859
Operating Segments | Established | Mid-Atlantic
Segment Reporting
Total revenue	87,970	90,115	179,687	178,486
NOI	61,644	63,241	127,953	126,157
Gross real estate	3,552,832	3,517,332	3,552,832	3,517,332
Operating Segments | Established | Pacific Northwest
Segment Reporting
Total revenue	27,678	28,224	56,414	56,026
NOI	19,626	20,605	40,464	40,815
Gross real estate	992,976	987,121	992,976	987,121
Operating Segments | Established | Northern California
Segment Reporting
Total revenue	101,263	102,435	205,623	203,695
NOI	77,844	78,093	158,295	156,808
Gross real estate	3,271,293	3,252,502	3,271,293	3,252,502
Operating Segments | Established | Southern California
Segment Reporting
Total revenue	107,091	112,821	221,901	224,287
NOI	74,601	80,180	157,056	160,096
Gross real estate	4,147,828	4,106,419	4,147,828	4,106,419
Operating Segments | Established | Expansion Markets [Member]
Segment Reporting
Total revenue	5,858	5,917	11,791	11,783
NOI	3,561	3,403	6,989	6,916
Gross real estate	320,683	319,695	320,683	319,695
Operating Segments | Other Stabilized
Segment Reporting
Total revenue	34,677	25,522	70,167	47,548
NOI	23,108	17,237	46,604	31,966
Gross real estate	1,593,551	1,257,613	1,593,551	1,257,613
Operating Segments | Development / Redevelopment
Segment Reporting
Total revenue	16,692	2,410	32,465	2,959
NOI	10,074	442	19,468	292
Gross real estate	2,346,168	1,589,009	2,346,168	1,589,009
Operating Segments | Disposals [Member]
Segment Reporting
Gross real estate		209,170		209,170
Land Held for Future Development
Segment Reporting
Gross real estate	39,829	18,606	39,829	18,606
Non-allocated
Segment Reporting
Total revenue	926	1,114	1,933	2,252
Gross real estate	416,134	539,073	416,134	539,073
Continuing Operations
Segment Reporting
Total revenue	575,826	568,551	1,176,052	1,124,094
Continuing Operations | Operating Segments | Established
Segment Reporting
Total revenue	523,531	539,505	1,071,487	1,071,335
Continuing Operations | Operating Segments | Other Stabilized
Segment Reporting
Total revenue	34,677	25,522	70,167	47,548
Continuing Operations | Non-allocated
Segment Reporting
Total revenue	$ 926	$ 1,114	$ 1,933	$ 2,252