Segment Reporting (Details 3) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting
Total revenue	$ 550,500	$ 516,211	$ 1,603,337	$ 1,527,015
NOI	$ 378,591	$ 345,196	$ 1,102,939	$ 1,030,515
% NOI change from prior year	9.70%	20.20%	7.00%	37.30%
Gross real estate	$ 21,492,926	$ 20,362,663	$ 21,492,926	$ 20,362,663
Gross real estate assets held for sale	53,723	135,054	53,723	135,054
Avalon Maplewood
Segment Reporting
Gain on business interruption insurance recovery	3,495		3,495
Avalon at Edgewater
Segment Reporting
Gain on business interruption insurance recovery				20,306
Operating Segments | Established
Segment Reporting
Total revenue	398,349	382,410	1,180,695	1,129,072
NOI	$ 279,037	$ 267,219	$ 831,400	$ 792,340
% NOI change from prior year	2.10%	4.40%	2.70%	4.40%
Gross real estate	$ 13,458,526	$ 13,448,763	$ 13,458,526	$ 13,448,763
Operating Segments | Established | New England
Segment Reporting
Total revenue	58,941	59,321	174,348	174,731
NOI	$ 38,055	$ 37,657	$ 111,931	$ 111,497
% NOI change from prior year	3.00%	0.60%	2.60%	5.90%
Gross real estate	$ 1,846,937	$ 1,845,679	$ 1,846,937	$ 1,845,679
Operating Segments | Established | Metro NY/NJ
Segment Reporting
Total revenue	91,699	91,181	271,262	268,781
NOI	$ 61,932	$ 61,905	$ 184,434	$ 183,155
% NOI change from prior year	1.60%	1.20%	2.00%	1.80%
Gross real estate	$ 2,969,873	$ 3,206,696	$ 2,969,873	$ 3,206,696
Operating Segments | Established | Mid-Atlantic
Segment Reporting
Total revenue	56,321	58,928	168,098	174,922
NOI	$ 38,782	$ 40,029	$ 116,272	$ 120,623
% NOI change from prior year	1.80%	0.40%	1.80%	1.40%
Gross real estate	$ 2,069,486	$ 2,335,116	$ 2,069,486	$ 2,335,116
Operating Segments | Established | Pacific Northwest
Segment Reporting
Total revenue	21,528	18,627	62,773	54,085
NOI	$ 15,687	$ 13,541	$ 45,519	$ 39,165
% NOI change from prior year	5.10%	12.10%	5.40%	8.10%
Gross real estate	$ 734,407	$ 736,377	$ 734,407	$ 736,377
Operating Segments | Established | Northern California
Segment Reporting
Total revenue	84,634	80,783	251,985	238,867
NOI	$ 64,557	$ 61,560	$ 192,861	$ 182,658
% NOI change from prior year	1.30%	5.90%	1.90%	8.00%
Gross real estate	$ 2,824,608	$ 2,657,020	$ 2,824,608	$ 2,657,020
Operating Segments | Established | Southern California
Segment Reporting
Total revenue	85,226	73,570	252,229	217,686
NOI	$ 60,024	$ 52,527	$ 180,383	$ 155,242
% NOI change from prior year	2.30%	11.10%	4.30%	10.30%
Gross real estate	$ 3,013,215	$ 2,667,875	$ 3,013,215	$ 2,667,875
Operating Segments | Other Stabilized
Segment Reporting
Total revenue	71,150	52,971	208,729	175,186
NOI	49,177	34,653	146,242	125,027
Gross real estate	3,086,022	2,325,539	3,086,022	2,325,539
Operating Segments | Development / Redevelopment
Segment Reporting
Total revenue	76,964	63,122	195,041	164,865
NOI	50,377	43,324	125,297	113,148
Gross real estate	4,766,894	3,994,361	4,766,894	3,994,361
Land Held for Future Development
Segment Reporting
Gross real estate	85,863	519,626	85,863	519,626
Non-allocated
Segment Reporting
Total revenue	993	1,320	3,290	4,310
Gross real estate	95,621	74,374	95,621	74,374
Continuing Operations
Segment Reporting
Total revenue	$ 547,456	$ 499,823	$ 1,587,755	$ 1,473,433