Reportable Segments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Reconciliation of NOI
Rental income	$ 2,736,578	$ 2,605,311	$ 2,378,004
Property and maintenance expense	(479,160)	(473,098)	(449,427)
Real estate taxes and insurance expense	(339,802)	(325,401)	(293,999)
Property management expense	(81,185)	(79,636)	(84,342)
Total operating expenses	(900,147)	(878,135)	(827,768)
Rental income:
Rental Income - same store	2,566,705	2,441,390	2,374,350
Rental Income - non-same store	169,873	163,921	96,077
Rental Income	2,736,578	2,605,311	2,378,004
Operating expenses:
Operating Expenses - same store	837,880	817,337	815,865
Operating Expenses - non-same store	62,267	60,798	48,632
Operating Expenses	900,147	878,135	827,768
NOI:
NOI - same store	1,728,825	1,624,053	1,558,485
NOI - non-same store	107,606	103,123	47,445
NOI	$ 1,836,431	$ 1,727,176	1,550,236
Units in same store properties	96,286	97,911
Total Assets	$ 23,157,328	$ 22,950,614
Capital Expenditures	182,113	185,957
Same store (1)
NOI:
Total Assets	18,970,703	19,431,953
Capital Expenditures	173,414	178,960
Non-same store/other (2) (3)
NOI:
Total Assets	4,186,625	3,518,661
Capital Expenditures	8,699	6,997
Archstone pre-ownership (4)
Rental income:
Rental Income	0	0	(92,423)
Operating expenses:
Operating Expenses	0	0	(36,729)
NOI:
NOI	0	$ 0	(55,694)
Archstone Transaction [Member]
NOI:
Units in same store properties		18,465
Boston | Same store (1)
Rental income:
Rental Income - same store	252,620	$ 244,612	244,370
Operating expenses:
Operating Expenses - same store	81,176	77,408	78,249
NOI:
NOI - same store	171,444	167,204	166,121
Total Assets	1,840,812	1,897,740
Capital Expenditures	18,759	19,254
Boston | Non-same store/other (2) (3)
Rental income:
Rental Income - non-same store	9,028	3,637	2,728
Operating expenses:
Operating Expenses - non-same store	2,570	841	651
NOI:
NOI - non-same store	6,458	2,796	2,077
Total Assets	171,832	48,323
Capital Expenditures	629	699
New York | Same store (1)
Rental income:
Rental Income - same store	474,850	455,598	438,366
Operating expenses:
Operating Expenses - same store	176,654	170,549	165,329
NOI:
NOI - same store	298,196	285,049	273,037
Total Assets	4,585,328	4,647,269
Capital Expenditures	19,273	22,118
New York | Non-same store/other (2) (3)
Rental income:
Rental Income - non-same store	9,835	42	0
Operating expenses:
Operating Expenses - non-same store	7,460	92	0
NOI:
NOI - non-same store	2,375	(50)	0
Total Assets	364,475	356,064
Capital Expenditures	(8)	12
San Francisco | Same store (1)
Rental income:
Rental Income - same store	376,073	340,252	312,345
Operating expenses:
Operating Expenses - same store	108,003	106,425	108,218
NOI:
NOI - same store	268,070	233,827	204,127
Total Assets	2,653,629	2,718,174
Capital Expenditures	25,813	26,994
San Francisco | Non-same store/other (2) (3)
Rental income:
Rental Income - non-same store	6,408	15	0
Operating expenses:
Operating Expenses - non-same store	2,974	147	0
NOI:
NOI - non-same store	3,434	(132)	0
Total Assets	262,851	218,415
Capital Expenditures	6	0
Seattle | Same store (1)
Rental income:
Rental Income - same store	164,319	153,197	146,109
Operating expenses:
Operating Expenses - same store	50,079	50,377	49,169
NOI:
NOI - same store	114,240	102,820	96,940
Total Assets	1,058,090	1,087,575
Capital Expenditures	13,565	14,333
Seattle | Non-same store/other (2) (3)
Rental income:
Rental Income - non-same store	22,199	6,951	4,387
Operating expenses:
Operating Expenses - non-same store	6,478	2,172	1,336
NOI:
NOI - non-same store	15,721	4,779	3,051
Total Assets	453,111	335,086
Capital Expenditures	457	918
Southern California | Same store (1)
Rental income:
Rental Income - same store	433,431	410,094	401,516
Operating expenses:
Operating Expenses - same store	136,559	135,091	137,667
NOI:
NOI - same store	296,872	275,003	263,849
Total Assets	2,725,230	2,809,390
Capital Expenditures	29,729	26,713
Southern California | Non-same store/other (2) (3)
Rental income:
Rental Income - non-same store	71,719	49,663	15,016
Operating expenses:
Operating Expenses - non-same store	26,264	19,518	6,846
NOI:
NOI - non-same store	45,455	30,145	8,170
Total Assets	911,728	851,812
Capital Expenditures	6,360	1,968
Washington D.C. | Same store (1)
Rental income:
Rental Income - same store	455,341	451,973	448,520
Operating expenses:
Operating Expenses - same store	149,190	145,523	140,708
NOI:
NOI - same store	306,151	306,450	307,812
Total Assets	4,169,317	4,282,317
Capital Expenditures	35,522	44,607
Washington D.C. | Non-same store/other (2) (3)
Rental income:
Rental Income - non-same store	21,822	17,927	13,562
Operating expenses:
Operating Expenses - non-same store	6,313	6,115	4,086
NOI:
NOI - non-same store	15,509	11,812	9,476
Total Assets	235,841	243,174
Capital Expenditures	677	467
Non-core – South Florida | Same store (1)
Rental income:
Rental Income - same store	202,714	191,729	182,620
Operating expenses:
Operating Expenses - same store	72,792	70,295	69,475
NOI:
NOI - same store	129,922	121,434	113,145
Total Assets	1,109,699	1,135,553
Capital Expenditures	16,297	14,335
Non-core – South Florida | Non-same store/other (2) (3)
Rental income:
Rental Income - non-same store	7,912	5,480	390
Operating expenses:
Operating Expenses - non-same store	2,830	2,619	810
NOI:
NOI - non-same store	5,082	2,861	(420)
Total Assets	64,854	67,834
Capital Expenditures	42	8
Non-core – Denver | Same store (1)
Rental income:
Rental Income - same store	120,938	111,190	103,124
Operating expenses:
Operating Expenses - same store	31,708	30,811	30,567
NOI:
NOI - same store	89,230	80,379	72,557
Total Assets	506,317	520,537
Capital Expenditures	8,341	5,863
Non-core – other | Same store (1)
Rental income:
Rental Income - same store	86,419	82,745	97,380
Operating expenses:
Operating Expenses - same store	31,719	30,858	36,483
NOI:
NOI - same store	54,700	51,887	60,897
Total Assets	322,281	333,398
Capital Expenditures	6,115	4,743
Other (3) | Non-same store/other (2) (3)
Rental income:
Rental Income - non-same store	20,950	80,206	59,994
Operating expenses:
Operating Expenses - non-same store	7,378	29,294	34,903
NOI:
NOI - non-same store	13,572	50,912	$ 25,091
Total Assets	1,721,933	1,397,953
Capital Expenditures	$ 536	$ 2,925