Reportable Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Reportable Segments
Assets	$ 23,008,094		$ 23,008,094		$ 22,834,545
Payments to Acquire Other Property, Plant, and Equipment			133,181
Rental income:
Same store	635,853	610,610	1,864,729	1,792,122
Segment Reporting Segment Non Same Store Rental Income	26,148	13,453	77,763	41,470
Segment Reporting Information Revenues	662,001	624,063	1,942,492	1,741,169
Operating expenses:
Same store	211,344	210,081	634,076	623,298
Segment Reporting Segment Non Same Store Operating Expenses	7,775	3,492	33,826	25,391
Segment Reporting Segment Operating Expenses	219,119	213,573	667,902	611,960
NOI:
Same store	424,509	400,529	1,230,653	1,168,824
Segment Reporting Information Non Same Store Net Operating Income	18,373	9,961	43,937	16,079
Segment Reporting Information Net Operating Income	442,882	410,490	1,274,590	1,129,209
Reportable Segments (Textuals) [Abstract]
Units in same store properties	100,196		99,686
Rental income	662,001	624,063	1,942,492	1,741,169
Property Repairs and Maintenance	(120,144)	(118,782)	(361,105)	(330,812)
Real Estate Taxes and Insurance	(80,568)	(75,916)	(245,717)	(217,753)
Property management	(18,407)	(18,875)	(61,080)	(63,395)
Total Operating Expenses	(219,119)	(213,573)	(667,902)	(611,960)
Archstone [Member]
Reportable Segments (Textuals) [Abstract]
Units in same store properties			18,465
Same Store [Domain]
Reportable Segments
Assets	19,851,704		19,851,704
Payments to Acquire Other Property, Plant, and Equipment			129,237
Non-same store [Domain]
Reportable Segments
Assets	3,156,390		3,156,390
Payments to Acquire Other Property, Plant, and Equipment			3,944
Boston [Domain]
Rental income:
Same store	63,485	61,687	188,509	182,143
Segment Reporting Segment Non Same Store Rental Income	931	747	2,749	1,900
Operating expenses:
Same store	19,781	19,721	61,195	59,373
Segment Reporting Segment Non Same Store Operating Expenses	215	176	639	430
NOI:
Same store	43,704	41,966	127,314	122,770
Segment Reporting Information Non Same Store Net Operating Income	716	571	2,110	1,470
Boston [Domain] | Same Store [Domain]
Reportable Segments
Assets	1,939,055		1,939,055
Payments to Acquire Other Property, Plant, and Equipment			14,656
Boston [Domain] | Non-same store [Domain]
Reportable Segments
Assets	48,570		48,570
Payments to Acquire Other Property, Plant, and Equipment			690
Denver [Domain]
Rental income:
Same store	28,269	26,303	82,392	76,796
Operating expenses:
Same store	8,164	8,109	23,263	23,095
NOI:
Same store	20,105	18,194	59,129	53,701
Denver [Domain] | Same Store [Domain]
Reportable Segments
Assets	525,685		525,685
Payments to Acquire Other Property, Plant, and Equipment			3,900
New York [Domain]
Rental income:
Same store	114,968	110,588	340,374	327,884
Operating expenses:
Same store	41,457	41,215	129,561	124,960
NOI:
Same store	73,511	69,373	210,813	202,924
New York [Domain] | Same Store [Domain]
Reportable Segments
Assets	4,683,104		4,683,104
Payments to Acquire Other Property, Plant, and Equipment			14,802
San Francisco [Domain]
Rental income:
Same store	86,468	79,602	251,812	232,062
Operating expenses:
Same store	26,938	27,312	79,898	81,417
NOI:
Same store	59,530	52,290	171,914	150,645
San Francisco [Domain] | Same Store [Domain]
Reportable Segments
Assets	2,736,460		2,736,460
Payments to Acquire Other Property, Plant, and Equipment			20,234
Seattle [Domain]
Rental income:
Same store	41,575	38,786	116,581	108,789
Segment Reporting Segment Non Same Store Rental Income	2,464	0	8,608	2,855
Operating expenses:
Same store	13,428	12,992	38,649	37,108
Segment Reporting Segment Non Same Store Operating Expenses	645	0	3,014	813
NOI:
Same store	28,147	25,794	77,932	71,681
Segment Reporting Information Non Same Store Net Operating Income	1,819	0	5,594	2,042
Seattle [Domain] | Same Store [Domain]
Reportable Segments
Assets	1,039,100		1,039,100
Payments to Acquire Other Property, Plant, and Equipment			9,699
Seattle [Domain] | Non-same store [Domain]
Reportable Segments
Assets	226,023		226,023
Payments to Acquire Other Property, Plant, and Equipment			396
South Florida [Domain]
Rental income:
Same store	48,245	46,135	143,000	136,599
Segment Reporting Segment Non Same Store Rental Income	1,645	21	3,687	44
Operating expenses:
Same store	17,805	17,673	53,347	52,238
Segment Reporting Segment Non Same Store Operating Expenses	736	218	2,113	364
NOI:
Same store	30,440	28,462	89,653	84,361
Segment Reporting Information Non Same Store Net Operating Income	909	(197)	1,574	(320)
South Florida [Domain] | Same Store [Domain]
Reportable Segments
Assets	1,145,788		1,145,788
Payments to Acquire Other Property, Plant, and Equipment			11,377
South Florida [Domain] | Non-same store [Domain]
Reportable Segments
Assets	68,528		68,528
Payments to Acquire Other Property, Plant, and Equipment			0
Southern California [Domain]
Rental income:
Same store	106,974	102,422	314,247	300,788
Segment Reporting Segment Non Same Store Rental Income	11,889	4,413	28,005	9,824
Operating expenses:
Same store	35,543	35,062	104,996	104,211
Segment Reporting Segment Non Same Store Operating Expenses	4,653	1,962	12,737	4,554
NOI:
Same store	71,431	67,360	209,251	196,577
Segment Reporting Information Non Same Store Net Operating Income	7,236	2,451	15,268	5,270
Southern California [Domain] | Same Store [Domain]
Reportable Segments
Assets	2,955,062		2,955,062
Payments to Acquire Other Property, Plant, and Equipment			19,125
Southern California [Domain] | Non-same store [Domain]
Reportable Segments
Assets	754,384		754,384
Payments to Acquire Other Property, Plant, and Equipment			971
Washington DC [Domain]
Rental income:
Same store	114,478	114,793	335,154	337,270
Segment Reporting Segment Non Same Store Rental Income	4,899	2,458	17,324	9,109
Operating expenses:
Same store	36,841	36,905	108,931	107,547
Segment Reporting Segment Non Same Store Operating Expenses	1,654	1,003	6,005	3,276
NOI:
Same store	77,637	77,888	226,223	229,723
Segment Reporting Information Non Same Store Net Operating Income	3,245	1,455	11,319	5,833
Washington DC [Domain] | Same Store [Domain]
Reportable Segments
Assets	4,252,450		4,252,450
Payments to Acquire Other Property, Plant, and Equipment			30,477
Washington DC [Domain] | Non-same store [Domain]
Reportable Segments
Assets	303,871		303,871
Payments to Acquire Other Property, Plant, and Equipment			1,290
Non-Core [Domain]
Rental income:
Same store	31,391	30,294	92,660	89,791
Operating expenses:
Same store	11,387	11,092	34,236	33,349
NOI:
Same store	20,004	19,202	58,424	56,442
Non-Core [Domain] | Same Store [Domain]
Reportable Segments
Assets	575,000		575,000
Payments to Acquire Other Property, Plant, and Equipment			4,967
Archstone pre-ownership [Member]
Rental income:
Same store			0	(92,423)
Operating expenses:
Same store			0	(36,729)
NOI:
Same store			0	(55,694)
Other [Domain]
Rental income:
Segment Reporting Segment Non Same Store Rental Income	4,320	5,814	17,390	17,738
Operating expenses:
Segment Reporting Segment Non Same Store Operating Expenses	(128)	133	9,318	15,954
NOI:
Segment Reporting Information Non Same Store Net Operating Income	4,448	5,681	8,072	1,784
Other [Domain] | Non-same store [Domain]
Reportable Segments
Assets	1,755,014		1,755,014
Payments to Acquire Other Property, Plant, and Equipment			$ 597