Reportable Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Reportable Segments - Reconciliation of NOI
Rental income	$ 594,939	$ 676,508	$ 1,211,104	$ 1,341,114
Property and maintenance expense	(96,307)	(118,005)	(205,472)	(242,565)
Real estate taxes and insurance expense	(77,415)	(83,119)	(157,611)	(169,551)
Total operating expenses	(173,722)	(201,124)	(363,083)	(412,116)
Net operating income	421,217	475,384	848,021	928,998
Rental income:
Rental Income - Same Store	556,022	533,482	1,099,117	1,053,117
Rental Income - Non-same store/other	38,917	143,026	111,987	287,997
Rental Income	594,939	676,508	1,211,104	1,341,114
Operating expenses:
Operating Expenses - Same Store	159,569	156,886	320,884	318,166
Operating Expenses - Non-same store/other	14,153	44,238	42,199	93,950
Operating expenses	173,722	201,124	363,083	412,116
NOI:
Net operating income - Same Store	396,453	376,596	778,233	734,951
Net operating income - Non-same store/other	24,764	98,788	69,788	194,047
Net operating income	421,217	475,384	848,021	928,998
Total Assets	$ 21,229,922		21,229,922		$ 23,110,196
Capital Expenditures			$ 74,450
Units in same store properties	72,781		72,494
Same Store [Member]
NOI:
Total Assets	$ 16,990,824		$ 16,990,824
Capital Expenditures			64,882
Non-same store [Member]
NOI:
Total Assets	4,239,098		4,239,098
Capital Expenditures			9,568
Los Angeles [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	91,699	86,515	181,849	171,169
Operating expenses:
Operating Expenses - Same Store	26,489	25,893	52,847	52,082
NOI:
Net operating income - Same Store	65,210	60,622	129,002	119,087
Total Assets	2,550,146		2,550,146
Capital Expenditures			11,718
Los Angeles [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	9,198	6,505	16,460	13,825
Operating expenses:
Operating Expenses - Non-same store/other	3,021	2,382	5,726	4,766
NOI:
Net operating income - Non-same store/other	6,177	4,123	10,734	9,059
Total Assets	455,857		455,857
Capital Expenditures			5,803
San Diego [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	21,877	20,643	43,306	40,874
Operating expenses:
Operating Expenses - Same Store	5,861	5,756	11,696	11,417
NOI:
Net operating income - Same Store	16,016	14,887	31,610	29,457
Total Assets	480,150		480,150
Capital Expenditures			2,465
Orange County [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	19,802	18,601	39,116	36,922
Operating expenses:
Operating Expenses - Same Store	4,599	4,639	9,332	9,327
NOI:
Net operating income - Same Store	15,203	13,962	29,784	27,595
Total Assets	265,300		265,300
Capital Expenditures			3,741
Orange County [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	1,201	0	2,358	0
Operating expenses:
Operating Expenses - Non-same store/other	350	0	685	0
NOI:
Net operating income - Non-same store/other	851	0	1,673	0
Total Assets	76,337		76,337
Capital Expenditures			26
Southern California [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	133,378	125,759	264,271	248,965
Operating expenses:
Operating Expenses - Same Store	36,949	36,288	73,875	72,826
NOI:
Net operating income - Same Store	96,429	89,471	190,396	176,139
Total Assets	3,295,596		3,295,596
Capital Expenditures			17,924
Southern California [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	10,399	6,505	18,818	13,825
Operating expenses:
Operating Expenses - Non-same store/other	3,371	2,382	6,411	4,766
NOI:
Net operating income - Non-same store/other	7,028	4,123	12,407	9,059
Total Assets	532,194		532,194
Capital Expenditures			5,829
New York [Domain] | Same Store [Member]
Rental income:
Rental Income - Same Store	114,532	111,885	227,736	222,210
Operating expenses:
Operating Expenses - Same Store	38,487	37,716	78,629	77,223
NOI:
Net operating income - Same Store	76,045	74,169	149,107	144,987
Total Assets	4,314,790		4,314,790
Capital Expenditures			9,838
New York [Domain] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	8,628	1,006	15,714	1,291
Operating expenses:
Operating Expenses - Non-same store/other	3,898	1,021	7,533	1,453
NOI:
Net operating income - Non-same store/other	4,730	(15)	8,181	(162)
Total Assets	436,213		436,213
Capital Expenditures			33
Washington DC [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	106,148	104,907	210,416	208,247
Operating expenses:
Operating Expenses - Same Store	30,871	30,609	62,296	62,646
NOI:
Net operating income - Same Store	75,277	74,298	148,120	145,601
Total Assets	3,965,195		3,965,195
Capital Expenditures			13,191
Washington DC [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	859	1,017	1,818	2,062
Operating expenses:
Operating Expenses - Non-same store/other	166	183	346	380
NOI:
Net operating income - Non-same store/other	693	834	1,472	1,682
Total Assets	45,869		45,869
Capital Expenditures			308
San Francisco [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	91,811	85,224	182,485	168,047
Operating expenses:
Operating Expenses - Same Store	22,230	21,390	44,428	42,909
NOI:
Net operating income - Same Store	69,581	63,834	138,057	125,138
Total Assets	2,501,535		2,501,535
Capital Expenditures			10,250
San Francisco [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	8,043	524	13,328	640
Operating expenses:
Operating Expenses - Non-same store/other	2,647	394	4,710	615
NOI:
Net operating income - Non-same store/other	5,396	130	8,618	25
Total Assets	951,966		951,966
Capital Expenditures			261
Boston [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	62,272	60,467	123,890	120,294
Operating expenses:
Operating Expenses - Same Store	16,848	17,470	34,272	36,320
NOI:
Net operating income - Same Store	45,424	42,997	89,618	83,974
Total Assets	1,789,339		1,789,339
Capital Expenditures			8,285
Boston [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	2,909	2,433	5,542	3,375
Operating expenses:
Operating Expenses - Non-same store/other	698	580	1,415	782
NOI:
Net operating income - Non-same store/other	2,211	1,853	4,127	2,593
Total Assets	169,544		169,544
Capital Expenditures			357
Seattle | Same Store [Member]
Rental income:
Rental Income - Same Store	40,401	38,103	75,565	71,250
Operating expenses:
Operating Expenses - Same Store	11,344	10,564	21,392	19,868
NOI:
Net operating income - Same Store	29,057	27,539	54,173	51,382
Total Assets	1,045,598		1,045,598
Capital Expenditures			4,800
Seattle | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	4,827	68	12,584	4,003
Operating expenses:
Operating Expenses - Non-same store/other	1,164	88	3,035	1,090
NOI:
Net operating income - Non-same store/other	3,663	(20)	9,549	2,913
Total Assets	331,810		331,810
Capital Expenditures			432
All Other Markets | Same Store [Member]
Rental income:
Rental Income - Same Store	7,480	7,137	14,754	14,104
Operating expenses:
Operating Expenses - Same Store	2,840	2,849	5,992	6,374
NOI:
Net operating income - Same Store	4,640	4,288	8,762	7,730
Total Assets	78,771		78,771
Capital Expenditures			594
Other [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	3,252	131,473	44,183	262,801
Operating expenses:
Operating Expenses - Non-same store/other	2,209	39,590	18,749	84,864
NOI:
Net operating income - Non-same store/other	1,043	$ 91,883	25,434	$ 177,937
Total Assets	$ 1,771,502		1,771,502
Capital Expenditures			$ 2,348