Reportable Segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Reportable Segments - Reconciliation of NOI
Rental income	$ 605,856	$ 694,245	$ 1,816,960	$ 2,035,359
Property and maintenance expense	(104,216)	(122,383)	(309,688)	(364,948)
Real estate taxes and insurance expense	(81,343)	(84,962)	(238,954)	(254,513)
Total operating expenses	(185,559)	(207,345)	(548,642)	(619,461)
Net operating income	420,297	486,900	1,268,318	1,415,898
Rental income:
Rental Income - Same Store	563,892	545,281	1,647,480	1,583,810
Rental Income - Non-same store/other	41,964	148,964	169,480	451,549
Rental Income	605,856	694,245	1,816,960	2,035,359
Operating expenses:
Operating Expenses - Same Store	168,706	159,343	484,643	472,930
Operating Expenses - Non-same store/other	16,853	48,002	63,999	146,531
Operating expenses	185,559	207,345	548,642	619,461
NOI:
Net operating income - Same Store	395,186	385,938	1,162,837	1,110,880
Net operating income - Non-same store/other	25,111	100,962	105,481	305,018
Net operating income	420,297	486,900	1,268,318	1,415,898
Total Assets	$ 21,297,744		21,297,744		$ 23,110,196
Capital Expenditures			$ 124,551
Units in same store properties	72,229		71,488
Same Store [Member]
NOI:
Total Assets	$ 16,843,186		$ 16,843,186
Capital Expenditures			112,514
Non-same store [Member]
NOI:
Total Assets	4,454,558		4,454,558
Capital Expenditures			12,037
Los Angeles [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	95,928	91,212	275,157	259,974
Operating expenses:
Operating Expenses - Same Store	28,365	27,296	80,489	78,781
NOI:
Net operating income - Same Store	67,563	63,916	194,668	181,193
Total Assets	2,532,524		2,532,524
Capital Expenditures			19,939
Los Angeles [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	7,659	4,470	26,766	20,708
Operating expenses:
Operating Expenses - Non-same store/other	3,285	1,817	10,085	7,230
NOI:
Net operating income - Non-same store/other	4,374	2,653	16,681	13,478
Total Assets	682,199		682,199
Capital Expenditures			7,151
San Diego [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	22,393	21,327	65,699	62,201
Operating expenses:
Operating Expenses - Same Store	6,025	5,894	17,721	17,311
NOI:
Net operating income - Same Store	16,368	15,433	47,978	44,890
Total Assets	476,349		476,349
Capital Expenditures			4,259
Orange County [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	20,173	19,047	59,289	55,969
Operating expenses:
Operating Expenses - Same Store	4,920	4,824	14,251	14,151
NOI:
Net operating income - Same Store	15,253	14,223	45,038	41,818
Total Assets	263,634		263,634
Capital Expenditures			5,930
Orange County [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	1,265	0	3,623	0
Operating expenses:
Operating Expenses - Non-same store/other	588	0	1,273	0
NOI:
Net operating income - Non-same store/other	677	0	2,350	0
Total Assets	75,839		75,839
Capital Expenditures			123
Southern California [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	138,494	131,586	400,145	378,144
Operating expenses:
Operating Expenses - Same Store	39,310	38,014	112,461	110,243
NOI:
Net operating income - Same Store	99,184	93,572	287,684	267,901
Total Assets	3,272,507		3,272,507
Capital Expenditures			30,128
Southern California [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	8,924	4,470	30,389	20,708
Operating expenses:
Operating Expenses - Non-same store/other	3,873	1,817	11,358	7,230
NOI:
Net operating income - Non-same store/other	5,051	2,653	19,031	13,478
Total Assets	758,038		758,038
Capital Expenditures			7,274
New York [Domain] | Same Store [Member]
Rental income:
Rental Income - Same Store	115,652	114,112	343,388	336,321
Operating expenses:
Operating Expenses - Same Store	42,209	37,639	120,838	115,507
NOI:
Net operating income - Same Store	73,443	76,473	222,550	220,814
Total Assets	4,309,221		4,309,221
Capital Expenditures			16,661
New York [Domain] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	8,873	3,142	24,587	4,424
Operating expenses:
Operating Expenses - Non-same store/other	3,365	2,137	10,858	3,590
NOI:
Net operating income - Non-same store/other	5,508	1,005	13,729	834
Total Assets	438,413		438,413
Capital Expenditures			80
Washington DC [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	107,168	105,526	317,584	313,773
Operating expenses:
Operating Expenses - Same Store	32,891	31,740	95,187	94,386
NOI:
Net operating income - Same Store	74,277	73,786	222,397	219,387
Total Assets	3,948,781		3,948,781
Capital Expenditures			24,680
Washington DC [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	822	1,088	2,640	3,147
Operating expenses:
Operating Expenses - Non-same store/other	177	174	541	555
NOI:
Net operating income - Non-same store/other	645	914	2,099	2,592
Total Assets	46,180		46,180
Capital Expenditures			826
San Francisco [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	92,101	87,678	272,729	254,032
Operating expenses:
Operating Expenses - Same Store	22,785	21,590	66,596	63,898
NOI:
Net operating income - Same Store	69,316	66,088	206,133	190,134
Total Assets	2,456,465		2,456,465
Capital Expenditures			17,300
San Francisco [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	12,601	2,887	26,974	4,489
Operating expenses:
Operating Expenses - Non-same store/other	4,869	1,044	10,303	2,006
NOI:
Net operating income - Non-same store/other	7,732	1,843	16,671	2,483
Total Assets	973,068		973,068
Capital Expenditures			140
Boston [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	63,824	62,662	184,376	179,714
Operating expenses:
Operating Expenses - Same Store	18,297	17,825	51,561	52,941
NOI:
Net operating income - Same Store	45,527	44,837	132,815	126,773
Total Assets	1,764,497		1,764,497
Capital Expenditures			13,906
Boston [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	899	1,003	8,310	6,264
Operating expenses:
Operating Expenses - Non-same store/other	189	217	2,073	1,611
NOI:
Net operating income - Non-same store/other	710	786	6,237	4,653
Total Assets	168,224		168,224
Capital Expenditures			403
Seattle | Same Store [Member]
Rental income:
Rental Income - Same Store	41,836	39,195	115,072	108,391
Operating expenses:
Operating Expenses - Same Store	11,281	10,480	32,118	29,759
NOI:
Net operating income - Same Store	30,555	28,715	82,954	78,632
Total Assets	1,038,137		1,038,137
Capital Expenditures			9,114
Seattle | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	5,251	533	20,170	6,609
Operating expenses:
Operating Expenses - Non-same store/other	1,106	243	4,785	1,924
NOI:
Net operating income - Non-same store/other	4,145	290	15,385	4,685
Total Assets	329,230		329,230
Capital Expenditures			542
All Other Markets | Same Store [Member]
Rental income:
Rental Income - Same Store	4,817	4,522	14,186	13,435
Operating expenses:
Operating Expenses - Same Store	1,933	2,055	5,882	6,196
NOI:
Net operating income - Same Store	2,884	2,467	8,304	7,239
Total Assets	53,578		53,578
Capital Expenditures			725
Other [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	4,594	135,841	56,410	405,908
Operating expenses:
Operating Expenses - Non-same store/other	3,274	42,370	24,081	129,615
NOI:
Net operating income - Non-same store/other	1,320	$ 93,471	32,329	$ 276,293
Total Assets	$ 1,741,405		1,741,405
Capital Expenditures			$ 2,772