Reportable Segments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Reportable Segments - Reconciliation of NOI
Rental income	$ 616,165	$ 664,606
Property and maintenance expense	(109,165)	(124,560)
Real estate taxes and insurance expense	(80,196)	(86,432)
Total operating expenses	(189,361)	(210,992)
Net operating income	426,804	453,614
Rental income:
Rental Income - Same Store	547,676	523,739
Rental Income - Non-same store/other	68,489	140,867
Rental Income	616,165	664,606
Operating expenses:
Operating Expenses - Same Store	162,676	162,663
Operating Expenses - Non-same store/other	26,685	48,329
Operating expenses	189,361	210,992
NOI:
Net operating income - Same Store	385,000	361,076
Net operating income - Non-same store/other	41,804	92,538
Net operating income	426,804	453,614
Total Assets	21,301,292		$ 23,110,196
Capital Expenditures	$ 33,902
Units in same store properties	73,222
Los Angeles [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	$ 90,150	84,654
Operating expenses:
Operating Expenses - Same Store	26,359	26,189
NOI:
Net operating income - Same Store	63,791	58,465
Total Assets	2,567,837
Capital Expenditures	5,031
Los Angeles [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	7,264	7,339
Operating expenses:
Operating Expenses - Non-same store/other	2,573	2,384
NOI:
Net operating income - Non-same store/other	4,691	4,955
Total Assets	459,013
Capital Expenditures	3,164
San Diego [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	21,428	20,231
Operating expenses:
Operating Expenses - Same Store	5,835	5,661
NOI:
Net operating income - Same Store	15,593	14,570
Total Assets	483,643
Capital Expenditures	673
Orange County [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	19,314	18,321
Operating expenses:
Operating Expenses - Same Store	4,733	4,688
NOI:
Net operating income - Same Store	14,581	13,633
Total Assets	266,770
Capital Expenditures	1,738
Orange County [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	1,158	0
Operating expenses:
Operating Expenses - Non-same store/other	334	0
NOI:
Net operating income - Non-same store/other	824	0
Total Assets	77,324
Capital Expenditures	12
Southern California [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	130,892	123,206
Operating expenses:
Operating Expenses - Same Store	36,927	36,538
NOI:
Net operating income - Same Store	93,965	86,668
Total Assets	3,318,250
Capital Expenditures	7,442
Southern California [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	8,422	7,339
Operating expenses:
Operating Expenses - Non-same store/other	2,907	2,384
NOI:
Net operating income - Non-same store/other	5,515	4,955
Total Assets	536,337
Capital Expenditures	3,176
New York [Domain] | Same Store [Member]
Rental income:
Rental Income - Same Store	113,204	110,123
Operating expenses:
Operating Expenses - Same Store	40,141	39,507
NOI:
Net operating income - Same Store	73,063	70,616
Total Assets	4,348,318
Capital Expenditures	3,994
New York [Domain] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	7,086	292
Operating expenses:
Operating Expenses - Non-same store/other	3,625	432
NOI:
Net operating income - Non-same store/other	3,461	(140)
Total Assets	440,315
Capital Expenditures	19
Washington DC [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	104,268	103,340
Operating expenses:
Operating Expenses - Same Store	31,425	32,037
NOI:
Net operating income - Same Store	72,843	71,303
Total Assets	3,993,480
Capital Expenditures	5,556
Washington DC [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	959	1,047
Operating expenses:
Operating Expenses - Non-same store/other	170	197
NOI:
Net operating income - Non-same store/other	789	850
Total Assets	45,975
Capital Expenditures	0
San Francisco [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	90,674	82,784
Operating expenses:
Operating Expenses - Same Store	22,198	21,519
NOI:
Net operating income - Same Store	68,476	61,265
Total Assets	2,518,610
Capital Expenditures	4,891
San Francisco [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	4,298	83
Operating expenses:
Operating Expenses - Non-same store/other	1,550	221
NOI:
Net operating income - Non-same store/other	2,748	(138)
Total Assets	262,882
Capital Expenditures	0
Boston [Member] | Same Store [Member]
Rental income:
Rental Income - Same Store	62,325	60,512
Operating expenses:
Operating Expenses - Same Store	17,648	19,124
NOI:
Net operating income - Same Store	44,677	41,388
Total Assets	1,811,047
Capital Expenditures	3,626
Boston [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	2,634	946
Operating expenses:
Operating Expenses - Non-same store/other	710	202
NOI:
Net operating income - Non-same store/other	1,924	744
Total Assets	170,841
Capital Expenditures	294
Seattle | Same Store [Member]
Rental income:
Rental Income - Same Store	37,243	35,131
Operating expenses:
Operating Expenses - Same Store	10,572	9,807
NOI:
Net operating income - Same Store	26,671	25,324
Total Assets	1,053,316
Capital Expenditures	2,345
Seattle | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	5,679	1,941
Operating expenses:
Operating Expenses - Non-same store/other	1,259	496
NOI:
Net operating income - Non-same store/other	4,420	1,445
Total Assets	334,233
Capital Expenditures	258
All Other Markets | Same Store [Member]
Rental income:
Rental Income - Same Store	9,070	8,643
Operating expenses:
Operating Expenses - Same Store	3,765	4,131
NOI:
Net operating income - Same Store	5,305	4,512
Total Assets	126,515
Capital Expenditures	254
Other [Member] | Non-same store [Member]
Rental income:
Rental Income - Non-same store/other	39,411	129,219
Operating expenses:
Operating Expenses - Non-same store/other	16,464	44,397
NOI:
Net operating income - Non-same store/other	22,947	$ 84,822
Total Assets	2,341,173
Capital Expenditures	2,047
Same Store [Member]
NOI:
Total Assets	17,169,536
Capital Expenditures	28,108
Non-same store [Member]
NOI:
Total Assets	4,131,756
Capital Expenditures	$ 5,794