Reportable Segments - NOI for Each Segment from Our Rental Real Estate Specific to Continuing Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Rental income	$ 632,831	$ 603,920
Operating income	196,869	204,371
Total Assets	20,383,870		$ 20,570,599
Capital Expenditures	36,747
Same store
Segment Reporting Information [Line Items]
Rental income	590,384	577,404
Operating expenses	180,358	173,605
Operating income	410,026	403,799
Total Assets	17,612,333
Capital Expenditures	36,235
Non-same store/other
Segment Reporting Information [Line Items]
Rental income	42,447	26,516
Operating expenses	19,758	10,731
Operating income	22,689	15,785
Total Assets	2,771,537
Capital Expenditures	512
Same Store, Non-same Store and Other
Segment Reporting Information [Line Items]
Rental income	632,831	603,920
Operating expenses	200,116	184,336
Operating income	432,715	419,584
Other markets | Same store
Segment Reporting Information [Line Items]
Rental income	487	464
Operating expenses	165	196
Operating income	322	268
Total Assets	12,918
Capital Expenditures	77
Los Angeles | Same store
Segment Reporting Information [Line Items]
Rental income	102,484	98,636
Operating expenses	29,860	28,651
Operating income	72,624	69,985
Total Assets	2,670,909
Capital Expenditures	5,939
Orange County | Same store
Segment Reporting Information [Line Items]
Rental income	22,502	21,656
Operating expenses	5,527	5,462
Operating income	16,975	16,194
Total Assets	325,898
Capital Expenditures	1,620
San Diego | Same store
Segment Reporting Information [Line Items]
Rental income	22,493	21,723
Operating expenses	5,963	5,799
Operating income	16,530	15,924
Total Assets	417,593
Capital Expenditures	1,270
Subtotal - Southern California | Same store
Segment Reporting Information [Line Items]
Rental income	147,479	142,015
Operating expenses	41,350	39,912
Operating income	106,129	102,103
Total Assets	3,414,400
Capital Expenditures	8,829
San Francisco | Same store
Segment Reporting Information [Line Items]
Rental income	109,212	106,306
Operating expenses	26,995	26,928
Operating income	82,217	79,378
Total Assets	3,020,673
Capital Expenditures	8,743
Washington DC | Same store
Segment Reporting Information [Line Items]
Rental income	107,155	106,443
Operating expenses	33,663	32,332
Operating income	73,492	74,111
Total Assets	3,771,999
Capital Expenditures	5,964
New York | Same store
Segment Reporting Information [Line Items]
Rental income	119,626	119,363
Operating expenses	47,825	45,439
Operating income	71,801	73,924
Total Assets	4,447,994
Capital Expenditures	5,216
Boston | Same store
Segment Reporting Information [Line Items]
Rental income	57,814	56,388
Operating expenses	16,672	15,783
Operating income	41,142	40,605
Total Assets	1,637,837
Capital Expenditures	4,358
Seattle | Same store
Segment Reporting Information [Line Items]
Rental income	48,611	46,425
Operating expenses	13,688	13,015
Operating income	34,923	33,410
Total Assets	1,306,512
Capital Expenditures	3,048
Non-same store | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	38,622	15,961
Operating expenses	13,733	5,894
Operating income	24,889	10,067
Total Assets	2,276,821
Capital Expenditures	454
Other | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	3,825	10,555
Operating expenses	6,025	4,837
Operating income	(2,200)	$ 5,718
Total Assets	494,716
Capital Expenditures	$ 58