Reportable Segments - NOI for Each Segment from Our Rental Real Estate Specific to Continuing Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Rental income	$ 685,120	$ 652,677	$ 2,016,796	$ 1,925,128
Operating income	368,363	339,403	947,592	896,088
Total Assets	21,054,056		21,054,056		$ 20,394,209
Capital Expenditures			128,335
Same store
Segment Reporting Information [Line Items]
Rental income	649,712	628,454	1,857,679	1,798,638
Operating expenses	196,520	189,582	559,793	539,070
Operating income	453,192	438,872	1,297,886	1,259,568
Total Assets	17,385,849		17,385,849
Capital Expenditures			119,911
Non-same store/other
Segment Reporting Information [Line Items]
Rental income	35,408	24,223	159,117	126,490
Operating expenses	5,992	8,347	49,138	52,201
Operating income	29,416	15,876	109,979	74,289
Total Assets	3,668,207		3,668,207
Capital Expenditures			8,424
Same Store, Non-same Store and Other
Segment Reporting Information [Line Items]
Rental income	685,120	652,677	2,016,796	1,925,128
Operating expenses	202,512	197,929	608,931	591,271
Operating income	482,608	454,748	1,407,865	1,333,857
Other markets | Same store
Segment Reporting Information [Line Items]
Rental income	520	484	1,560	1,453
Operating expenses	168	164	545	503
Operating income	352	320	1,015	950
Total Assets	12,867		12,867
Capital Expenditures			165
Los Angeles | Same store
Segment Reporting Information [Line Items]
Rental income	122,506	118,864	350,841	337,047
Operating expenses	36,666	34,683	102,851	96,431
Operating income	85,840	84,181	247,990	240,616
Total Assets	3,002,609		3,002,609
Capital Expenditures			23,301
Orange County | Same store
Segment Reporting Information [Line Items]
Rental income	26,636	25,599	78,522	75,595
Operating expenses	6,382	6,203	18,583	18,434
Operating income	20,254	19,396	59,939	57,161
Total Assets	409,559		409,559
Capital Expenditures			7,460
San Diego | Same store
Segment Reporting Information [Line Items]
Rental income	24,064	23,215	71,088	68,640
Operating expenses	6,447	6,234	18,532	17,988
Operating income	17,617	16,981	52,556	50,652
Total Assets	394,352		394,352
Capital Expenditures			3,161
Subtotal - Southern California | Same store
Segment Reporting Information [Line Items]
Rental income	173,206	167,678	500,451	481,282
Operating expenses	49,495	47,120	139,966	132,853
Operating income	123,711	120,558	360,485	348,429
Total Assets	3,806,520		3,806,520
Capital Expenditures			33,922
San Francisco | Same store
Segment Reporting Information [Line Items]
Rental income	127,104	122,075	359,867	346,485
Operating expenses	31,438	30,420	87,104	84,581
Operating income	95,666	91,655	272,763	261,904
Total Assets	3,267,869		3,267,869
Capital Expenditures			19,422
Washington DC | Same store
Segment Reporting Information [Line Items]
Rental income	111,712	108,979	330,944	323,549
Operating expenses	34,797	34,549	101,969	100,575
Operating income	76,915	74,430	228,975	222,974
Total Assets	3,600,267		3,600,267
Capital Expenditures			16,517
New York | Same store
Segment Reporting Information [Line Items]
Rental income	117,382	114,407	340,828	332,474
Operating expenses	48,293	45,143	142,047	133,001
Operating income	69,089	69,264	198,781	199,473
Total Assets	3,915,125		3,915,125
Capital Expenditures			17,532
Boston | Same store
Segment Reporting Information [Line Items]
Rental income	59,354	56,724	169,576	163,292
Operating expenses	16,243	16,124	46,645	45,473
Operating income	43,111	40,600	122,931	117,819
Total Assets	1,479,159		1,479,159
Capital Expenditures			18,191
Seattle | Same store
Segment Reporting Information [Line Items]
Rental income	60,434	58,107	154,453	150,103
Operating expenses	16,086	16,062	41,517	42,084
Operating income	44,348	42,045	112,936	108,019
Total Assets	1,304,042		1,304,042
Capital Expenditures			14,162
Non-same store | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	32,171	8,160	136,353	69,334
Operating expenses	9,676	2,785	43,801	25,322
Operating income	22,495	5,375	92,552	44,012
Total Assets	3,109,994		3,109,994
Capital Expenditures			7,757
Other | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	3,237	16,063	22,764	57,156
Operating expenses	(3,684)	5,562	5,337	26,879
Operating income	6,921	$ 10,501	17,427	$ 30,277
Total Assets	$ 558,213		558,213
Capital Expenditures			$ 667