Reportable Segments - NOI for Each Segment from Our Rental Real Estate Specific to Continuing Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Rental income	$ 2,571,705	$ 2,700,691	$ 2,577,681
Operating income	1,317,990	1,356,160	1,114,617
Total assets	20,286,891	21,172,769
Same Store
Segment Reporting Information [Line Items]
Rental income	2,419,018	2,519,235	2,377,066
Operating expenses	773,479	757,502	708,616
Operating income	1,645,539	1,761,733	1,668,450
Total assets	17,698,696	18,241,515
Capital Expenditures	132,281	171,135
Non-same store/other
Segment Reporting Information [Line Items]
Rental income	152,687	181,456	200,615
Operating expenses	49,081	55,482	78,533
Operating income	103,606	125,974	122,082
Total assets	2,588,195	2,931,254
Capital Expenditures	3,698	7,288
Same Store, Non-same Store and Other
Segment Reporting Information [Line Items]
Rental income	2,571,705	2,700,691	2,577,681
Operating expenses	822,560	812,984	787,149
Operating income	1,749,145	1,887,707	1,790,532
Total assets	20,286,891	21,172,769
Capital Expenditures	135,979	178,423
Other markets | Same Store
Segment Reporting Information [Line Items]
Rental income	17,605	18,215	1,940
Operating expenses	4,858	4,713	658
Operating income	12,747	13,502	1,282
Los Angeles | Same Store
Segment Reporting Information [Line Items]
Rental income	468,450	485,084	451,592
Operating expenses	145,342	144,314	129,455
Operating income	323,108	340,770	322,137
Total assets	3,007,621	3,110,659
Capital Expenditures	22,817	32,611
Subtotal - Southern California | Same Store
Segment Reporting Information [Line Items]
Rental income	648,423	663,869	644,761
Operating expenses	188,063	186,562	177,947
Operating income	460,360	477,307	466,814
Total assets	3,639,057	3,767,255
Capital Expenditures	33,507	45,834
Orange County | Same Store
Segment Reporting Information [Line Items]
Rental income	105,236	105,087	101,198
Operating expenses	24,545	24,359	24,468
Operating income	80,691	80,728	76,730
Total assets	389,007	404,545
Capital Expenditures	7,260	9,276
San Diego | Same Store
Segment Reporting Information [Line Items]
Rental income	74,737	73,698	91,971
Operating expenses	18,176	17,889	24,024
Operating income	56,561	55,809	67,947
Total assets	242,429	252,051
Capital Expenditures	3,430	3,947
Washington DC | Same Store
Segment Reporting Information [Line Items]
Rental income	389,533	394,171	403,761
Operating expenses	120,533	119,419	123,345
Operating income	269,000	274,752	280,416
Total assets	3,066,702	3,174,721
Capital Expenditures	23,626	22,409
New York | Same Store
Segment Reporting Information [Line Items]
Rental income	426,016	464,270	444,112
Operating expenses	198,228	191,514	178,055
Operating income	227,788	272,756	266,057
Total assets	3,950,286	4,004,078
Capital Expenditures	25,609	26,976
San Francisco | Same Store
Segment Reporting Information [Line Items]
Rental income	451,724	473,102	463,492
Operating expenses	119,183	115,702	112,331
Operating income	332,541	357,400	351,161
Total assets	3,233,901	3,345,882
Capital Expenditures	18,983	25,925
Boston | Same Store
Segment Reporting Information [Line Items]
Rental income	240,158	253,297	218,778
Operating expenses	71,611	70,875	60,409
Operating income	168,547	182,422	158,369
Total assets	1,758,665	1,822,373
Capital Expenditures	18,367	27,267
Seattle | Same Store
Segment Reporting Information [Line Items]
Rental income	245,559	252,311	200,222
Operating expenses	71,003	68,717	55,871
Operating income	174,556	183,594	144,351
Total assets	1,802,952	1,871,232
Capital Expenditures	11,372	22,023
Non-same store | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	116,103	58,751	103,688
Operating expenses	35,952	17,702	36,874
Operating income	80,151	41,049	66,814
Total assets	1,664,892	1,681,367
Capital Expenditures	2,627	1,864
Other | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	36,584	122,705	96,927
Operating expenses	13,129	37,780	41,659
Operating income	23,455	84,925	$ 55,268
Total assets	923,303	1,249,887
Capital Expenditures	1,071	5,424
Denver | Same Store
Segment Reporting Information [Line Items]
Total assets	247,133	255,974
Capital Expenditures	$ 817	$ 701