Reportable Segments - NOI for Each Segment from Our Rental Real Estate Specific to Continuing Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Rental income	$ 2,700,691	$ 2,577,681	$ 2,470,689
Operating income	1,356,544	1,115,370	1,004,528
Total assets	21,172,769	20,394,209
Capital Expenditures	178,423	188,501
Same Store
Segment Reporting Information [Line Items]
Rental income	2,453,259	2,377,066	2,311,240
Operating expenses	734,553	708,616	681,198
Operating income	1,718,706	1,668,450	1,630,042
Total assets	17,015,372	17,328,625
Capital Expenditures	165,785	176,145
Non-same store/other
Segment Reporting Information [Line Items]
Rental income	247,432	200,615	159,449
Operating expenses	78,431	78,533	59,578
Operating income	169,001	122,082	99,871
Total assets	4,157,397	3,065,584
Capital Expenditures	12,638	12,356
Same Store, Non-same Store and Other
Segment Reporting Information [Line Items]
Rental income	2,700,691	2,577,681	2,470,689
Operating expenses	812,984	787,149	740,776
Operating income	1,887,707	1,790,532	1,729,913
Other markets | Same Store
Segment Reporting Information [Line Items]
Rental income	2,094	1,940	1,839
Operating expenses	714	658	652
Operating income	1,380	1,282	1,187
Total assets	12,931	12,781
Capital Expenditures	194	163
Los Angeles | Same Store
Segment Reporting Information [Line Items]
Rental income	468,517	451,592	402,192
Operating expenses	136,096	129,455	114,055
Operating income	332,421	322,137	288,137
Total assets	2,975,420	2,958,361
Capital Expenditures	31,738	28,574
Subtotal - Southern California | Same Store
Segment Reporting Information [Line Items]
Rental income	668,646	644,761	579,226
Operating expenses	185,139	177,947	158,672
Operating income	483,507	466,814	420,554
Total assets	3,769,502	3,781,851
Capital Expenditures	45,478	41,313
Orange County | Same Store
Segment Reporting Information [Line Items]
Rental income	105,087	101,198	88,527
Operating expenses	24,407	24,468	21,544
Operating income	80,680	76,730	66,983
Total assets	404,545	418,041
Capital Expenditures	9,276	8,214
San Diego | Same Store
Segment Reporting Information [Line Items]
Rental income	95,042	91,971	88,507
Operating expenses	24,636	24,024	23,073
Operating income	70,406	67,947	65,434
Total assets	389,537	405,449
Capital Expenditures	4,464	4,525
Washington DC | Same Store
Segment Reporting Information [Line Items]
Rental income	413,006	403,761	430,060
Operating expenses	125,688	123,345	129,720
Operating income	287,318	280,416	300,340
Total assets	3,370,750	3,484,045
Capital Expenditures	23,015	26,981
New York | Same Store
Segment Reporting Information [Line Items]
Rental income	454,448	444,112	454,945
Operating expenses	188,784	178,055	170,064
Operating income	265,664	266,057	284,881
Total assets	3,866,500	3,878,580
Capital Expenditures	25,132	23,126
San Francisco | Same Store
Segment Reporting Information [Line Items]
Rental income	480,499	463,492	430,501
Operating expenses	116,036	112,331	108,689
Operating income	364,463	351,161	321,812
Total assets	3,238,884	3,325,595
Capital Expenditures	28,153	42,497
Boston | Same Store
Segment Reporting Information [Line Items]
Rental income	227,547	218,778	223,595
Operating expenses	62,176	60,409	60,931
Operating income	165,371	158,369	162,664
Total assets	1,464,196	1,514,814
Capital Expenditures	23,823	24,000
Seattle | Same Store
Segment Reporting Information [Line Items]
Rental income	207,019	200,222	191,074
Operating expenses	56,016	55,871	52,470
Operating income	151,003	144,351	138,604
Total assets	1,292,609	1,330,959
Capital Expenditures	19,990	18,065
Non-same store | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	196,476	103,688	95,016
Operating expenses	62,591	36,874	30,742
Operating income	133,885	66,814	64,274
Total assets	3,447,497	1,990,102
Capital Expenditures	10,788	5,934
Other | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	50,956	96,927	64,433
Operating expenses	15,840	41,659	28,836
Operating income	35,116	55,268	$ 35,597
Total assets	709,900	1,075,482
Capital Expenditures	$ 1,850	$ 6,422