Reportable Segments - NOI for Each Segment from Our Rental Real Estate Specific to Continuing Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Rental income	$ 653,532	$ 669,374	$ 1,335,837	$ 1,331,676
Operating income	356,889	369,117	778,974	578,894
Total Assets	20,714,951		20,714,951		$ 21,172,769
Capital Expenditures			61,265
Same Store
Segment Reporting Information [Line Items]
Rental income	623,275	637,915	1,260,825	1,258,261
Operating expenses	190,021	190,277	386,742	382,188
Operating income	433,254	447,638	874,083	876,073
Total Assets	18,134,597		18,134,597
Capital Expenditures			59,634
Non-same store/other
Segment Reporting Information [Line Items]
Rental income	30,257	31,459	75,012	73,415
Operating expenses	9,469	9,630	26,296	24,231
Operating income	20,788	21,829	48,716	49,184
Total Assets	2,580,354		2,580,354
Capital Expenditures			1,631
Same Store, Non-same Store and Other
Segment Reporting Information [Line Items]
Rental income	653,532	669,374	1,335,837	1,331,676
Operating expenses	199,490	199,907	413,038	406,419
Operating income	454,042	469,467	922,799	925,257
Los Angeles | Same Store
Segment Reporting Information [Line Items]
Rental income	117,994	121,216	239,914	240,751
Operating expenses	35,013	35,688	71,930	72,145
Operating income	82,981	85,528	167,984	168,606
Total Assets	3,064,404		3,064,404
Capital Expenditures			13,070
Orange County | Same Store
Segment Reporting Information [Line Items]
Rental income	26,318	26,058	53,013	51,887
Operating expenses	5,953	5,966	12,167	12,142
Operating income	20,365	20,092	40,846	39,745
Total Assets	397,148		397,148
Capital Expenditures			3,458
San Diego | Same Store
Segment Reporting Information [Line Items]
Rental income	23,706	23,720	47,848	47,023
Operating expenses	6,100	5,978	12,417	12,126
Operating income	17,606	17,742	35,431	34,897
Total Assets	382,082		382,082
Capital Expenditures			1,993
Subtotal - Southern California | Same Store
Segment Reporting Information [Line Items]
Rental income	168,018	170,994	340,775	339,661
Operating expenses	47,066	47,632	96,514	96,413
Operating income	120,952	123,362	244,261	243,248
Total Assets	3,843,634		3,843,634
Capital Expenditures			18,521
San Francisco | Same Store
Segment Reporting Information [Line Items]
Rental income	116,303	118,044	236,580	234,514
Operating expenses	29,045	28,528	59,313	57,629
Operating income	87,258	89,516	177,267	176,885
Total Assets	3,288,932		3,288,932
Capital Expenditures			6,940
Washington DC | Same Store
Segment Reporting Information [Line Items]
Rental income	97,527	98,571	196,601	195,453
Operating expenses	28,680	29,409	59,331	59,389
Operating income	68,847	69,162	137,270	136,064
Total Assets	3,120,074		3,120,074
Capital Expenditures			10,534
New York | Same Store
Segment Reporting Information [Line Items]
Rental income	111,949	117,457	227,179	230,808
Operating expenses	48,130	47,626	98,581	96,067
Operating income	63,819	69,831	128,598	134,741
Total Assets	4,001,050		4,001,050
Capital Expenditures			10,429
Boston | Same Store
Segment Reporting Information [Line Items]
Rental income	59,990	62,751	123,673	124,671
Operating expenses	16,984	17,398	35,144	35,639
Operating income	43,006	45,353	88,529	89,032
Total Assets	1,790,996		1,790,996
Capital Expenditures			8,631
Seattle | Same Store
Segment Reporting Information [Line Items]
Rental income	63,378	63,695	127,073	124,029
Operating expenses	18,383	17,853	35,440	34,634
Operating income	44,995	45,842	91,633	89,395
Total Assets	1,838,484		1,838,484
Capital Expenditures			4,334
Denver | Same Store
Segment Reporting Information [Line Items]
Rental income	6,110	6,403	8,944	9,125
Operating expenses	1,733	1,831	2,419	2,417
Operating income	4,377	4,572	6,525	6,708
Total Assets	251,427		251,427
Capital Expenditures			245
Non-same store | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	24,631	4,000	58,629	14,374
Operating expenses	7,212	1,124	17,748	4,423
Operating income	17,419	2,876	40,881	9,951
Total Assets	1,642,289		1,642,289
Capital Expenditures			1,129
Other | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	5,626	27,459	16,383	59,041
Operating expenses	2,257	8,506	8,548	19,808
Operating income	3,369	$ 18,953	7,835	$ 39,233
Total Assets	$ 938,065		938,065
Capital Expenditures			$ 502