Reportable Segments - NOI for Each Segment from Our Rental Real Estate Specific to Continuing Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Rental income	$ 662,302	$ 632,831
Operating income	209,969	339,082
Total Assets	20,768,811		$ 20,394,209
Capital Expenditures	34,018
Same store
Segment Reporting Information [Line Items]
Rental income	622,603	603,797
Operating expenses	191,323	183,181
Operating income	431,280	420,616
Total Assets	18,077,425
Capital Expenditures	31,798
Non-same store/other
Segment Reporting Information [Line Items]
Rental income	39,699	29,034
Operating expenses	15,189	16,935
Operating income	24,510	12,099
Total Assets	2,691,386
Capital Expenditures	2,220
Same Store, Non-same Store and Other
Segment Reporting Information [Line Items]
Rental income	662,302	632,831
Operating expenses	206,512	200,116
Operating income	455,790	432,715
Other markets | Same store
Segment Reporting Information [Line Items]
Rental income	522	488
Operating expenses	185	164
Operating income	337	324
Total Assets	12,852
Capital Expenditures	44
Los Angeles | Same store
Segment Reporting Information [Line Items]
Rental income	115,399	110,996
Operating expenses	34,484	32,041
Operating income	80,915	78,955
Total Assets	3,049,292
Capital Expenditures	7,061
Orange County | Same store
Segment Reporting Information [Line Items]
Rental income	25,828	24,803
Operating expenses	6,205	6,091
Operating income	19,623	18,712
Total Assets	415,698
Capital Expenditures	1,833
San Diego | Same store
Segment Reporting Information [Line Items]
Rental income	23,304	22,492
Operating expenses	6,127	5,964
Operating income	17,177	16,528
Total Assets	401,881
Capital Expenditures	630
Subtotal - Southern California | Same store
Segment Reporting Information [Line Items]
Rental income	164,531	158,291
Operating expenses	46,816	44,096
Operating income	117,715	114,195
Total Assets	3,866,871
Capital Expenditures	9,524
San Francisco | Same store
Segment Reporting Information [Line Items]
Rental income	121,761	117,352
Operating expenses	30,417	29,410
Operating income	91,344	87,942
Total Assets	3,400,898
Capital Expenditures	6,039
Washington DC | Same store
Segment Reporting Information [Line Items]
Rental income	110,784	108,528
Operating expenses	34,674	33,910
Operating income	76,110	74,618
Total Assets	3,749,155
Capital Expenditures	3,683
New York | Same store
Segment Reporting Information [Line Items]
Rental income	116,064	113,328
Operating expenses	49,089	45,549
Operating income	66,975	67,779
Total Assets	4,144,468
Capital Expenditures	3,754
Boston | Same store
Segment Reporting Information [Line Items]
Rental income	58,320	56,294
Operating expenses	16,611	16,199
Operating income	41,709	40,095
Total Assets	1,581,121
Capital Expenditures	5,981
Seattle | Same store
Segment Reporting Information [Line Items]
Rental income	50,621	49,516
Operating expenses	13,531	13,853
Operating income	37,090	35,663
Total Assets	1,322,060
Capital Expenditures	2,773
Non-same store | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	39,409	17,396
Operating expenses	13,293	7,105
Operating income	26,116	10,291
Total Assets	2,192,615
Capital Expenditures	2,220
Other [Member] | Non-same store/other
Segment Reporting Information [Line Items]
Rental income	290	11,638
Operating expenses	1,896	9,830
Operating income	(1,606)	$ 1,808
Total Assets	$ 498,771