Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 348,723	$ 339,062	$ 695,978	$ 674,466
Deferred revenue	7,700		7,700		$ 9,300
Deferred revenue, revenue recognized			1,600
Deferred revenue balance from contracts with remaining performance obligations	7,700		7,700
Rental Income [Member]
Disaggregation of Revenue [Line Items]
Total revenues	323,020	314,546	644,681	624,668
Other Property Leasing Revenue [Member]
Disaggregation of Revenue [Line Items]
Total revenues	23,506	22,220	46,792	45,266
Management and Other Fees From Affiliates Income [Member]
Disaggregation of Revenue [Line Items]
Total revenues	2,197	2,296	4,505	4,532
Rental and Other Property Revenues [Member]
Disaggregation of Revenue [Line Items]
Total revenues	346,526	336,766	691,473	669,934
Rental and Other Property Revenues [Member] | Same Property [Member]
Disaggregation of Revenue [Line Items]
Total revenues	321,283	312,629	641,378	622,460
Rental and Other Property Revenues [Member] | Acquisitions [Member]
Disaggregation of Revenue [Line Items]
Total revenues	10,501	10,170	20,884	18,356
Rental and Other Property Revenues [Member] | Development [Member]
Disaggregation of Revenue [Line Items]
Total revenues	450	0	469	0
Rental and Other Property Revenues [Member] | Redevelopment [Member]
Disaggregation of Revenue [Line Items]
Total revenues	5,036	4,909	10,060	9,723
Rental and Other Property Revenues [Member] | Non-Residential/Other, Net [Member]
Disaggregation of Revenue [Line Items]
Total revenues	9,256	9,058	18,682	19,395
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Southern California [Member]
Disaggregation of Revenue [Line Items]
Total revenues	150,431	145,600	300,200	290,504
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Northern California [Member]
Disaggregation of Revenue [Line Items]
Total revenues	129,590	126,550	258,212	249,858
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Seattle Metro [Member]
Disaggregation of Revenue [Line Items]
Total revenues	58,795	57,087	117,509	113,279
Rental and Other Property Revenues [Member] | Other real estate assets [Member]
Disaggregation of Revenue [Line Items]
Total revenues	$ 7,710	$ 7,529	$ 15,552	$ 16,293
Minimum [Member]
Disaggregation of Revenue [Line Items]
Lease term	6 months		6 months
Maximum [Member]
Disaggregation of Revenue [Line Items]
Lease term	12 months		12 months