Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 350,917	$ 344,369	$ 1,046,895	$ 1,018,835
Deferred revenue	6,900		6,900		$ 9,300
Deferred revenue, revenue recognized			2,400
Deferred revenue balance from contracts with remaining performance obligations	6,900		6,900
Rental [Member]
Disaggregation of Revenue [Line Items]
Total revenues	324,780	319,308	969,461	943,976
Other Property Leasing Revenue [Member]
Disaggregation of Revenue [Line Items]
Total revenues	23,830	22,666	70,622	67,932
Management and Other Fees From Affiliates Income [Member]
Disaggregation of Revenue [Line Items]
Total revenues	2,307	2,395	6,812	6,927
Rental and Other Property Revenues [Member]
Disaggregation of Revenue [Line Items]
Total revenues	348,610	341,974	1,040,083	1,011,908
Rental and Other Property Revenues [Member] | Same Property [Member]
Disaggregation of Revenue [Line Items]
Total revenues	324,271	317,302	965,649	939,762
Rental and Other Property Revenues [Member] | Acquisitions [Member]
Disaggregation of Revenue [Line Items]
Total revenues	10,695	10,498	31,579	28,854
Rental and Other Property Revenues [Member] | Development [Member]
Disaggregation of Revenue [Line Items]
Total revenues	1,091	0	1,560	0
Rental and Other Property Revenues [Member] | Redevelopment [Member]
Disaggregation of Revenue [Line Items]
Total revenues	5,125	4,913	15,185	14,636
Rental and Other Property Revenues [Member] | Non-Residential/Other, Net [Member]
Disaggregation of Revenue [Line Items]
Total revenues	7,428	9,261	26,110	28,656
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Southern California [Member]
Disaggregation of Revenue [Line Items]
Total revenues	151,847	148,150	452,047	438,654
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Northern California [Member]
Disaggregation of Revenue [Line Items]
Total revenues	131,538	127,673	389,750	377,531
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Seattle Metro [Member]
Disaggregation of Revenue [Line Items]
Total revenues	59,231	58,285	176,740	171,564
Rental and Other Property Revenues [Member] | Other real estate assets [Member]
Disaggregation of Revenue [Line Items]
Total revenues	$ 5,994	$ 7,866	$ 21,546	$ 24,159
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