Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 347,255	$ 335,404
Deferred revenue	8,500		$ 9,300
Deferred revenue, revenue recognized	800
Deferred revenue balance from contracts with remaining performance obligations	8,500
Rental Income [Member]
Disaggregation of Revenue [Line Items]
Total revenues	321,661	310,122
Other Property Leasing Revenue [Member]
Disaggregation of Revenue [Line Items]
Total revenues	23,286	23,046
Management And Other Fees From Affiliates Income [Member]
Disaggregation of Revenue [Line Items]
Total revenues	2,308	2,236
Rental And Other Property Revenues [Member]
Disaggregation of Revenue [Line Items]
Total revenues	344,947	333,168
Rental And Other Property Revenues [Member] | Same Property [Member]
Disaggregation of Revenue [Line Items]
Total revenues	322,385	312,024
Rental And Other Property Revenues [Member] | Acquisitions [Member]
Disaggregation of Revenue [Line Items]
Total revenues	10,383	8,186
Rental And Other Property Revenues [Member] | Development [Member]
Disaggregation of Revenue [Line Items]
Total revenues	19	0
Rental And Other Property Revenues [Member] | Redevelopment [Member]
Disaggregation of Revenue [Line Items]
Total revenues	5,024	4,814
Rental And Other Property Revenues [Member] | Non-Residential/Other, Net [Member]
Disaggregation of Revenue [Line Items]
Total revenues	7,136	8,144
Rental And Other Property Revenues [Member] | Other real estate assets [Member]
Disaggregation of Revenue [Line Items]
Total revenues	5,552	6,569
Rental And Other Property Revenues [Member] | Southern California [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Total revenues	152,060	147,099
Rental And Other Property Revenues [Member] | Northern California [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Total revenues	128,622	123,308
Rental And Other Property Revenues [Member] | Seattle Metro [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Total revenues	$ 58,713	$ 56,192
Minimum [Member]
Disaggregation of Revenue [Line Items]
Lease term	6 months
Maximum [Member]
Disaggregation of Revenue [Line Items]
Lease term	12 months