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Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
Revenues (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 1,400,053	$ 1,363,899	$ 1,294,001
Deferred revenue	6,200	9,300
Deferred revenue, revenue recognized	3,100
Deferred revenue balance from contracts with remaining performance obligations	6,200
Rental [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,296,435	1,263,476	1,201,995
Other Property Leasing Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	94,435	90,849	83,728
Management and other fees from affiliates [Member]
Disaggregation of Revenue [Line Items]
Revenues	9,183	9,574	8,278
Rental and other property [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,390,870	1,354,325	1,285,723
Rental and other property [Member] \| Same Property [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,279,640	1,244,743	1,185,685
Rental and other property [Member] \| Acquisitions [Member]
Disaggregation of Revenue [Line Items]
Revenues	42,481	39,289	0
Rental and other property [Member] \| Development [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,713	0	0
Rental and other property [Member] \| Redevelopment [Member]
Disaggregation of Revenue [Line Items]
Revenues	20,345	19,641	18,737
Rental and other property [Member] \| Non-Residential/Other, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	45,691	50,652	81,301
Rental and other property [Member] \| Operating Segments [Member] \| Southern California [Member]
Disaggregation of Revenue [Line Items]
Revenues	592,281	574,552	540,000
Rental and other property [Member] \| Operating Segments [Member] \| Northern California [Member]
Disaggregation of Revenue [Line Items]
Revenues	522,561	505,313	453,140
Rental and other property [Member] \| Operating Segments [Member] \| Seattle Metro [Member]
Disaggregation of Revenue [Line Items]
Revenues	236,525	229,871	217,259
Rental and other property [Member] \| Other real estate assets [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 39,503	$ 44,589	$ 75,324
Minimum [Member]
Disaggregation of Revenue [Line Items]
Lease term	6 months
Maximum [Member]
Disaggregation of Revenue [Line Items]
Lease term	12 months