Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 366,932	$ 350,917	$ 1,084,790	$ 1,046,895
Occupancy threshold for classification as stabilized	95.00%		95.00%
Deferred revenue	$ 4,100		$ 4,100		$ 6,200
Deferred revenue, revenue recognized			2,100
Deferred revenue balance from contracts with remaining performance obligations	4,100		4,100
Rental [Member]
Disaggregation of Revenue [Line Items]
Total revenues	358,001	342,246	1,058,973	1,021,742
Other Property [Member]
Disaggregation of Revenue [Line Items]
Total revenues	6,503	6,364	18,794	18,341
Management and Other Fees From Affiliates Income [Member]
Disaggregation of Revenue [Line Items]
Total revenues	2,428	2,307	7,023	6,812
Rental and Other Property Revenues [Member]
Disaggregation of Revenue [Line Items]
Total revenues	364,504	348,610	1,077,767	1,040,083
Rental and Other Property Revenues [Member] | Same Property [Member]
Disaggregation of Revenue [Line Items]
Total revenues	342,115	331,695	1,019,509	987,564
Rental and Other Property Revenues [Member] | Acquisitions [Member]
Disaggregation of Revenue [Line Items]
Total revenues	7,309	0	14,416	0
Rental and Other Property Revenues [Member] | Development [Member]
Disaggregation of Revenue [Line Items]
Total revenues	1,859	1,091	4,184	1,560
Rental and Other Property Revenues [Member] | Redevelopment [Member]
Disaggregation of Revenue [Line Items]
Total revenues	5,255	5,125	15,690	15,185
Rental and Other Property Revenues [Member] | Non-Residential/Other, Net [Member]
Disaggregation of Revenue [Line Items]
Total revenues	7,966	10,699	23,968	35,774
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Southern California [Member]
Disaggregation of Revenue [Line Items]
Total revenues	152,312	148,575	455,302	442,382
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Northern California [Member]
Disaggregation of Revenue [Line Items]
Total revenues	144,124	131,538	420,544	389,750
Rental and Other Property Revenues [Member] | Operating Segments [Member] | Seattle Metro [Member]
Disaggregation of Revenue [Line Items]
Total revenues	61,657	59,231	182,738	176,740
Rental and Other Property Revenues [Member] | Other real estate assets [Member]
Disaggregation of Revenue [Line Items]
Total revenues	$ 6,411	$ 9,266	$ 19,183	$ 31,211