Revenues - (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) community	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 apartment	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Rental and other property	$ 1,486,150	$ 1,450,628	$ 1,390,870
Management and other fees from affiliates	9,598	9,527	9,183
Revenues	$ 1,495,748	1,460,155	1,400,053
Occupancy threshold for classification as stabilized					90.00%
Apartment communities owned (in communities)	246			2
Rental
Disaggregation of Revenue [Line Items]
Rental and other property	$ 1,462,161	1,425,585	1,366,590
Other Property Leasing Revenue
Disaggregation of Revenue [Line Items]
Rental and other property	23,989	25,043	24,280
Rental and Other Property
Disaggregation of Revenue [Line Items]
Rental and other property	1,486,150	1,450,628	1,390,870
Rental and Other Property | Same Property
Disaggregation of Revenue [Line Items]
Rental and other property	1,286,686	1,338,690	1,288,771
Rental and Other Property | Acquisitions
Disaggregation of Revenue [Line Items]
Rental and other property	78,666	7,704	0
Rental and Other Property | Development
Disaggregation of Revenue [Line Items]
Rental and other property	20,050	7,675	2,741
Rental and Other Property | Redevelopment
Disaggregation of Revenue [Line Items]
Rental and other property	19,054	21,058	20,413
Rental and Other Property | Non-residential/other, net
Disaggregation of Revenue [Line Items]
Rental and other property	$ 59,838	75,501	78,945
Apartment communities owned (in communities) | community	3
Rental and Other Property | Straight line rent concession
Disaggregation of Revenue [Line Items]
Rental and other property	$ 21,856	0	0
Rental and Other Property | Operating Segments | Southern California
Disaggregation of Revenue [Line Items]
Rental and other property	570,673	597,330	579,533
Rental and Other Property | Operating Segments | Northern California
Disaggregation of Revenue [Line Items]
Rental and other property	610,867	557,139	520,117
Rental and Other Property | Operating Segments | Seattle Metro
Disaggregation of Revenue [Line Items]
Rental and other property	243,900	243,060	234,138
Rental and Other Property | Other Real Estate Assets
Disaggregation of Revenue [Line Items]
Rental and other property	$ 60,710	$ 53,099	$ 57,082