Revenues - Disaggregation of Revenue (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 community	Sep. 30, 2020 apartment	Sep. 30, 2020	Dec. 31, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Rental and other property	$ 368,464	$ 364,504	$ 1,126,363	$ 1,077,767
Management and other fees from affiliates	2,347	2,428	7,312	7,023
Total revenues	370,811	366,932	1,133,675	1,084,790
Occupancy threshold for classification as stabilized							90.00%
Apartment communities owned (in communities)					247	1
Deferred revenue	3,300		3,300					$ 3,900
Deferred revenue, revenue recognized			600
Deferred revenue balance from contracts with remaining performance obligations	3,300		3,300
Rental income
Disaggregation of Revenue [Line Items]
Rental and other property	362,073	358,001	1,108,658	1,058,973
Other property
Disaggregation of Revenue [Line Items]
Rental and other property	6,391	6,503	17,705	18,794
Rental and other property revenues
Disaggregation of Revenue [Line Items]
Rental and other property	368,464	364,504	1,126,363	1,077,767
Rental and other property revenues | Same-property
Disaggregation of Revenue [Line Items]
Rental and other property	314,958	337,691	981,437	1,006,232
Rental and other property revenues | Acquisitions
Disaggregation of Revenue [Line Items]
Rental and other property	20,143	2,991	58,907	3,466
Rental and other property revenues | Development
Disaggregation of Revenue [Line Items]
Rental and other property	5,461	1,883	13,956	4,258
Rental and other property revenues | Redevelopment
Disaggregation of Revenue [Line Items]
Rental and other property	4,277	5,272	14,774	15,741
Rental and other property revenues | Non-residential/other, net
Disaggregation of Revenue [Line Items]
Rental and other property	23,625	16,667	57,289	48,070
Apartment communities owned (in communities) | community					3
Rental and other property revenues | Operating Segments | Southern California
Disaggregation of Revenue [Line Items]
Rental and other property	140,271	151,841	438,087	453,873
Rental and other property revenues | Operating Segments | Northern California
Disaggregation of Revenue [Line Items]
Rental and other property	148,712	140,509	462,558	411,694
Rental and other property revenues | Operating Segments | Seattle Metro
Disaggregation of Revenue [Line Items]
Rental and other property	60,617	61,052	184,310	180,942
Rental and other property revenues | Other real estate assets
Disaggregation of Revenue [Line Items]
Rental and other property	$ 18,864	$ 11,102	$ 41,408	$ 31,258