Related Party Transactions (Details)	1 Months Ended										3 Months Ended		9 Months Ended		41 Months Ended
	Sep. 30, 2021 USD ($)	Aug. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Jan. 31, 2021 USD ($)	Nov. 30, 2019 USD ($) apartment	Jun. 30, 2019 USD ($) apartment	Feb. 28, 2019 USD ($)	Oct. 31, 2018 USD ($) apartment	May 31, 2018 USD ($) apartment	Mar. 31, 2017 USD ($) unit	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Related Party Transaction [Line Items]
Payments to acquire preferred equity investments													$ 223,175,000	$ 61,056,000
Preferred return rate	12.50%	11.50%		10.00%
Commitment to fund preferred equity investment	$ 26,200,000	$ 11,000,000		$ 20,000,000
Co-investments	1,081,861,000										$ 1,081,861,000		1,081,861,000		$ 1,081,861,000	$ 1,018,010,000
Membership Interest In Sage At Cupertino
Related Party Transaction [Line Items]
Number of units acquired | unit										230
Co-investments										$ 15,300,000
Investment interest acquired										40.50%
Contract price										$ 90,000,000
Encumbrance										$ 52,000,000
Affiliated Entity
Related Party Transaction [Line Items]
Management and other fees from affiliates											2,700,000	$ 3,000,000	7,500,000	8,700,000
Development and redevelopment fees											500,000	600,000	800,000	1,400,000
Short-term loans outstanding and due from affiliates	33,900,000										33,900,000		33,900,000		33,900,000	$ 4,700,000
Affiliated Entity | Apartment Home Community In Seattle, WA
Related Party Transaction [Line Items]
Number of units acquired | apartment					308
Affiliated Entity | Related party bridge loan - Wesco VI
Related Party Transaction [Line Items]
Notes receivable	$ 29,200,000										29,200,000		29,200,000		29,200,000
Interest rate	2.15%
Affiliated Entity | Related party bridge loan - Wesco I
Related Party Transaction [Line Items]
Notes receivable			$ 52,500,000
Interest rate			2.55%
Affiliated Entity | Related party bridge loan - Wesco V | Apartment Home Community In Seattle, WA
Related Party Transaction [Line Items]
Notes receivable					$ 85,500,000
Interest rate					1.30%
Chairman and founder | Multifamily development community in Mountain View, CA
Related Party Transaction [Line Items]
Payments to acquire preferred equity investments							$ 24,500,000
Preferred return rate							11.00%
Chairman and founder | Apartment home community development development in Burlingame, CA
Related Party Transaction [Line Items]
Number of units acquired | apartment								268
Payments to acquire preferred equity investments								$ 18,600,000
Preferred return rate								12.00%
Chairman and founder | Marcus & Millichap Company (MMC)
Related Party Transaction [Line Items]
Brokerage commissions											$ 0	$ 0	$ 0	$ 200,000
Chairman and founder | Marcus & Millichap Company (MMC) | Brio, Walnut Creek, CA
Related Party Transaction [Line Items]
Number of units acquired | apartment						300
Payments to acquire real estate						$ 164,900,000
Debt assumed in connection with acquisition						$ 98,700,000
Chairman and founder | Marcus & Millichap Company (MMC) | Apartment home community in Ventura, CA
Related Party Transaction [Line Items]
Number of units acquired | apartment									400
Preferred return rate									10.25%
Commitment to fund preferred equity investment									$ 26,500,000
Commitment funded amount															$ 23,400,000