Related Party Transactions (Details) $ in Thousands	1 Months Ended						3 Months Ended		6 Months Ended		12 Months Ended			14 Months Ended
	Jun. 30, 2019 USD ($) apartment	Feb. 28, 2019 USD ($)	Oct. 31, 2018 USD ($) apartment	May 31, 2018 USD ($) apartment	Nov. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) unit	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($) investment	Jun. 30, 2019 USD ($)	Nov. 30, 2016 USD ($)
Related Party Transaction [Line Items]
Management and other fees from affiliates							$ 3,500	$ 3,200	$ 6,900	$ 6,400
Development and redevelopment fees							1,300	$ 1,000	2,400	1,900
Debt assumed in connection with acquisition									98,681	0
Payments to acquire real estate									47,585	5,476
Payments to acquire preferred equity investments									167,278	$ 97,826
Co-investments	$ 1,324,081						1,324,081		1,324,081		$ 1,300,140			$ 1,324,081
Short-term loans outstanding and due from various joint ventures	$ 4,000						4,000		4,000		4,500			4,000
Brio, Walnut Creek, California [Member]
Related Party Transaction [Line Items]
Number of units acquired | apartment	300
Payments to acquire real estate	$ 164,900
Debt assumed in connection with acquisition	98,700
Multifamily Development in Mountain View, California [Member]
Related Party Transaction [Line Items]
Preferred returns rate		11.00%
Commitment to fund preferred equity investment		$ 24,500
Apartment Home Community In Ventura, California [Member]
Related Party Transaction [Line Items]
Number of units acquired | apartment				400
Preferred returns rate				10.25%
Commitment to fund preferred equity investment				$ 26,500
Commitment funded amount														21,300
Membership Interest In Sage At Cupertino [Member]
Related Party Transaction [Line Items]
Number of units acquired | unit						230
Co-investments						$ 15,300
Equity method investment, ownership percentage acquired						40.50%
Contract price						$ 90,000
Mortgage encumbrance						$ 52,000
Affiliated Entity [Member] | Multifamily Development in Mountain View, California [Member]
Related Party Transaction [Line Items]
Payments to acquire preferred equity investments		$ 24,500
Preferred returns rate		11.00%
Affiliated Entity [Member] | Home Community Development in Burlingame, California [Member]
Related Party Transaction [Line Items]
Number of units acquired | apartment			268
Payments to acquire preferred equity investments			$ 18,600
Preferred returns rate			12.00%
Affiliated Entity [Member] | Related Party Bridge Loans on Property Acquired by Bex III [Member]
Related Party Transaction [Line Items]
Notes receivable					$ 29,500
Interest rate					3.50%
Limited Liability Company [Member]
Related Party Transaction [Line Items]
Payments to acquire preferred equity investments													$ 20,000
Number of preferred equity method investments acquired during period (in investments) | investment													3
Preferred stock, stated interest percentage													9.50%
Redeemed amount											5,000	$ 5,000
Limited Liability Company [Member] | Marcus and Millichamp Company TMMC Affiliate [Member] | Secured Note Receivable, 9.50% Interest Rate, Due October 2019 [Member]
Related Party Transaction [Line Items]
Notes receivable	$ 6,600						$ 6,600		$ 6,600		$ 6,600			$ 6,600	$ 6,600