Related Party Transactions (Details) $ in Thousands	1 Months Ended					3 Months Ended		11 Months Ended	12 Months Ended
	Feb. 28, 2019 USD ($)	Oct. 31, 2018 USD ($) apartment	May 31, 2018 USD ($) apartment	Nov. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) unit	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($) investment	Nov. 30, 2016 USD ($)
Related Party Transaction [Line Items]
Management and other fees from affiliates						$ 3,400	$ 3,200
Development and redevelopment fees						1,100	900
Payments to acquire preferred equity investments						126,248	$ 56,020
Co-investments						1,307,561		$ 1,307,561	$ 1,300,140
Short-term loans outstanding and due from various joint ventures						3,900		3,900	4,500
Multifamily Development in Mountain View, California
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]
Preferred returns rate			10.25%
Number of units acquired | apartment			400
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] | BEX III [Member] | Secured Note Receivable, 3.5% Interest Rate, Due March 9, 2018 [Member]
Related Party Transaction [Line Items]
Notes receivable				$ 29,500
Notes Receivable, Related Party, Interest Rate				3.50%
Affiliated Entity [Member] | Multifamily Development in Mountain View, California
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]
Payments to acquire preferred equity investments		$ 18,600
Preferred returns rate		12.00%
Number of units acquired | apartment		268
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