Related Party Transactions (Details) $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Nov. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) unit	Mar. 31, 2018 USD ($) investment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($) investment	Nov. 30, 2016 USD ($)
Related Party Transaction [Line Items]
Management and other fees from affiliates			$ 3,200	$ 3,000
Development and redevelopment fees			900	800
Co-investments			1,290,957		$ 1,155,984
Payments to acquire preferred equity investments			$ 56,020	120,816
Equity investment, redeemed amount					5,000
Number of equity method investments scheduled to mature | investment			2
Short-term loans outstanding and due from various joint ventures			$ 3,300		5,100
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
Note receivable, related party, 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%
Limited Liability Company [Member] | Marcus and Millichamp Company TMMC Affiliate [Member] | Secured Note Receivable, 9.5% Interest Rate, Due October 2019 [Member]
Related Party Transaction [Line Items]
Notes receivable			$ 6,600		$ 6,700		$ 6,600
Membership Interest In Sage At Cupertino [Member]
Related Party Transaction [Line Items]
Co-investments		$ 15,300		15,300
Number of units acquired | unit		230
Equity method investment, ownership percentage acquired		40.50%
Contract price		$ 90,000
Mortgage encumbrance		$ 52,000		$ 52,000