Acquisitions- Additional Information (Details)	Sep. 30, 2018 ft²	Jul. 17, 2017 USD ($) ft²
Business Acquisition [Line Items]
Area of office and retail properties | ft²	11,900,000
50 Beale Street [Member]
Business Acquisition [Line Items]
Percentage of ownership interest in new joint venture		36.60%
Percentage of interest acquired		62.20%
Area of office and retail properties | ft²		660,625
Percentage of interest directly acquired in property		13.20%
Percentage of remaining interest acquired in property by new joint venture.		49.00%
Property funds, ownership percentage		31.10%
Property funds, ownership amount | $		$ 517,500,000
Value of debt assumed with acquisition | $		$ 228,000,000