Organization, Ownership and Basis of Presentation - Operating Properties (Details) - Jun. 30, 2019	ft²	Total	building	property	project	residential_unit	tenant
Office properties [Member]
Real Estate Properties [Line Items]
Number of Buildings			94	4
Rentable Square Feet	13,546,615
Number of Tenants | tenant							461
Percentage Occupied		93.80%
Percentage Leased		97.20%
Stabilized Residential Properties [Member]
Real Estate Properties [Line Items]
Number of Buildings | building			1
Percentage Occupied		73.40%
Number of Units | building			200
In-process development projects - tenant improvement [Member]
Real Estate Properties [Line Items]
Number of Buildings | project					2
Rentable Square Feet	846,000
In-process development projects - under construction [Member]
Real Estate Properties [Line Items]
Number of Buildings | project					5
Rentable Square Feet	2,095,000
In-process development projects - under construction [Member] | Retail site [Member]
Real Estate Properties [Line Items]
Rentable Square Feet	96,000
Number of residential units | residential_unit						801