Organization, Ownership and Basis of Presentation - Operating Properties (Details)	Jun. 30, 2020 ft² building tenant project property_unit residential_unit
Stabilized office properties [Member]
Real Estate Properties [Line Items]
Number of Buildings | building	114
Rentable Square Feet | ft²	14,327,872
Number of Tenants | tenant	473
Percentage Occupied	92.30%
Percentage Leased	96.00%
Stabilized residential properties [Member]
Real Estate Properties [Line Items]
Number of Buildings | building	1
Percentage Occupied	89.30%
Number of Units | building	200
In-process development projects - tenant improvement [Member]
Real Estate Properties [Line Items]
Number of Buildings | project	3
Rentable Square Feet | ft²	1,275,000
In-process development projects - under construction [Member]
Real Estate Properties [Line Items]
Number of Buildings | project	5
Rentable Square Feet | ft²	1,016,000
Number of residential units | residential_unit	339
Completed residential development project [Member]
Real Estate Properties [Line Items]
Number of Buildings | project	2
Number of Units | property_unit	462