Organization, Ownership and Basis of Presentation - Operating Properties (Details)	Mar. 31, 2020 ft² building property_units tenant project residential_unit
Stabilized office properties [Member]
Real Estate Properties [Line Items]
Number of Buildings | building	114
Rentable Square Feet | ft²	14,323,572
Number of Tenants | tenant	479
Percentage Occupied	93.50%
Percentage Leased	97.30%
Stabilized residential properties [Member]
Real Estate Properties [Line Items]
Number of Buildings | building	1
Percentage Occupied	93.50%
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_units	462