Organization of The Parent Company and The Operating Partnership - Summary of Core Portfolio of Operating Properties and Excludes Development, Redevelopment and Held for Sale (Details)	Sep. 30, 2019 ft² property
Real Estate Properties [Line Items]
Number of properties | property	95
Net rentable area (in square feet) | ft²	16,711,387
Office properties
Real Estate Properties [Line Items]
Number of properties | property	87
Net rentable area (in square feet) | ft²	15,509,004
Mixed-use properties
Real Estate Properties [Line Items]
Number of properties | property	3
Net rentable area (in square feet) | ft²	641,741
Retail property
Real Estate Properties [Line Items]
Number of properties | property	1
Net rentable area (in square feet) | ft²	17,884
Core Properties
Real Estate Properties [Line Items]
Number of properties | property	91
Net rentable area (in square feet) | ft²	16,168,629
Development property
Real Estate Properties [Line Items]
Number of properties | property	1
Net rentable area (in square feet) | ft²	204,108
Redevelopment properties
Real Estate Properties [Line Items]
Number of properties | property	3
Net rentable area (in square feet) | ft²	338,650