Organization of The Parent Company and The Operating Partnership - Summary of Core Portfolio of Operating Properties and Excludes Development and Redevelopment Properties Under Construction (Details)	Dec. 31, 2018 ft² property
Real Estate Properties [Line Items]
Number of Properties | property	97
Rentable Square Feet | ft²	16,777,249
Office Properties [Member]
Real Estate Properties [Line Items]
Number of Properties | property	88
Rentable Square Feet | ft²	15,609,156
Mixed-use Properties [Member]
Real Estate Properties [Line Items]
Number of Properties | property	4
Rentable Square Feet | ft²	646,741
Retail Property [Member]
Real Estate Properties [Line Items]
Number of Properties | property	1
Rentable Square Feet | ft²	17,884
Core Properties [Member]
Real Estate Properties [Line Items]
Number of Properties | property	93
Rentable Square Feet | ft²	16,273,781
Development Property [Member]
Real Estate Properties [Line Items]
Number of Properties | property	1
Rentable Square Feet | ft²	164,818
Redevelopment Properties [Member]
Real Estate Properties [Line Items]
Number of Properties | property	3
Rentable Square Feet | ft²	338,650