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)	Jun. 30, 2018 ft² property
Real Estate Properties [Line Items]
Number of Properties | property	93
Rentable Square Feet | ft²	16,462,764
Office Properties [Member]
Real Estate Properties [Line Items]
Number of Properties | property	81
Rentable Square Feet | ft²	14,966,602
Mixed-use Properties [Member]
Real Estate Properties [Line Items]
Number of Properties | property	4
Rentable Square Feet | ft²	646,741
Retail Properties [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	86
Rentable Square Feet | ft²	15,631,227
Development Projects [Member]
Real Estate Properties [Line Items]
Number of Properties | property	2
Rentable Square Feet | ft²	247,818
Redevelopment Projects [Member]
Real Estate Properties [Line Items]
Number of Properties | property	5
Rentable Square Feet | ft²	583,719