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)	Mar. 31, 2018 ft² property
Real Estate Properties [Line Items]
Number of Properties | property	94
Rentable Square Feet | ft²	16,501,024
Office Properties [Member]
Real Estate Properties [Line Items]
Number of Properties | property	82
Rentable Square Feet | ft²	15,004,862
Mixed-use Properties [Member]
Real Estate Properties [Line Items]
Number of Properties | property	5
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	88
Rentable Square Feet | ft²	15,669,487
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	4
Rentable Square Feet | ft²	583,719