ORGANIZATION OF THE PARENT COMPANY AND THE OPERATING PARTNERSHIP - Summary of Properties (Details)	Dec. 31, 2019 ft² property
Real Estate Properties [Line Items]
Number of Properties | property	95
Rentable Square Feet | ft²	16,711,387
Office Properties
Real Estate Properties [Line Items]
Number of Properties | property	86
Rentable Square Feet | ft²	15,450,417
Mixed-use Properties
Real Estate Properties [Line Items]
Number of Properties | property	4
Rentable Square Feet | ft²	659,625
Core Properties
Real Estate Properties [Line Items]
Number of Properties | property	90
Rentable Square Feet | ft²	16,110,042
Development Property
Real Estate Properties [Line Items]
Number of Properties | property	1
Rentable Square Feet | ft²	204,108
Redevelopment Properties
Real Estate Properties [Line Items]
Number of Properties | property	4
Rentable Square Feet | ft²	397,237