ORGANIZATION OF THE PARENT COMPANY AND THE OPERATING PARTNERSHIP - Narrative (Details)	9 Months Ended
	Sep. 30, 2023 a ft² property parcel
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of real estate properties | property	74
Rentable square feet	13,179,875
Unconsolidated Properties | Unconsolidated Real Estate Ventures
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of real estate properties | property	12
Parent Company
Organization of The Parent Company and The Operating Partnership [Line Items]
Rentable square feet	12,700,000
Areas of land held for development (in acres) | a	152.1
Lease agreement term	99 years
Area of additional undeveloped parcels of land with option to purchase (in acres) | a	55.1
Parent Company | Parcel of land
Organization of The Parent Company and The Operating Partnership [Line Items]
Lease agreement term	99 years
Parent Company | Leashold Interest Land
Organization of The Parent Company and The Operating Partnership [Line Items]
Areas of land held for development (in acres) | a	0.8
Number of parcels of land | parcel	1
Wholly-owned Management Company Subsidiaries
Organization of The Parent Company and The Operating Partnership [Line Items]
Rentable square feet	22,700,000
Wholly-owned Management Company Subsidiaries | Wholly Owned Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Rentable square feet	13,200,000
Wholly-owned Management Company Subsidiaries | Partially Owned Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Rentable square feet	9,500,000
Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	99.70%