ORGANIZATION OF THE PARENT COMPANY AND THE OPERATING PARTNERSHIP - Narrative (Details)	12 Months Ended
	Dec. 31, 2020 ft² a property managementCompany parcel
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property	82
Area of real estate property	13,852,464
Number of management companies | managementCompany	7
Wholly Owned Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Area of real estate property	13,900,000
Parent Company
Organization of The Parent Company and The Operating Partnership [Line Items]
Area of undeveloped parcels of land | a	228.5
Area of undeveloped land held for sale | a	35.2
Area of additional undeveloped parcels of land with option to purchase | a	55.5
Total potential development capacity	14,200,000
Parent Company | Land Parcel One
Organization of The Parent Company and The Operating Partnership [Line Items]
Lease agreement term	99 years
Parent Company | Land Parcel Two
Organization of The Parent Company and The Operating Partnership [Line Items]
Lease agreement term	99 years
Parent Company | Held for Sale Properties Included in Continuing Operations
Organization of The Parent Company and The Operating Partnership [Line Items]
Total potential development capacity	200,000
Wholly-owned Management Company Subsidiaries
Organization of The Parent Company and The Operating Partnership [Line Items]
Area of real estate property	24,700,000
Wholly-owned Management Company Subsidiaries | Wholly Owned Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Area of real estate property	13,900,000
Wholly-owned Management Company Subsidiaries | Partially Owned Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Area of real estate property	10,800,000
Leashold Interest Land
Organization of The Parent Company and The Operating Partnership [Line Items]
Lease agreement term	99 years
Leashold Interest Land | Parent Company
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | parcel	2
Undeveloped parcels of land held | a	1.8
Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	99.40%
BRSCO | BRANDYWINE OPERATING PARTNERSHIP, L.P. | Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	100.00%
BMH | BRANDYWINE OPERATING PARTNERSHIP, L.P. | Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	100.00%
BPI | BRANDYWINE OPERATING PARTNERSHIP, L.P. | Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	100.00%
BBL | BRANDYWINE OPERATING PARTNERSHIP, L.P. | Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	100.00%
BPM | BRANDYWINE OPERATING PARTNERSHIP, L.P. | Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	100.00%
BBS | BRANDYWINE OPERATING PARTNERSHIP, L.P. | Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	100.00%
BGCS | BRANDYWINE OPERATING PARTNERSHIP, L.P. | Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	100.00%
Unconsolidated Real Estate Ventures | Unconsolidated Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property	9