Organization of The Parent Company and The Operating Partnership - Narrative (Details)	3 Months Ended
	Mar. 31, 2021 a ft² parcel property
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties | property	81
Net rentable area (in square feet)	13,651,396
Parent Company
Organization of The Parent Company and The Operating Partnership [Line Items]
Areas of land held for development (in acres) | a	228.5
Area of land held for sale (in acres) | a	35.2
Area of additional undeveloped parcels of land with option to purchase (in acres) | a	55.5
Total potential development capacity (in square feet)	13,900,000
Wholly-owned Management Company Subsidiaries
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable area (in square feet)	24,500,000
Wholly Owned Properties | Wholly-owned Management Company Subsidiaries
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable area (in square feet)	13,700,000
Partially Owned Properties | Wholly-owned Management Company Subsidiaries
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable area (in square feet)	10,800,000
Land Parcel One | Parent Company
Organization of The Parent Company and The Operating Partnership [Line Items]
Lease agreement term	99 years
Land Parcel Two | Parent Company
Organization of The Parent Company and The Operating Partnership [Line Items]
Lease agreement term	99 years
Held-for-sale | Parent Company
Organization of The Parent Company and The Operating Partnership [Line Items]
Total potential development capacity (in square feet)	200,000
Leashold Interest Land | Parent Company
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
Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	99.40%
Unconsolidated Real Estate Ventures | Unconsolidated Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties | property	10