Organization of The Parent Company and The Operating Partnership - Narrative (Details)	6 Months Ended
	Jun. 30, 2021 a ft² property parcel
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property	81
Rentable Square Feet	13,653,199
Unconsolidated Properties | Unconsolidated Real Estate Ventures
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property	10
Parent Company
Organization of The Parent Company and The Operating Partnership [Line Items]
Areas of land held for development (in acres) | a	216.3
Area of land held for sale (in acres) | a	35.2
Lease agreement term	99 years
Area of additional undeveloped parcels of land with option to purchase (in acres) | a	55.5
Total potential development capacity (in square feet)	13,700,000
Parent Company | Land Parcel One
Organization of The Parent Company and The Operating Partnership [Line Items]
Lease agreement term	99 years
Parent Company | Held-for-sale
Organization of The Parent Company and The Operating Partnership [Line Items]
Total potential development capacity (in square feet)	200,000
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	24,500,000
Wholly-owned Management Company Subsidiaries | Wholly Owned Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Rentable Square Feet	13,700,000
Wholly-owned Management Company Subsidiaries | Partially Owned Properties
Organization of The Parent Company and The Operating Partnership [Line Items]
Rentable Square Feet	10,800,000
Brandywine Operating Partnership LP
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the operating partnership	99.50%