Basis of Presentation (Textual) (Details) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 15, 2019 USD ($)	Jan. 01, 2019 USD ($)	Jan. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($) $ / shares	Sep. 30, 2019 USD ($) lease acquisition $ / shares	Sep. 30, 2018 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 15, 2017 USD ($) ft²
Basis Of Presentation [Line Items]
Number of acquisitions for which adjustments have been made to correct errors related to of purchase price allocation | acquisition						2
Net income attributable to Brandywine Realty Trust				$ 6,772	$ (43,180)	$ 17,500	$ 13,637
Cumulative effect of accounting change		$ 5,336
Number of long-term ground leases | lease						6
Right of use asset - operating leases		22,400		21,828		$ 21,828			$ 0
Lease liability - operating leases		$ 22,400		$ 22,503		22,503			$ 0
Proceeds from the sale of properties						$ 41,546	16,771
Philadelphia Marine Center (Marine Piers)
Basis Of Presentation [Line Items]
Rentable area (in square feet) | ft²										181,900
Total sale price for property sold										$ 21,400
Initial cash consideration for property sold										12,000
Proceeds from the sale of properties	$ 11,200
Unrecorded gain receivable on property sold								$ 9,400		$ 9,400
Uncollectible Leases
Basis Of Presentation [Line Items]
Cumulative effect of accounting change			$ 700
Error Corrections and Prior Period Adjustments
Basis Of Presentation [Line Items]
Net income attributable to Brandywine Realty Trust					$ (300)		$ (800)
Net income per share amount (in dollars per share) | $ / shares					$ 0	$ (0.01)