Beneficiaries Equity of the Parent Company - Number of Shares and Net Income Used to Calculate Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator
Net income	$ 276,133	$ 4,020	$ 8,087	$ 6,820	$ 6,252	$ 4,583	$ 288,240	$ 17,655
Net income attributable to noncontrolling interests, Basic	(1,612)			(48)			(1,701)	(155)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic	(93)			(93)			(317)	(305)
Net income attributable to noncontrolling interests, Diluted	(1,612)			(48)			(1,701)	(155)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted	(93)			(93)			(317)	(305)
Net income attributable to Common Shareholders of Brandywine Realty Trust	274,428			6,679			286,222	17,195
Net income attributable to common shareholders, Diluted	$ 274,428			$ 6,679			$ 286,222	$ 17,195
Denominator
Basic weighted average shares outstanding (in shares)	170,573,028			176,195,244			172,380,410	176,066,507
Contingent securities/Share based compensation (in shares)	453,464			555,356			355,026	551,219
Diluted weighted average shares outstanding (in shares)	171,026,492			176,750,600			172,735,436	176,617,726
Earnings per Common Share:
Net income attributable to common shareholders, Basic (USD per share)	$ 1.61			$ 0.04			$ 1.66	$ 0.10
Net income attributable to common shareholders, Diluted (USD per share)	$ 1.60			$ 0.04			$ 1.66	$ 0.10