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	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator
Net income	$ 12,366	$ 307,326	$ 34,529
Net income attributable to noncontrolling interests, Basic	(77)	(1,799)	(262)
Net income attributable to noncontrolling interests, Diluted	(77)	(1,799)	(262)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic	(421)	(410)	(396)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted	(421)	(410)	(396)
Net income attributable to Common Shareholders/ Unitholders of Brandywine Realty Trust	11,868	305,117	33,871
Net income attributable to common shareholders, Diluted	$ 11,868	$ 305,117	$ 33,871
Denominator
Basic weighted average shares outstanding (in shares)	170,878,185	171,926,079	176,132,941
Contingent securities/Share based compensation (in shares)	1,395,055	390,997	553,872
Diluted weighted average shares outstanding (in shares)	172,273,240	172,317,076	176,686,813
Earnings per Common Share:
Net income attributable to common shareholders, Basic (in dollars per share)	$ 0.07	$ 1.77	$ 0.19
Net income attributable to common shareholders, Diluted (in dollars per share)	$ 0.07	$ 1.77	$ 0.19