BENEFICIARIES' EQUITY OF THE PARENT COMPANY - Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator
Net income	$ 307,326	$ 34,529	$ 135,472
Net income attributable to noncontrolling interests, Basic	(1,799)	(262)	(954)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic	(410)	(396)	(369)
Net income attributable to Common Shareholders/ Unitholders of Brandywine Realty Trust	305,117	33,871	134,149
Net income attributable to noncontrolling interests, Diluted	(1,799)	(262)	(954)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted	(410)	(396)	(369)
Net income attributable to common shareholders, Diluted	$ 305,117	$ 33,871	$ 134,149
Denominator
Basic weighted average shares outstanding (in shares)	171,926,079	176,132,941	178,519,748
Contingent securities/Share based compensation (in shares)	390,997	553,872	1,121,744
Diluted weighted average shares outstanding (in shares)	172,317,076	176,686,813	179,641,492
Earnings per Common Share:
Net income attributable to common shareholders, Basic (USD per share)	$ 1.77	$ 0.19	$ 0.75
Net income attributable to common shareholders, Diluted (USD per share)	$ 1.77	$ 0.19	$ 0.75