BENEFICIARIES' EQUITY OF THE PARENT COMPANY - Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator
Net income	$ 16,874	$ 6,820	$ 6,252	$ 4,583	$ 121,673	$ (43,522)	$ 12,876	$ 44,445	$ 34,529	$ 135,472	$ 121,177
Net income attributable to noncontrolling interests, Basic									(262)	(954)	(1,004)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic									(396)	(369)	(327)
Distribution to preferred shareholders									0	0	(2,032)
Preferred share redemption charge									0	0	(3,181)
Net income attributable to Common Shareholders/ Unitholders of Brandywine Realty Trust									33,871	134,149	114,633
Net income attributable to noncontrolling interests, Diluted									(262)	(954)	(1,004)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted									(396)	(369)	(327)
Net income attributable to common shareholders, Diluted									$ 33,871	$ 134,149	$ 114,633
Denominator
Basic weighted average shares outstanding (in shares)									176,132,941	178,519,748	175,484,350
Contingent securities/Share based compensation (in shares)									553,872	1,121,744	1,323,816
Diluted weighted average shares outstanding (in shares)									176,686,813	179,641,492	176,808,166
Earnings per Common Share:
Net income attributable to common shareholders, Basic (USD per share)	$ 0.09	$ 0.04	$ 0.03	$ 0.03	$ 0.68	$ (0.24)	$ 0.07	$ 0.25	$ 0.19	$ 0.75	$ 0.65
Net income attributable to common shareholders, Diluted (USD per share)	$ 0.09	$ 0.04	$ 0.03	$ 0.03	$ 0.67	$ (0.24)	$ 0.07	$ 0.24	$ 0.19	$ 0.75	$ 0.65