PARTNER'S 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
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic									(396)	(369)	(327)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted									(396)	(369)	(327)
Preferred Share distributions									0	0	(2,032)
Preferred share redemption charge									$ 0	$ 0	$ (3,181)
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 Partnership Unit:
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
BRANDYWINE OPERATING PARTNERSHIP, L.P.
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									(69)	(55)	(29)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic									(396)	(369)	(327)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted									(396)	(369)	(327)
Preferred Share distributions									0	0	(2,032)
Preferred share redemption charge									0	0	(3,181)
Net income attributable to common unitholders, Basic									34,064	135,048	115,608
Net income attributable to common unitholders, Diluted									$ 34,064	$ 135,048	$ 115,608
Denominator
Basic weighted average shares outstanding (in shares)									177,114,932	179,959,370	176,964,149
Contingent securities/Share based compensation (in shares)									553,872	1,121,744	1,323,816
Diluted weighted average shares outstanding (in shares)									177,668,804	181,081,114	178,287,965
Earnings per Common Partnership Unit:
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