PARTNER'S 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
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic	(410)	(396)	(369)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted	$ (410)	$ (396)	$ (369)
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 Partnership Unit:
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
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Numerator
Net income	$ 307,326	$ 34,529	$ 135,472
Net income attributable to noncontrolling interests	(20)	(69)	(55)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic	(410)	(396)	(369)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted	(410)	(396)	(369)
Net income attributable to common unitholders, Basic	306,896	34,064	135,048
Net income attributable to common unitholders, Diluted	$ 306,896	$ 34,064	$ 135,048
Denominator
Basic weighted average shares outstanding (in shares)	172,907,713	177,114,932	179,959,370
Contingent securities/Share based compensation (in shares)	390,997	553,872	1,121,744
Diluted weighted average shares outstanding (in shares)	173,298,710	177,668,804	181,081,114
Earnings per Common Partnership Unit:
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