ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Parent Company
Beneficiaries' Equity, beginning balance		$ 1,804,648	$ 1,688,303	$ 1,811,028
Change in fair market value during year		4,817	(5,972)	(8,210)
Allocation of unrealized (gains)/losses on derivative financial instruments to noncontrolling interests		(28)	29	41
Amortization of interest rate contracts reclassified from comprehensive income to interest expense	[1]	752	752	770
Beneficiaries' Equity, ending balance		1,701,219	1,804,648	1,688,303
Operating Partnership
Change in fair market value during year		4,817	(5,972)	(8,210)
Amortization of interest rate contracts reclassified from comprehensive income to interest expense	[1]	752	752	770
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Parent Company
Change in fair market value during year		4,817	(5,972)	(8,210)
Amortization of interest rate contracts reclassified from comprehensive income to interest expense	[1]	752	752	770
Operating Partnership
Partners' Equity, beginning balance		1,793,082	1,672,915	1,798,508
Change in fair market value during year		4,817	(5,972)	(8,210)
Amortization of interest rate contracts reclassified from comprehensive income to interest expense	[1]	752	752	770
Partners' Equity, ending balance		1,690,079	1,793,082	1,672,915
Accumulated Other Comprehensive Income (Loss)
Parent Company
Beneficiaries' Equity, beginning balance		(7,561)	(2,370)	5,029
Beneficiaries' Equity, ending balance		(2,020)	(7,561)	(2,370)
Accumulated Other Comprehensive Income (Loss) | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Operating Partnership
Partners' Equity, beginning balance		(7,935)	(2,715)	4,725
Partners' Equity, ending balance		$ (2,366)	$ (7,935)	$ (2,715)

[1] Amounts reclassified from comprehensive income to interest expense within the Consolidated Statements of Operations.