SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revised Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating properties	$ 4,006,459	$ 3,951,719
Accumulated depreciation	(973,318)	(885,407)	$ (913,297)
Operating real estate investments, net	3,054,797	3,066,312
Total assets	4,075,969	4,076,976
Additional paid-in-capital	3,192,158	3,200,312
Cumulative earnings	804,556	775,625
Total Brandywine Realty Trust's equity	1,677,877	1,798,827
Noncontrolling interests	10,426	12,201
Total beneficiaries' equity	1,688,303	1,811,028	$ 1,826,870	$ 1,864,388
Total liabilities and equity	$ 4,075,969	4,076,976
Total Brandywine Operating Partnership, L.P.'s equity		1,796,316
Total partners' equity		1,798,508
As previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating properties		3,953,319
Accumulated depreciation		(865,462)
Operating real estate investments, net		3,087,857
Total assets		4,098,521
Additional paid-in-capital		3,200,850
Cumulative earnings		796,513
Total Brandywine Realty Trust's equity		1,820,253
Noncontrolling interests		12,320
Total beneficiaries' equity		1,832,573
Total liabilities and equity		4,098,521
Total Brandywine Operating Partnership, L.P.'s equity		1,817,861
Total partners' equity		1,820,053
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating properties		(1,600)
Accumulated depreciation		(19,945)
Operating real estate investments, net		(21,545)
Total assets		(21,545)
Additional paid-in-capital		(538)
Cumulative earnings		(20,888)
Total Brandywine Realty Trust's equity		(21,426)
Noncontrolling interests		(119)
Total beneficiaries' equity		(21,545)
Total liabilities and equity		(21,545)
Total Brandywine Operating Partnership, L.P.'s equity		(21,545)
Total partners' equity		(21,545)
General Partner Capital
Error Corrections and Prior Period Adjustments Restatement [Line Items]
General Partnership Capital; 176,480,095 and 176,873,324 units issued and outstanding as of December 31, 2019 and December 31, 2018, respectively		1,791,591
General Partner Capital | As previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
General Partnership Capital; 176,480,095 and 176,873,324 units issued and outstanding as of December 31, 2019 and December 31, 2018, respectively		1,813,136
General Partner Capital | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
General Partnership Capital; 176,480,095 and 176,873,324 units issued and outstanding as of December 31, 2019 and December 31, 2018, respectively		$ (21,545)