Basis of Presentation - Statement of Partners' Equity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity				$ 1,798,508
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity	$ 1,687,709	$ 1,715,445	$ 1,745,042	1,798,508	$ 1,733,055	$ 1,805,756	$ 1,824,205	$ 1,799,955
General Partner Capital
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity				1,791,591
General Partner Capital | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity	$ 1,689,334	$ 1,715,685	1,740,552	1,791,591	1,720,870	1,794,623	1,814,960	1,795,684
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity				1,820,053
As Previously Reported | General Partner Capital
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity				1,813,136
As Previously Reported | General Partner Capital | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity			1,761,580		1,741,379	1,814,870	1,834,947	1,815,411
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity				(21,545)
Adjustments | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity				$ (21,545)
Adjustments | General Partner Capital | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Partners' equity			$ (21,028)		$ (20,509)	$ (20,247)	$ (19,987)	$ (19,727)