Beneficiaries Equity of the Parent Company - Number of Shares and Net Income Used to Calculate Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator
Net income	$ 122,710	[1]	$ (43,262)	[2]	$ 13,136	$ 44,705	$ 73,844	$ 19,046	$ 7,698	$ 21,271	$ 137,289	$ 121,859	$ 40,501
Net income attributable to noncontrolling interests, Basic											(965)	(1,009)	(310)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic											(369)	(327)	(341)
Distribution to preferred shareholders											0	(2,032)	(6,900)
Preferred share redemption charge											0	(3,181)	0
Net income attributable to Common Shareholders of Brandywine Realty Trust											135,955	115,310	32,950
Net income attributable to noncontrolling interests, Diluted											(965)	(1,009)	(310)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted											(369)	(327)	(341)
Net income attributable to common shareholders, Diluted											$ 135,955	$ 115,310	$ 32,950
Denominator
Basic weighted average shares outstanding (in shares)											178,519,748	175,484,350	175,018,163
Contingent securities/Share based compensation (in shares)											1,121,744	1,323,816	992,651
Diluted weighted average shares outstanding (in shares)											179,641,492	176,808,166	176,010,814
Earnings per Common Share:
Net income attributable to common shareholders, Basic (USD per share)	$ 0.68		$ (0.24)		$ 0.07	$ 0.25	$ 0.42	$ 0.11	$ 0.02	$ 0.11	$ 0.76	$ 0.66	$ 0.19
Net income attributable to common shareholders, Diluted (USD per share)	$ 0.68		$ (0.24)		$ 0.07	$ 0.25	$ 0.41	$ 0.11	$ 0.02	$ 0.11	$ 0.76	$ 0.65	$ 0.19

[1] The increase in net income for the fourth quarter primarily relates to gains of $103.8 million and $28.3 million, recorded in the “Net gain on real estate venture transactions” and “Gain on promoted interest in unconsolidated real estate venture” captions within the Company’s consolidated statements of operations, respectively, from the Austin Portfolio transaction. For further details, see Note 3, "Real Estate Investments."

[2] The decrease in third quarter net income primarily relates to a $56.9 million impairment charge which related to eight office properties in the Company’s Metropolitan Washington, D.C. segment. See Note 3, “Real Estate Investments,” for further information.