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, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator
Net income (loss)	$ 73,844	[1]	$ 19,046	$ 7,698	$ 21,271	$ (12,370)	$ 7,884	$ (1,323)	$ 46,310	$ 121,859	$ 40,501	$ (30,740)
Net (income) loss attributable to noncontrolling interests, Basic										(1,009)	(310)	339
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic										(327)	(341)	(329)
Distribution to preferred shareholders										(2,032)	(6,900)	(6,900)
Preferred share redemption charge										(3,181)	0	0
Net income (loss) attributable to Common Shareholders of Brandywine Realty Trust										115,310	32,950	(37,630)
Net (income) loss attributable to noncontrolling interests, Diluted										(1,009)	(310)	339
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted										(327)	(341)	(329)
Net income (loss) attributable to common shareholders, Diluted										$ 115,310	$ 32,950	$ (37,630)
Denominator
Basic weighted average shares outstanding (in shares)										175,484,350	175,018,163	178,162,160
Contingent securities/Share based compensation (in shares)										1,323,816	992,651	0
Diluted weighted average shares outstanding (in shares)										176,808,166	176,010,814	178,162,160
Earnings (loss) per Common Share:
Net income (loss) attributable to common shareholders, Basic (USD per share)	$ 0.42		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.66	$ 0.19	$ (0.21)
Net income (loss) attributable to common shareholders, Diluted (USD per share)	$ 0.41		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.65	$ 0.19	$ (0.21)

[1] The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures."