Partners Equity of the Operating Partnership - Number of Units and Net Income Used to Calculate Basic and Diluted Earnings Per Common Partnership Unit (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
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic											(369)	(327)	(341)
Preferred Share distributions											0	(2,032)	(6,900)
Preferred share redemption charge											0	(3,181)	0
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted											$ (369)	$ (327)	$ (341)
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 Partnership Unit:
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
BRANDYWINE OPERATING PARTNERSHIP, L.P.
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											(55)	(29)	(15)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic											(369)	(327)	(341)
Preferred Share distributions											0	(2,032)	(6,900)
Preferred share redemption charge											0	(3,181)	0
Net income attributable to common unitholders, Basic											136,865	116,290	33,245
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted											(369)	(327)	(341)
Net income attributable to common unitholders, Diluted											$ 136,865	$ 116,290	$ 33,245
Denominator
Basic weighted average shares outstanding (in shares)											179,959,370	176,964,149	176,523,800
Contingent securities/Share based compensation (in shares)											1,121,744	1,323,816	992,651
Diluted weighted average shares outstanding (in shares)											181,081,114	178,287,965	177,516,451
Earnings per Common Partnership Unit:
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.