Summary of Quarterly Results (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
Quarterly Financial Information [Line Items]
Total revenue	$ 139,203	[1]	$ 134,998		$ 133,786	$ 136,358	$ 133,344	$ 128,438	$ 127,791	$ 130,920	$ 544,345	$ 520,493	$ 525,463
Net income (loss)	122,710	[2]	(43,262)	[3]	13,136	44,705	73,844	19,046	7,698	21,271	137,289	121,859	40,501
Net income (loss) allocated to Common Shares/ Partnership Unitholders	$ 121,823		$ (43,003)		$ 12,920	$ 44,215	$ 73,137	$ 18,803	$ 4,092	$ 19,278	$ 136,324	$ 120,850	$ 40,191
Basic earnings (loss) per Common Shares/Partnership Unitholders	$ 0.68		$ (0.24)		$ 0.07	$ 0.25	$ 0.42	$ 0.11	$ 0.02	$ 0.11	$ 0.76	$ 0.66	$ 0.19
Diluted earnings (loss) per Common Share/ Partnership Unitholders	$ 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.
Quarterly Financial Information [Line Items]
Total revenue	$ 139,203	[1]	$ 134,998		$ 133,786	$ 136,358	$ 133,344	$ 128,438	$ 127,791	$ 130,920	$ 544,345	$ 520,493	$ 525,463
Net income (loss)	122,710	[2]	(43,262)	[3]	13,136	44,705	73,844	19,046	7,698	21,271	$ 137,289	$ 121,859	$ 40,501
Net income (loss) allocated to Common Shares/ Partnership Unitholders	$ 122,612		$ (43,362)		$ 13,029	$ 44,586	$ 73,758	$ 18,961	$ 4,129	$ 19,442
Basic earnings (loss) per Common Shares/Partnership Unitholders	$ 0.68		$ (0.24)		$ 0.07	$ 0.25	$ 0.42	$ 0.11	$ 0.02	$ 0.11	$ 0.76	$ 0.66	$ 0.19
Diluted earnings (loss) per Common Share/ Partnership Unitholders	$ 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 fourth quarter revenues primarily relates to the acquisition of the Austin Portfolio, located in Austin, Texas, on December 11, 2018. See Note 3, “Real Estate Investments,” for further information on this transaction.

[2] 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."

[3] 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.