Partners Equity of the Operating Partnership (Textual) (Details) - USD ($)					1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 06, 2018	Apr. 11, 2017	Jan. 10, 2017	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 03, 2019
Earnings Per Common Partnership Unit [Line Items]
Dividends, Common Stock	$ 33,600,000
Dividends payable, date to be paid	Jan. 22, 2019
Dividends payable, date of record	Jan. 08, 2019
Preferred share redemption charge						$ 0	$ 3,181,000	$ 0
Repurchased and Retired, Shares						1,729,278	0	0
Share Price						$ 12.64
Repurchased and Retired, Value						$ 21,858,000
Common Stock, Par or Stated Value Per Share (USD per share)	$ 0.01					$ 0.01	$ 0.01	$ 0.01
Common Stock, Shares Authorized	400,000,000					400,000,000	400,000,000
Upfront costs							$ 499,000
Common shares issued under offering program								0
Cash proceeds, net of issuance costs						$ 416,000	$ 51,225,000	$ 0
Offering Program [Member]
Earnings Per Common Partnership Unit [Line Items]
Common Stock, Shares Authorized				16,000,000
Upfront costs				$ 200,000
Common shares issued under offering program						23,311	2,858,991	0
Weighted average price per share	$ 18.04					$ 18.04	$ 18.19
Cash proceeds, net of issuance costs						$ 400,000	$ 51,200,000
Common shares remain available for issuance	13,117,698					13,117,698
Subsequent Event [Member]
Earnings Per Common Partnership Unit [Line Items]
Authorized Amount									$ 150,000,000.0
Repurchased and Retired, Shares					1,337,169
Share Price					$ 12.92
Repurchased and Retired, Value					$ 17,300,000
Subsequent Event [Member] | Maximum [Member]
Earnings Per Common Partnership Unit [Line Items]
Authorized Amount									$ 150,000,000
Dividend Declared [Member]
Earnings Per Common Partnership Unit [Line Items]
Dividends Payable, Amount Per Share	$ 0.19					$ 0.19
Class A Units [Member]
Earnings Per Common Partnership Unit [Line Items]
Redeemable Limited Partnership Units Potential Cash Redemption Value Closing Market Price	$ 12.87					$ 12.87	$ 18.19	$ 16.51
Limited Partners' Capital Account, Units Outstanding	982,871					982,871	1,479,799	1,479,799
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Earnings Per Common Partnership Unit [Line Items]
Preferred units outstanding	0					0	0
Dividends, Common Stock		$ 33,600,000
Dividends payable, date to be paid		Jan. 22, 2019
Dividends payable, date of record		Jan. 08, 2019
Preferred share redemption charge						$ 0	$ 3,181,000	$ 0
Repurchase program, number of mirror unit of operating partnership retired for each common share repurchased						1
Cash proceeds, net of issuance costs						$ 416,000	$ 51,225,000	$ 0
BRANDYWINE OPERATING PARTNERSHIP, L.P. | Dividend Declared [Member]
Earnings Per Common Partnership Unit [Line Items]
Dividends Payable, Amount Per Share		$ 0.19
BRANDYWINE OPERATING PARTNERSHIP, L.P. | Series E Preferred Stock [Member]
Earnings Per Common Partnership Unit [Line Items]
Redemption outstanding shares			4,000,000
Redemption price per share			$ 25.51
Accrued dividends paid in cash			$ 2,000,000.0
Preferred share redemption charge			$ 3,200,000