PARTNER'S EQUITY OF THE PARENT COMPANY - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Dec. 11, 2019	Apr. 11, 2017	Jan. 10, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 03, 2019
Earnings Per Common Partnership Unit [Line Items]
Dividends, common stock	$ 33,800
Preferred share redemption charge				$ 0	$ 0	$ 3,181
Repurchased and retired (in shares)				1,337,169	1,729,278	0
Share price (in usd per share)				$ 12.92	$ 12.64
Repurchased and retired, value				$ 17,281	$ 21,858
Common stock, par or stated value per share (usd per share)				$ 0.01	$ 0.01
Common Stock, Shares Authorized (in shares)				400,000,000	400,000,000
Upfront costs						$ 499
Cash proceeds, net of issuance costs				$ 0	$ 416	$ 51,225
Offering Program
Earnings Per Common Partnership Unit [Line Items]
Common Stock, Shares Authorized (in shares)			16,000,000
Upfront costs			$ 200
Common shares issued under offering program (in shares)				0	23,311	2,858,991
Weighted average price per share (usd per share)					$ 18.04	$ 18.19
Cash proceeds, net of issuance costs					$ 400	$ 51,200
Common shares remain available for issuance (in shares)				13,117,698
Maximum
Earnings Per Common Partnership Unit [Line Items]
Authorized amount							$ 150,000
Dividend Declared
Earnings Per Common Partnership Unit [Line Items]
Dividends payable, amount per share (in usd per share)	$ 0.19
Class A Units
Earnings Per Common Partnership Unit [Line Items]
Redeemable limited partnership unit price (in usd per unit)				$ 15.75	$ 12.87	$ 18.19
Limited partners' capital account, units outstanding (in units)				981,634	982,871	1,479,799
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Earnings Per Common Partnership Unit [Line Items]
Preferred units, outstanding (in units)				0	0
Dividends, common stock	$ 33,800
Preferred share redemption charge				$ 0	$ 0	$ 3,181
Repurchase program, number of mirror unit of operating partnership retired for each common share repurchased				1
Cash proceeds, net of issuance costs				$ 0	$ 416	$ 51,225
BRANDYWINE OPERATING PARTNERSHIP, L.P. | Dividend Declared
Earnings Per Common Partnership Unit [Line Items]
Dividends payable, amount per share (in usd per share)	$ 0.19
BRANDYWINE OPERATING PARTNERSHIP, L.P. | Series E Preferred Stock
Earnings Per Common Partnership Unit [Line Items]
Redemption outstanding shares (in shares)		4,000,000
Redemption price per share (in usd per share)		$ 25.51
Accrued dividends paid in cash		$ 2,000
Preferred share redemption charge		$ 3,200