PARTNER'S EQUITY OF THE PARENT COMPANY - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Dec. 08, 2020	Jan. 10, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 03, 2019
Earnings Per Common Partnership Unit [Line Items]
Dividends, common stock	$ 32,700
Repurchased and retired (in shares)			6,248,483	1,337,169	1,729,278	0
Share price (in usd per share)			$ 9.60	$ 12.92	$ 12.64
Repurchased and retired, value			$ 59,999	$ 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
Cash proceeds, net of issuance costs			$ 0	$ 0	$ 416
Common shares remain available for issuance (in shares)			0
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	0	23,311
Weighted average price per share (usd per share)					$ 18.04
Cash proceeds, net of issuance costs					$ 400
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)			$ 11.91	$ 15.75	$ 12.87
Limited partners' capital account, units outstanding (in units)			981,634	981,634	982,871
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Earnings Per Common Partnership Unit [Line Items]
Preferred units, outstanding (in units)			0	0
Repurchase program, number of mirror unit of operating partnership retired for each common share repurchased			1
Cash proceeds, net of issuance costs			$ 0	$ 0	$ 416