Summary of Quarterly Results (Parenthetical) (Details) $ in Thousands			3 Months Ended	12 Months Ended
	Oct. 18, 2017 USD ($) property	Oct. 17, 2017 property	Dec. 31, 2017 USD ($) property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Quarterly Financial Information [Line Items]
Net gain on Real Estate Venture transactions				$ 80,526	$ 20,000	$ 7,229
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Quarterly Financial Information [Line Items]
Net gain on Real Estate Venture transactions				$ 80,526	$ 20,000	$ 7,229
Austin Joint Venture [Member]
Quarterly Financial Information [Line Items]
Net gain on Real Estate Venture transactions	$ 40,092		$ 52,200
Number of Properties Sold \| property	8	7	8
Austin Joint Venture [Member] \| BRANDYWINE OPERATING PARTNERSHIP, L.P.
Quarterly Financial Information [Line Items]
Net gain on Real Estate Venture transactions			$ 52,200
Number of Properties Sold \| property			8