Segment Information - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Parenthetical) (Details) - USD ($) $ in Thousands		9 Months Ended
	Aug. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Deconsolidated mortgage loan		$ 20,582	$ 0
Deconsolidated financing liability		12,384	$ 0
Other liabilities		31,399		$ 31,379
evo at Cira Centre South Venture [Member]
Segment Reporting Information [Line Items]
Net increase of investment in unconsolidated real estate ventures		$ 4,800
Brandywine - AI Venture LLC [Member] | 3141 Fairview Park Drive [Member]
Segment Reporting Information [Line Items]
Deconsolidated net assets	$ 45,600
Deconsolidated mortgage loan	20,582
Deconsolidated financing liability	$ 12,384
Coppell Associates [Member]
Segment Reporting Information [Line Items]
Other liabilities				$ 1,100