Segment Information Summary of Unconsolidated Real Estate Ventures (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Investment in Real Estate Ventures, at equity		$ 201,034		$ 201,034		$ 225,004
Equity in loss of Real Estate Ventures		(873)	$ (489)	(742)	$ (247)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Investment in Real Estate Ventures, at equity		201,034		201,034		225,004
Equity in loss of Real Estate Ventures		(873)	(489)	(742)	(247)
Operating Segments [Member] | Philadelphia CBD [Member]
Segment Reporting Information [Line Items]
Investment in Real Estate Ventures, at equity	[1]	33,961		33,961		27,137
Equity in loss of Real Estate Ventures	[1]	(150)	0	(450)	(21)
Operating Segments [Member] | Pennsylvania [Member]
Segment Reporting Information [Line Items]
Investment in Real Estate Ventures, at equity		17,220		17,220		17,385
Equity in loss of Real Estate Ventures		(17)	(391)	(22)	(359)
Operating Segments [Member] | Metropolitan Dc [Member]
Segment Reporting Information [Line Items]
Investment in Real Estate Ventures, at equity		109,249		109,249		73,127
Equity in loss of Real Estate Ventures		(179)	(42)	(229)	25
Operating Segments [Member] | New Jersey/ Delaware [Member]
Segment Reporting Information [Line Items]
Investment in Real Estate Ventures, at equity		0		0		0
Equity in loss of Real Estate Ventures		116	103	164	122
Operating Segments [Member] | Richmond, Virginia [Member]
Segment Reporting Information [Line Items]
Investment in Real Estate Ventures, at equity		1,506		1,506		1,574
Equity in loss of Real Estate Ventures		246	115	331	69
Operating Segments [Member] | Austin, Texas [Member]
Segment Reporting Information [Line Items]
Investment in Real Estate Ventures, at equity	[2],[3]	39,098		39,098		$ 105,781
Equity in loss of Real Estate Ventures	[2],[3]	$ (889)	$ (274)	$ (536)	$ (83)

[1] Equity in income as of June 30, 2014 did not include evo at Cira, which was placed into service during the third quarter ended September 30, 2014.

[2] Investment in real estate ventures does not include the $1.2 million negative investment balance in one real estate venture as of June 30, 2015 and December 31, 2014, which is included in other liabilities.

[3] On June 22, 2015 the Company acquired the remaining 50.0% of the common interest in Broadmoor Austin Associates. As such, equity method investment at June 30, 2015 related to the Austin Venture only. See Note 3, "Real Estate Investments," for further information regarding the purchase of Broadmoor Austin Associates.