Investment in Unconsolidated Real Estate Ventures - Summary of Financial Position of Real Estate Ventures (Details) - USD ($) $ in Thousands		Sep. 30, 2018		Dec. 31, 2017
Schedule Of Equity Method Investments [Line Items]
Net property		$ 920,900		$ 1,083,965
Other assets		146,366		161,932
Other liabilities		91,094		97,707
Debt, net		660,041		766,420
Equity	[1]	316,131		381,770
DRA Austin Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Net property		258,424		263,557
Other assets		39,398		42,272
Other liabilities		18,705		24,131
Debt, net		246,158		248,700
Equity	[1]	32,959		32,998
BDN - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Net property		157,824		158,960
Other assets		23,133		24,181
Other liabilities		4,347		4,493
Debt, net		92,642		92,917
Equity	[1]	83,968		85,731
HSRE-BDN I, LLC (evo at Cira Centre South) [Member]
Schedule Of Equity Method Investments [Line Items]
Net property		0	[2]	143,990
Other assets		0	[2]	8,563
Other liabilities		0	[2]	1,648
Debt, net		0	[2]	110,136
Equity	[1]	0	[2]	40,769
Other Income [Member]
Schedule Of Equity Method Investments [Line Items]
Net property		504,652		517,458
Other assets		83,835		86,916
Other liabilities		68,042		67,435
Debt, net		321,241		314,667
Equity	[1]	$ 199,204		$ 222,272

[1] This amount includes the effect of the basis difference between the Company's historical cost basis and the basis recorded at the Real Estate Venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials occur from the impairment of investments, purchases of third party interests in existing Real Estate Ventures and upon the transfer of assets that were previously owned by the Company into a Real Estate Venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the Real Estate Venture level.

[2] On January 10, 2018, HSRE-BDN I, LLC (evo at Cira Centre South) sold the 345-unit student housing tower, its sole operating asset. See ‘evo at Cira Disposition’ section below