Investment in Unconsolidated Real Estate Ventures - Summary of Results of Operations of Real Estate Ventures with Interests (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) ft² property	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) ft² property	Sep. 30, 2018 USD ($)	Dec. 11, 2018 ft² property	Mar. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity in income (loss) of Real Estate Ventures	$ (1,965)	$ 1	$ (4,814)	$ (1,182)
Number of properties | property	95		95
Net rentable area (in square feet) | ft²	16,711,387		16,711,387
DRA (G&I) Austin
Schedule of Equity Method Investments [Line Items]
Revenue	$ 0	14,232	$ 0	42,492
Operating expenses	0	(6,428)	0	(18,245)
Interest expense, net	0	(2,549)	0	(7,070)
Depreciation and amortization	0	(4,896)	0	(15,622)
(Gain) loss on early extinguishment of debt	0	0	0	0
Net income (loss)	$ 0	$ 359	$ 0	$ 1,555
Ownership interest %	0.00%	50.00%	0.00%	50.00%	50.00%
Company's share of net income (loss)	$ 0	$ 180	$ 0	$ 778
Basis adjustments and other	0	243	0	378
Equity in income (loss) of Real Estate Ventures	0	423	0	1,156
Number of properties | property					12
Net rentable area (in square feet) | ft²					1,570,123
Brandywine-AI Ventures LLC
Schedule of Equity Method Investments [Line Items]
Revenue	1,360	5,962	5,050	17,768
Operating expenses	(871)	(2,589)	(2,473)	(8,010)
Interest expense, net	(222)	(873)	(698)	(2,606)
Depreciation and amortization	(540)	(2,232)	(2,055)	(6,915)
(Gain) loss on early extinguishment of debt	4,371	0	4,371	0
Net income (loss)	$ 4,098	$ 268	$ 4,195	$ 237
Ownership interest %	50.00%	50.00%	50.00%	50.00%
Company's share of net income (loss)	$ 2,049	$ 134	$ 2,098	$ 119
Basis adjustments and other	31	31	101	33
Equity in income (loss) of Real Estate Ventures	$ 2,080	$ 165	2,199	152
Evo At Cira Centre South Venture
Schedule of Equity Method Investments [Line Items]
Revenue			0	995
Operating expenses			0	(250)
Interest expense, net			0	(388)
Depreciation and amortization			0	(376)
(Gain) loss on early extinguishment of debt			0	(718)
Net income (loss)			$ 0	$ (737)
Ownership interest %	0.00%	50.00%	0.00%	50.00%		50.00%
Company's share of net income (loss)			$ 0	$ (369)
Basis adjustments and other			0	11
Equity in income (loss) of Real Estate Ventures			0	(358)
MAP Venture
Schedule of Equity Method Investments [Line Items]
Revenue	$ 17,476	$ 17,243	53,560	50,976
Operating expenses	(11,981)	(10,219)	(35,747)	(30,347)
Interest expense, net	(2,436)	(2,894)	(7,504)	(10,426)
Depreciation and amortization	(6,247)	(4,654)	(19,146)	(14,096)
(Gain) loss on early extinguishment of debt	0	(334)	0	(334)
Net income (loss)	$ (3,188)	$ (858)	$ (8,837)	$ (4,227)
Ownership interest %	50.00%	50.00%	50.00%	50.00%
Company's share of net income (loss)	$ (1,594)	$ (429)	$ (4,419)	$ (2,114)
Basis adjustments and other	(28)	(15)	(69)	(39)
Equity in income (loss) of Real Estate Ventures	(1,622)	(444)	(4,488)	(2,153)
Other
Schedule of Equity Method Investments [Line Items]
Revenue	13,890	4,580	42,538	13,708
Operating expenses	(5,017)	(1,904)	(15,736)	(5,145)
Interest expense, net	(3,522)	(1,228)	(8,219)	(3,132)
Depreciation and amortization	(6,307)	(1,481)	(19,078)	(4,430)
(Gain) loss on early extinguishment of debt	0	0	0	0
Net income (loss)	(956)	(33)	(495)	1,001
Company's share of net income (loss)	(2,400)	(121)	(2,444)	168
Basis adjustments and other	(23)	(22)	(81)	(147)
Equity in income (loss) of Real Estate Ventures	(2,423)	144	(2,525)	21
Unconsolidated Real Estate Ventures
Schedule of Equity Method Investments [Line Items]
Revenue	32,726	42,017	101,148	125,939
Operating expenses	(17,869)	(21,140)	(53,956)	(61,997)
Interest expense, net	(6,180)	(7,544)	(16,421)	(23,622)
Depreciation and amortization	(13,094)	(13,263)	(40,279)	(41,439)
(Gain) loss on early extinguishment of debt	4,371	(334)	4,371	(1,052)
Net income (loss)	(46)	(264)	(5,137)	(2,171)
Company's share of net income (loss)	(1,945)	(236)	(4,765)	(1,418)
Basis adjustments and other	(20)	237	(49)	236
Equity in income (loss) of Real Estate Ventures	$ (1,965)	$ 1	$ (4,814)	$ (1,182)
Minimum
Schedule of Equity Method Investments [Line Items]
Ownership interest %	15.00%		15.00%
Minimum | Unconsolidated Real Estate Ventures
Schedule of Equity Method Investments [Line Items]
Ownership interest %	15.00%	25.00%	15.00%	25.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Ownership interest %	70.00%		70.00%
Maximum | Unconsolidated Real Estate Ventures
Schedule of Equity Method Investments [Line Items]
Ownership interest %	70.00%	70.00%	70.00%	70.00%