Real Estate Investments - Purchase Price Allocation (Details) - Four Tower Bridge [Member] $ in Thousands	Jan. 05, 2018 USD ($)
Business Acquisition [Line Items]
Building, land and improvements	$ 20,734
Intangible assets acquired	3,144	[1]
Below market lease liabilities assumed	(182)	[2]
Total unencumbered acquisition value	23,696
Mortgage debt assumed - at fair value	(9,940)	[3]
Total encumbered acquisition value	13,756
Total unencumbered acquisition value	23,696
Mortgage debt assumed - at fair value	(9,940)	[3]
Investment in unconsolidated real estate ventures	(3,502)
Net working capital assumed	1,379
Gain on real estate venture transactions	$ 11,633

[1] Weighted average amortization period of 4.1 years.

[2] Weighted average amortization period of 4.8 years.

[3] The outstanding principal balance on mortgage debt assumed at January 5, 2018 was $9.7 million.