Segment Information - Real Estate Investments, at Cost of Company's Reportable Segments (Additional Information) (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2020 a property	Dec. 31, 2019 a
3001-3003 and 3025 JFK Boulevard
Segment Reporting Information [Line Items]
Lease agreement term	99 years	99 years
Held-for-sale | Land Held For Development
Segment Reporting Information [Line Items]
Area of land (in acres)	35.2
Other | Held-for-sale | Land Held For Development
Segment Reporting Information [Line Items]
Area of land (in acres)		35.2
Philadelphia CBD
Segment Reporting Information [Line Items]
Number of properties held for sale | property	2