Real Estate Investments - Summary of Properties Sold (Details) $ in Thousands		3 Months Ended
	Mar. 19, 2020 USD ($) ft²	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from the sale of properties		$ 17,711	$ 5,273
Gain (loss) on sale		$ 2,586	$ 0
Office properties | 52 East Swedesford Road
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable area (in square feet) | ft²	131,077
Proceeds from the sale of properties	$ 18,000
Gain (loss) on sale	$ 2,336