Discontinued Operations - Schedule of Assets and Liabilities and Results of Operations Related to Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Balance Sheets:
Assets related to discontinued operations	$ 103,787		$ 103,787		$ 104,836
Other Income:
Income from discontinued operations, net	2,147	$ 3,040	5,815	$ 7,202
1899 Pennsylvania Avenue [Member]
Revenues:
Rental revenue	3,556		10,634
Fee and other income	85		215
Total revenues	3,641		10,849
Expenses:
Operating	1,483		4,333
Depreciation and amortization			690
Total expenses	1,483		5,023
Other Income:
Income before income taxes	2,158		5,826
Income tax expense	(11)		(11)
Income from discontinued operations, net	2,147		5,815
1899 Pennsylvania Avenue [Member] | Discontinued Operations Held for Sale [Member]
Balance Sheets:
Real estate, net	93,837		93,837		94,251
Deferred rent receivable	3,880		3,880		4,206
Deferred charges, net	780		780		804
Intangible assets, net	5,290		5,290		5,575
Assets related to discontinued operations	$ 103,787		$ 103,787		$ 104,836
1899 Pennsylvania Avenue and Liberty Place [Member]
Revenues:
Rental revenue		6,964		21,335
Fee and other income		100		372
Total revenues		7,064		21,707
Expenses:
Operating		2,802		8,558
Depreciation and amortization		2,362		7,087
Total expenses		5,164		15,645
Other Income:
Gain on sale of real estate		1,140		1,140
Income before income taxes		3,040		7,202
Income from discontinued operations, net		$ 3,040		$ 7,202