Dispositions and Discontinued Operations - Schedule of Cash Flows from Discontinued Operations (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
1899 Pennsylvania Avenue [Member]
Statements of Cash Flows:
Cash provided by operating activities		$ 5,522	$ 15,949
Cash provided by investing activities		89,206	148,793
Proceeds from sale of real estate	[1]	89,206	150,307
Additions to real estate			(1,514)
Total cash provided by investing activities		89,206	148,793
Cash used in financing activities		(96,896)	(162,294)
Additional Cash Flow Information:
Depreciation and amortization		$ 690	$ 8,243
1899 Pennsylvania Avenue, Liberty Place, 425 Eye Street and 2099 Pennsylvania Avenue [Member]
Statements of Cash Flows:
Cash provided by operating activities				$ 25,416
Cash provided by investing activities				345,010
Proceeds from sale of real estate	[1]			349,013
Additions to real estate				(4,003)
Total cash provided by investing activities				345,010
Cash used in financing activities				(370,626)
Additional Cash Flow Information:
Depreciation and amortization				$ 17,357

[1] Represents the proceeds from the sale of 1899 Pennsylvania Avenue in 2020, Liberty Place in 2019, and 425 Eye Street and 2099 Pennsylvania Avenue in 2018.