Real Estate - Variable Interest Entities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016		Dec. 31, 2015
Real Estate Properties [Line Items]
Land	$ 561,256		$ 561,256
Accounts payable and other liabilities	56,348		45,367
Tenant security deposits	$ 9,604		9,378
Six Fifty North Glebe Road [Member]
Real Estate Properties [Line Items]
Variable interest entity, qualitative or quantitative information, ownership percentage	90.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	10.00%
Land	$ 12,851		12,851
Investment Building and Building Improvements	37,937		37,791
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(2,902)		(2,347)
Other Assets	828		1,188
Real Estate Investments, Joint Ventures	48,714		49,483
Loans Payable	32,215	[1]	32,214
Accounts payable and other liabilities	324		256
Tenant security deposits	83		82
Accounts payable and accrued liabilities related to joint ventures	$ 32,622		$ 32,552

[1] The mortgage notes payable balance as of March 31, 2016 is eliminated in consolidation due to the purchase of the loan by Washington REIT in January 2016.