Real Estate - Schedule of Construction in Progress (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Real Estate [Line Items]
Construction in progress	$ 317,798	$ 185,972
Glebe Road
Real Estate [Line Items]
Construction in progress	237,305	162,176
7316 Wisconsin Avenue
Real Estate [Line Items]
Construction in progress	42,626	0
Ashbrook Marketplace
Real Estate [Line Items]
Construction in progress	22,570	11,124
Other
Real Estate [Line Items]
Construction in progress	$ 15,297	$ 12,672