Acquisitions - Summary of Acquisitions (Details) $ in Thousands						6 Months Ended
	May 16, 2017 USD ($) ft² unit	Apr. 05, 2017 USD ($) ft²	Feb. 24, 2017 USD ($) ft²	Jan. 25, 2017 USD ($) a ft²	Jan. 13, 2017 USD ($) ft² VIE	Jun. 30, 2017 USD ($) a ft² phase unit
Main Street Promenade
Business Acquisition [Line Items]
Square footage | ft²					181,600
Purchase price of asset acquisition					$ 88,000
Carillon, formerly known as Boulevard at the Capital Centre
Business Acquisition [Line Items]
Square footage | ft²				0
Purchase price of asset acquisition				$ 2,000
Area of land subject to ground lease | a				70
Area of land in which fee interest was acquired | a				50
Consideration paid for fee interest in land				$ 1,939
Remaining area of land subject to ground lease | a				20		20
Term of ground lease				9 months
Amount of building and improvements derecognized				$ 11,347
Fair value of land received				$ 15,200
Deferred gain						$ 2,524
One Loudoun Downtown - Phase II
Business Acquisition [Line Items]
Square footage | ft²			15,900
Purchase price of asset acquisition			$ 4,128
One Loudoun Downtown - Phase III
Business Acquisition [Line Items]
Square footage | ft²		9,800
Purchase price of asset acquisition		$ 2,193
One Loudoun Downtown - Phase IV
Business Acquisition [Line Items]
Square footage | ft²	0
Purchase price of asset acquisition	$ 3,500
Number of residential units | unit	123					408
One Loudoun Downtown - Phases II through IV
Business Acquisition [Line Items]
Number of phases | phase						3
2017 acquisitions
Business Acquisition [Line Items]
Square footage | ft²						207,300
Purchase price of asset acquisition						$ 99,821
Capitalized closing costs and adjustments						$ 2,334
VIE | Main Street Promenade
Business Acquisition [Line Items]
Number of variable interest entities | VIE					2