Acquisitions and Developments in Progress - Summary of Acquisitions (Details) $ in Thousands													3 Months Ended	12 Months Ended
	Aug. 13, 2019 USD ($) ft²	Jun. 10, 2019 USD ($) ft²	Mar. 07, 2019 USD ($) ft²	Dec. 19, 2017 USD ($) ft²	Dec. 11, 2017 USD ($) ft² unit	Aug. 08, 2017 USD ($) ft² phase	Jul. 06, 2017 USD ($) ft²	May 16, 2017 USD ($) ft² unit	Apr. 05, 2017 USD ($) ft²	Feb. 24, 2017 USD ($) ft²	Jan. 25, 2017 USD ($) a ft²	Jan. 13, 2017 USD ($) ft² VIE	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($) a	Dec. 31, 2017 USD ($) ft²
Business Acquisition [Line Items]
Gain on exchange of investment property														$ 0	$ 0	$ 2,524
North Benson Center
Business Acquisition [Line Items]
Square footage | ft²			70,500
Purchase price of asset acquisition			$ 25,340
Paradise Valley Marketplace - Parcel
Business Acquisition [Line Items]
Square footage | ft²		0
Purchase price of asset acquisition		$ 1,343
Southlake Town Square - Parcel
Business Acquisition [Line Items]
Square footage | ft²	3,100
Purchase price of asset acquisition	$ 3,293
2019 acquisitions
Business Acquisition [Line Items]
Square footage | ft²														73,600
Purchase price of asset acquisition														$ 29,976
Capitalized closing costs and adjustments														$ 316
One Loudoun Uptown
Business Acquisition [Line Items]
Purchase price of asset acquisition															25,000
Capitalized closing costs and adjustments															$ 450
Acres of land | a															58
Acres of land that are developable | a															32
Main Street Promenade
Business Acquisition [Line Items]
Square footage | ft²												181,600
Purchase price of asset acquisition												$ 88,000
Carillon - Fee Interest
Business Acquisition [Line Items]
Square footage | ft²											0
Purchase price of asset acquisition											$ 2,000
Land subject to ground lease | a											70
Fee interest in land acquired | a											50
Consideration paid for fee interest in land											$ 1,939
Remaining land subject to ground lease | a											20
Term of ground lease											9 months
Amount of building and improvements derecognized											$ 11,347
Fair value of land received											$ 15,200
Gain on exchange of investment property													$ 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
New Hyde Park Shopping Center
Business Acquisition [Line Items]
Square footage | ft²							32,300
Purchase price of asset acquisition							$ 22,075
One Loudoun Downtown - Phase V
Business Acquisition [Line Items]
Square footage | ft²						17,700
Purchase price of asset acquisition						$ 5,167
One Loudoun Downtown - Phase VI
Business Acquisition [Line Items]
Square footage | ft²						74,100
Purchase price of asset acquisition						$ 20,523
Plaza del Lago
Business Acquisition [Line Items]
Square footage | ft²					109,000
Purchase price of asset acquisition					$ 48,300
Number of residential units | unit					15
Southlake Town Square - Outparcel
Business Acquisition [Line Items]
Square footage | ft²				12,200
Purchase price of asset acquisition				$ 7,029
2017 acquisitions
Business Acquisition [Line Items]
Square footage | ft²													443,800			443,800
Purchase price of asset acquisition																$ 202,915
Capitalized closing costs and adjustments																$ 2,506
One Loudoun Downtown - Phases II through VI
Business Acquisition [Line Items]
Number of phases | phase						5
One Loudoun Downtown
Business Acquisition [Line Items]
Number of residential units | unit								408
Retail | Plaza del Lago
Business Acquisition [Line Items]
Square footage | ft²					100,200
Residential | Plaza del Lago
Business Acquisition [Line Items]
Square footage | ft²					8,800
VIE | Main Street Promenade
Business Acquisition [Line Items]
Number of variable interest entities | VIE												2