Commitments and Contingencies (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Commitments and Contingencies [Line Items]
Amount of letters of credit outstanding	$ 143
Redevelopment costs incurred	21,300		$ 33,022
Aggregate proceeds, net	187,125	$ 404,996
Reisterstown Road Plaza
Commitments and Contingencies [Line Items]
Redevelopment costs incurred	8,690
Reisterstown Road Plaza | Minimum
Commitments and Contingencies [Line Items]
Net estimated redevelopment costs	9,500
Reisterstown Road Plaza | Maximum
Commitments and Contingencies [Line Items]
Net estimated redevelopment costs	10,500
Redevelopment portion of Circle East, formerly known as Towson Circle
Commitments and Contingencies [Line Items]
Redevelopment costs incurred	7,180
Redevelopment portion of Circle East, formerly known as Towson Circle | Minimum
Commitments and Contingencies [Line Items]
Net estimated redevelopment costs	33,000
Redevelopment portion of Circle East, formerly known as Towson Circle | Maximum
Commitments and Contingencies [Line Items]
Net estimated redevelopment costs	35,000
Redevelopment portion of Circle East, air rights
Commitments and Contingencies [Line Items]
Aggregate proceeds, net	$ 11,820