Investments in Unconsolidated Real Estate Joint Ventures (Unconsolidated Real Estate Joint Ventures) (Details) ft² in Thousands, $ in Thousands	Jun. 30, 2017 USD ($) ft²	Dec. 31, 2016 USD ($) ft²
Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net	$ 336,387	$ 335,971
Columbus National Harbor RioCan Canada [Member]
Schedule of Equity Method Investments [Line Items]
Carrying Value of Investment	$ 131,200	$ 128,100
Columbus [Member]
Schedule of Equity Method Investments [Line Items]
Ownership %	50.00%	50.00%
Square Feet | ft²	355	355
Carrying Value of Investment	$ 6,800	$ 6,700
Columbus [Member] | Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net	$ 84,300	$ 84,200
National Harbor [Member]
Schedule of Equity Method Investments [Line Items]
Ownership %	50.00%	50.00%
Square Feet | ft²	341	341
Carrying Value of Investment	$ 2,800	$ 4,100
National Harbor [Member] | Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net	$ 86,300	$ 86,100
RioCan Canda [Member]
Schedule of Equity Method Investments [Line Items]
Ownership %	50.00%	50.00%
Square Feet | ft²	924	901
Carrying Value of Investment	$ 121,600	$ 117,300
RioCan Canda [Member] | Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net	11,100	11,100
Charlotte and Galveston/Houston [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment Reported In Liabilities	$ (8,000)	$ (6,300)
Charlotte [Member]
Schedule of Equity Method Investments [Line Items]
Ownership %	50.00%	50.00%
Square Feet | ft²	398	398
Equity Method Investment Reported In Liabilities	$ (3,100)	$ (2,500)
Charlotte [Member] | Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net	$ 89,800	$ 89,700
Galveston/Houston [Member]
Schedule of Equity Method Investments [Line Items]
Ownership %	50.00%	50.00%
Square Feet | ft²	353	353
Equity Method Investment Reported In Liabilities	$ (4,900)	$ (3,800)
Galveston/Houston [Member] | Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net	$ 64,900	$ 64,900