Investments in Unconsolidated Real Estate Joint Ventures (Unconsolidated Real Estate Joint Ventures) (Details) ft² in Thousands, $ in Thousands	1 Months Ended	6 Months Ended
	Jul. 31, 2017 USD ($) Extension	Jun. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) ft²	Dec. 31, 2016 USD ($) ft²
Columbus National Harbor RioCan Canada [Member]
Schedule of Equity Method Investments [Line Items]
Carrying Value of Investment			$ 125,800	$ 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
National Harbor [Member]
Schedule of Equity Method Investments [Line Items]
Ownership %			50.00%	50.00%
Square Feet | ft²			341	341
Carrying Value of Investment			$ 2,400	$ 4,100
RioCan Canda [Member]
Schedule of Equity Method Investments [Line Items]
Ownership %			50.00%	50.00%
Square Feet | ft²			924	901
Carrying Value of Investment			$ 116,600	$ 117,300
Charlotte and Galveston/Houston [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment Reported In Liabilities			$ (16,100)	$ (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			$ (3,600)	$ (2,500)
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			$ (12,500)	$ (3,800)
Unconsolidated Properties [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net			351,322	335,971
Unconsolidated Properties [Member] | Columbus [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net			84,400	84,200
Unconsolidated Properties [Member] | National Harbor [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net			86,400	86,100
Unconsolidated Properties [Member] | RioCan Canda [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net			11,400	11,100
Unconsolidated Properties [Member] | Charlotte [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net			89,800	89,700
Unconsolidated Properties [Member] | Galveston/Houston [Member]
Schedule of Equity Method Investments [Line Items]
Total joint venture debt, net			79,400	64,900
Mortgages [Member] | Unconsolidated Properties [Member]
Schedule of Equity Method Investments [Line Items]
Net discount and debt origination costs			$ (1,600)	$ (1,600)
Mortgages [Member] | Unconsolidated Properties [Member] | Galveston/Houston [Member]
Schedule of Equity Method Investments [Line Items]
Principal	$ 80,000	$ 70,000
Number of mortgage extensions | Extension	2
Term of mortgage extension	1 year
Basis spread on variable rate	1.65%	1.50%
Proceeds from Issuance of Debt	$ 14,500