Investment In Real Estate Joint Ventures And Partnerships (Narrative) (Details) $ in Thousands		3 Months Ended		12 Months Ended
	Feb. 12, 2016 USD ($) center	Mar. 31, 2016 USD ($) property	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) property center
Schedule of Equity Method Investments [Line Items]
Net basis differentials for equity method investments		$ 2,700		$ 4,900
Impairment loss		1,303	$ 0
Management fees revenues, related parties		$ 1,200	1,200
Number of centers sold	1	3
Proceeds from sale and disposition of property		$ 108,400
Gain on sale of property		45,157	22,522
Assets		4,033,840		$ 3,901,945
Debt, net		1,924,052
Business acquisition, percentage of voting interests acquired	49.00%
Proceeds to acquire businesses, gross	$ 2,500
Gain on sale and acquisition of real estate joint venture and partnership interests		$ 37,392	$ 861
Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures		20.00%		20.00%
Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures		75.00%		75.00%
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Gain on sale of property				$ 1,000
50% Owned Unconsolidated Real Estate Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Gain on sale and acquisition of real estate joint venture and partnership interests				$ 900
50% Owned Unconsolidated Real Estate Joint Venture [Member] | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures				50.00%
Number of centers sold | property		1		1
Proceeds from sale and disposition of property		$ 13,100		$ 1,100
Gain on sale of property		$ 200		$ 600
20% Owned Unconsolidated Real Estate Joint Venture [Member] | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Number of centers sold | property				3
Proceeds from sale and disposition of property				$ 17,600
51% Owned Real Estate joint venture [Member] | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures		66.00%		51.00%
Number o real estate properties acquired | property		1
Gross acquisition purchase price		$ 65,000		$ 54,100
Equity interest in acquiree, percentage				51.00%
Number of real estate properties | center				3
Assets				$ 43,700
Debt, net				$ 72,400