Investment In Real Estate Joint Ventures And Partnerships (Narrative) (Details) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($)	Mar. 31, 2018 USD ($) property	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) property
Schedule of Equity Method Investments [Line Items]
Net basis differentials for equity method investments		$ 3,400		$ 2,200
Joint venture fee income		$ 1,500	$ 1,500
Number of centers sold | property		6
Proceeds from sale and disposition of property		$ 260,700
Gain on sale of property		$ 109,045	$ 15,763
Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures		20.00%
Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures		90.00%
Unconsolidated Real Estate Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures	90.00%
Number of centers sold | property				2
Proceeds from sale and disposition of property		$ 11,700		$ 19,600
Gain on sale of property		$ 2,400		$ 6,200
Gross acquisition purchase price	$ 23,500