Investment In Real Estate Joint Ventures And Partnerships (Narrative) (Details) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
	Feb. 12, 2016 USD ($) center	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) property	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) property center
Schedule of Equity Method Investments [Line Items]
Net basis differentials for equity method investments		$ 2,600		$ 2,600		$ 4,900
Impairment loss		0	$ 7,487	1,303	$ 7,487
Management fees revenues, related parties		1,100	1,100	$ 2,300	2,300
Number of centers sold	1			3
Proceeds from sale and disposition of property				$ 110,400
Gain on sale of property				46,190	30,685	1,000
Gross acquisition purchase price				93,200
Assets		4,032,927		4,032,927		$ 3,901,945
Debt, net		1,871,510		1,871,510
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		$ 0	$ 18	$ 37,392	$ 879
Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures		20.00%		20.00%		20.00%
Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures		75.00%		75.00%		75.00%
50% Owned Unconsolidated Real Estate Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures						50.00%
Number of centers sold | property				4		1
Proceeds from sale and disposition of property				$ 63,700		$ 1,100
Gain on sale of property				$ 3,400		600
Gain on sale and acquisition of real estate joint venture and partnership interests						$ 900
20% Owned Unconsolidated Real Estate Joint Venture [Member]
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]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in joint ventures		66.00%		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